Talk:Work (thermodynamics)

sec pressure-volume work

1. If work is an inexact differential as it is acknowledge and, it is actually, the greek letter delta should be use throught the article incluiding the section pressure-volume work.

2. The following wording is not accurate: "Like all work functions, PV work is path-dependent..." The word 'all' may confuse the reader. It is true at all quantitative expressions of work are path dependent if no further remarks are revealed. But, consider that all form of adiabatic work are path indepent, being this an statemente of the First Law. And please consider that by stating 'adiabatic work' you are not determining the path along the process occurs but a restrection: there may be actually many adiabatic paths conecting two given thermodynamic states all leading to the same amount of work. Thus, adiabatic work, no matter it is quantitative expression, is path independent and it can be regarded as 'work function'.

In the same way, consider that adiabatic PV work is a 'state function'. So the phase "From a thermodynamic perspective, this fact implies that PV work is not a state function." should be carefully rewritten.

3. Perphaps a subscript e should be added to external pressure. This is customary in thermodynamics literature so as to distiguish pressure ---as an equilibrium property of the thermodynamical system--- (p) from external pressure (p_e).

4. 'W= Work done on the system' may lead the reader to consider that work done by the system is different.

Etaoin Shdrlu 11:56, 7 October 2006 (UTC)

I'm not much of an expert in this field, but doesn't anyone think it's rather inconsistent to use dE = dQ - dW, where dW is defined as the work done by the system, and then use dW=-PdV, where dW is instead defined as the work done on a system? If it's convention, at least note this to the reader. 208.120.192.196 00:51, 15 April 2007 (UTC)

I do think it is a problem to use the physics sign convention in dE = dQ - dW, and then to define dw as -PdV rather than as +PdV. It seems to be wrong.Lawrence Chemistry (talk) 13:44, 6 January 2009 (UTC)

I expanded on the path dependancy; I hope it makes sense. I thought that a slightly more physical explanation should precede the mathematical explanation, since many readers may be students less familiar with the math (just a guess). I don't think I addressed the above issues, however. I lack a good reference to use for a citation; hopefully someone else can read it, adjust/correct if needed, and provide a good reference, as I think this discussion is important to really understand the topic. Dhollm (talk) 08:25, 24 August 2010 (UTC)

How different

How is thermodynamic work different from mechanical work? Joules is joules, right? Gerardw (talk) 12:00, 17 March 2010 (UTC)

Mechanical work can be a well defined concept when thermodynamics does not apply. Take e.g. the free expansion experiment. Here we have a gas in a closed volume. The enclosure is insulated. The gas is constrained to be in part of the volume and then released into the whole of the enclosure. Then since the entire enclosure is insulated and at a constant volume, the total internal energy stays the same.

We can describe this process using thermodynamics only when comparing the initial equilibrium state to the final equilibrium state. What we cannot do is describe what happens during the process when the gas violently shoots out of the small volume to fill the whole enclosure. However, you can apply the concept of mechanical work to argue that since the gas is expanding in a vacuum and the vacuum cannot exert a force on the gas, that therefore the gas does no work. But this statement cannot formulated in terms of thermodynamic work as the pressure of the gas is not defined during free expansion. It is not ok. to say that dW = -p dV = 0 because p is supposed to be 0.

To see in more detail why it is wrong to take the thermodynamic pressure of the gas to be zero, consider doing the free expansion experiment in infintessimal steps. In the enclosure that is filled up to volume V_0 and th rest is vacuum. We add an extra boundary at V_0 + delta V_0. The space between V_0 and V_0 + delta V_0 is vacuum. We then release the gas so that it fills the volume V_0 + delta V_0. We choose Delta V_0 extremely small, much smaller than the collision length between the molecules. CLearly, in this case P is almost well defined during the expansion and can be taken to be the intitial pressure with negligible error.

Now, what is the meaning of p dV here? The answer is as follows. We are doing an infinitessimal expansion. Before and after the expansion the gas can always be described by thermodynamics. But because in this case the change is infintessimal, the equation

dE = T dS - P dV

holds. This is not because P dV is work and T dS is heat, but simply because E is a state variable that can be specified by S and V. We have a function E(S, V) and the partial derivatives S and V are T and -P (because in the special case where the changes happen in a reversible we know what they are). In this case the change is irreversible and P dV is definitely not work and T dS not the heat supplied. Instead what we do know is that dE = 0, therefore we must have that

T dS = P dV

So, we see that the entropy of the system increases, despite the fact that no heat is supplied to the gas. Spo, the equation dS = dQ/T doesn't hold here. Note that dS = dQ/T holds when supplying heat in quasistatic way in which internal equilibrium is always maintained. In this case the gas in not in thermal equilibrium during the infintessimal expansion.

We can, however, still think of the P dV term as work that we could have extracted from the system, had the gas bumped into a movable piston. However, since the "piston" in this case is locked this energy gets dissppated in the gas itself and this is then effectively the same as adding the same amount of energy to the system as heat. So, that's why we get dS = P dV/T.

From the mechanical POV, you could say that since we don't extract work from the system, we should have p = 0 in some sense, that p not being the same as the thermodynamoc pressure. But then p is the force exerted on the gas and V is taken to be te volume of the extended volume V_0 + delta V_0. Then the pressure is zero, until the gas bumps into the boundary of V_0 + delta V_0, but the volume doesn't change so no work is done. Count Iblis (talk) 15:17, 17 March 2010 (UTC)

From my simple perspective on these things I can offer Gerardw a different kind of answer. Work is related to energy. (They can both be expressed in the same units eg Joules.) Explaining and defining energy in general terms can be a challenging task, and the result is likely to be unsatisfying to a newcomer, particularly a young student. But dividing energy into different manifestations, such as kinetic energy and chemical energy and thermal energy, makes the task of explaining and defining so much easier. Similarly, explaining and defining work in general terms can be a challenging task and the result is likely to be unsatisfying. But separately explaining and defining different manifestations of work, such as mechanical work, thermodynamic work and electrical work, is so much easier and more satisfying. Dolphin51 (talk) 22:39, 17 March 2010 (UTC)

SI Units

The article tells us the non-SI units of Work (thermodynamics), in L(atm) but never tells us the one in SI units. —Preceding unsigned comment added by 75.60.231.85 (talk) 07:14, 22 November 2010 (UTC)

Fixed. Better late than never. Dirac66 (talk) 21:08, 14 April 2013 (UTC)

Requested move

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: page moved to Work (thermodynamics). Consensus was to move, the target was less sure. This was the name that the article was at before the recent move that caused this discussion. If I got the target wrong, let me know. Vegaswikian (talk) 00:42, 26 January 2012 (UTC)

---

Thermodynamical work → Thermodynamic work – Both wikt:thermodynamic and wikt:thermodynamical are adjectives, but Thermodynamic is more commonly used. thermodynamic work gets 49,000 google hits, thermodynamical 1700. Request move per WP:COMMONNAME Nobody Ent 17:58, 19 January 2012 (UTC)

If you're going to rename it, it should be called Work (thermodynamics) (which now redirects to it), in order to correspond with Work (physics), and so on, and then you can say it's also called thermodynamic work or (less commonly) thermodynamical work in the lede. And by the way, I see that some busybody has moved work (physics) to mechanical work without any discussion, and now wants to change THIS article to correspond. Wrong! The key thing about all this stuff is that it's kinds of work. It really should be work (electrical) not electrical work. So now it's all screwed up. Next you're going to want Planet Mercury instead of Mercury (planet). Come on. SBHarris 19:32, 19 January 2012 (UTC)

I'd support moving the article back to Work (thermodynamics) for the reasons Sbharris gives above. Nobody Ent 19:40, 19 January 2012 (UTC)

In order to be consequent, I think "thermodynamical" is better:

• Mechanical work
• Electrical work
• Thermodynamical work

Or without the "-al":

• Mechanic work
• Electric work
• Thermodynamic work

But note, "mechanical work" is more common than "mechanic work". Another option:

• Work (mechanics)
• Work (electrics)
• Work (thermodynamics)

Mixing these would be unreasonable. And "Work (physics)" can refer to any of these, therefore can't replace "Work (mechanics)" Kontos (talk) 19:43, 19 January 2012 (UTC)

We are consistent with the terms actually used in English. Unfortunately English itself is inconsistent. "Mechanic work" would most commonly be understood as work done by a person (e.g. auto repair). Nobody Ent 19:48, 19 January 2012 (UTC)

I see. Then, I think, the "Work (mechanics) - Work (electrics) - Work (thermodynamics)" pattern would be the most proper option. And, I think, it would be good if a separate article discussed the term "Work" in general under the title Work (physics). Kontos (talk) —Preceding undated comment added 19:56, 19 January 2012 (UTC).

Yes. One real problem is that "mechanical work" (like matter) is not well-defined in the sciences, as you note from the article about it here (which would subsume electrical work as written). Like matter, mechanical work might have its own article but only to say that it's a non-universally defined term used most often not for any work done by any force (which is work (physics), but rather work using contact forces between ordinary objects, such as frictional work, or work done by the force of contact pushes and pulls. Work in general as force*distance is (again) work (physics) and it encompases all work done by all of the four basic forces over distance.

Of course it encompasses electrical work (a subset of it). Charges feel EM forces, and that's usually how you do work on charges or objects containg charges (with a few exceptions using the other 3 forces of nature). By contrast, it's impossible to do work through a force of physical contact except through electrical forces, since that's what "contact" is. The reason your hand doesn't go through the block when you push it up the incline, is that some charges in your hand push off other charges in the block. London forces (both repulsive and attractive) are electromagnetic. Contact forces between objects are electrical forces with shorter ranges, rather like the nuclear force is the strong force with a shorter range. But in the end (in both cases), it's the same force. We have different articles for nuclear force and strong force but we do take care to make it clear that they are the same thing with a different range-manifestation. SBHarris 20:08, 19 January 2012 (UTC)

• Work (thermodynamics) seems best to me because it is most inline with precedent and the least confusing option. Blue Rasberry (talk) 16:38, 20 January 2012 (UTC)

• As noted elsewhere I think we should just direct work directly to a dab page as we do mercury. The various kinds of work as defined in science are work (physics) which is force times distance for any of the basic forces of nature, work (mechanical) not universally defined, but tends to be force*distance, where the "force" is a contact force (friction, etc), work (electrical) where the force is the long-range static electric force, or an electrical field on a conductor, work (thermodynamics), where not only force times distance, but any method of increasing internal energy of an object or system except heating it is considered to be adding "work" (including adding chemical potential and even massive particles to a system), and so on.

  These are all different concepts and need their own pages. In the work (physics) page you can mention that any force times distance type work qualifies, and then go through the 4 forces, with things like work (electrical) as sub/main articles. But work (thermodynamics) is not a variety of work (physics) (rather it's the other way around) so each of these articles will have to (briefly) mention the other. SBHarris 18:05, 20 January 2012 (UTC)

• Support either as nom or Work (thermodynamics), either of whcih is much better than the present name. Peterkingiron (talk) 15:27, 21 January 2012 (UTC)
• Support – the current version is not so common, as shown in books n-grams. Dicklyon (talk) 08:41, 24 January 2012 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Mechanical forms of work

The section on Mechanical forms of work would fit better in Work_(physics) Nobody Ent 12:28, 11 July 2012 (UTC)

• I agree! There are four sub-sections related to Mechanical work - "Shaft work", "Spring work" etc. I have made them subordinate to the heading "Mechanical work". All of it belongs in Work (physics) rather than Work (thermodynamics). Dolphin (t) 12:46, 11 July 2012 (UTC)
• It's fine that there is an article Work (physics), as full and detailed as may be appropriate; go for it. But I am not a one-size-fits-all fellow. I think a careful treatment of work is also separately valuable for thermodynamics; thermodynamic work is not necessarily the same as work in general for physics. Therefore I am opposed to taking the careful and appropriately detailed treatment of mechanical work out of the article Work (thermodynamics).Chjoaygame (talk) 07:10, 13 July 2012 (UTC)
• The arrangment of the article can still be improved, I think. For example, I see pressure-volume work as a form of mechanical work. The account of pressure-volume work is faulty when it says that such work comes from volume change without right there explicitly tying it to the external force exerted during the change. The statement that any energy transfer that is not a heat transfer is a work transfer is sound for closed systems, but for open systems things may not be so simple. I suppose still other improvements are possible.Chjoaygame (talk) 07:21, 13 July 2012 (UTC)
• I think the examples should stay here, but we need to rewrite the examples (and the rest of the aricle for that matter) to make it clear that thermodynamic work is "macroscopic work" involving ensemble averages. Currently we say nothing about this, and then you don't see the formal difference between those examples and mechanical work. While the article now says that thermodynamic work is more general, that's only true in practice. In theory, mechanical work is more general, because it also includes (in theory) microscopic work that will vanish under the radar in thermodynamics and be accounted for as heat transfer. Count Iblis (talk) 15:24, 13 July 2012 (UTC)

own research re-write of lead is wrong

Editor Kbrose has taken it upon himself to re-write the lead according to his own-research unsourced notion of work. He has simply left the previous sources in place without offering new sources for his re-write. Nearly all of those sources were originally supplied by me, and I have a fair idea of what they say. (I have to say that some time ago, I had read less than I have read now, and I then, as Editor Kbrose now, believed that there was such a physical process as one that transferred energy as "chemical work". My subsequent further and closer reading has disabused me of my former error; largely, the version of the lead which Editor Kbrose has now produced has simply reverted to my former erroneous version.) We have no strong reason to suppose that Editor Kbrose has read any of the sources. Most concerning is his assertion of a concept of "chemical work" without offering any new source for it. All actual physically occurring chemical reactions are irreversible and and dissipative. Only the mathematical fiction of a quasi-static chemical change can be regarded as a reversible form of chemical reaction which would make it eligible as a form of theoretical though not physical work. Thus the notion of "chemical work" is wrong in physics. Editor Kbrose's adding of the notion of "chemical work" to the list of kinds of work destroys the basic logical structure of classical thermodynamics, however pleasing the notion might be to Editor Kbrose. There is no mention of "chemical work" in the usual textbook treatments of heat and work. It is true that some writers talk of it, but they are not concerned with the logical development of thermodynamics. Though Gibbs invented the idea of the chemical potential, his thermodynamics does not rely on the concept of work, because it is designed to deal with open systems, for which work is not defined. One might say that the new edit is overruling Gibbs by Kbrose's own research, unsourced. It may give some hint of how things are, that Kbrose's radical re-write was posted with not a word from him on this talk page on its radical nature. I vaguely recall previous editorial events and I do not have time or inclination to embroil myself in such things on this occasion. I will content myself here with noting that I think Kbrose's re-write of the lead is radically wrong and destructive of the version which it replaced; I have given above some reason for my view.Chjoaygame (talk) 08:21, 12 April 2013 (UTC)

There are other faults in the destructive re-write of the initial part of the the lead by Editor Kbrose. It talks very smoothly of conjugate constraint variable pairs, but usually such pairs are properties of the system, not of the surroundings. One thinks of formulas of the form as contributions to the work, where x and X denote for example the pressure in the system and the volume of the system. The smooth talking edit gives no hint of how this accounts for isochoric work, which is not even mentioned in the re-written section, which purports to give a general account. Isochoric work must also be accounted for by processes in the surrounds. It seems that the re-written section did not trouble itself to clarify this.

Another fault in the re-written section is the apparent attribution of radiation to momentum: "other simply mechanical constraints[6], including momental[4], as in radiative transfer." This is nonsense on the face of it. It would be hard to explain this except by assuming that it means that the editor did not even bother to read the titles of the references that are cited there, let alone thinking about their meaning. I gave a reason above why I do not intend to try to remedy this destructive re-write.Chjoaygame (talk) 13:36, 12 April 2013 (UTC)

A futher fault, indeed a reprehensible error, in the re-write is that it says that "It is customary to calculate the amount of energy transferred as work through quantities external to the system of interest." No, it is not merely customary to do so; it is obligatory. To say that it is customary is to suggest that it is only customary. The reasons why it is obligatory are so familiar and well known that I should not need to recite them here. Some recent recitations of some the reasons may be found here. Again, I leave it to others to correct this defective new version for reasons I have given above.Chjoaygame (talk) 21:35, 12 April 2013 (UTC)

Could I ask you to moderate the tone of this discussion? Kbrose's edits appear as a good-faith attempt to improve the article, and should not be described as "radically wrong", "destructive", "smooth talking", "nonsense" "reprehensible" and "defective". It is preferable to use language such as "I believe that the statement ... is incorrect because ..., as explained in [Reference and page]." Pretend your comments are to be refereed.

Some points at issue are quite deep and have been debated for decades in the thermodynamic literature. I have taught physical chemistry and chemical thermodynamics, but cannot say who is actually correct without much reflexion and reading. So perhaps some of the litigious points should actually be addressed in the article. For example, a Google search for "chemical work" + thermodynamics gives 11400 hits, even if there may be a more recent consensus to abandon this concept. You said above (if I interpret correctly) that you used to believe in processes doing "chemical work" but have since realized this description to be an error. I suggest that it would be more useful to the reader to mention that this concept does appear in (especially older) literature, and to explain why it is preferable not to think that way. Similarly for some of the other points.

Yes, it takes more time to discuss everything properly, with proper references. So sometimes we have to accept someone else's way until we have time to marshal our arguments. There is chemistry content on Wikipedia which I believe to be incorrect, but do not have time to address properly. I accept this situation as part of the nature of a collective project.

As they would say where I live, plus de calme et de respect s.v.p.Dirac66 (talk) 22:29, 14 April 2013 (UTC)

When Chjoaygame made his first complaints here on this Talk page I left a message for Kbrose, alerting him to this new thread and asking him to join the discussion - see my diff. Kbrose has not edited on Wikipedia since 12 April so it is likely he hasn't yet seen either my message on his Talk page or Chjoaygame's comments on this Talk page.

Chjoaygame has alleged that after he (Chjoaygame) wrote statements in the article and added in-line citations to support his statements, Kbrose significantly altered those statements but left the in-line citations unchanged, giving readers the impression that Kbrose's statements are supported by Chjoaygame's in-line citations. This will always be a controversial action so it is important that Kbrose should join this discussion and give us his view of the situation. Dolphin (t) 06:32, 15 April 2013 (UTC)

If one accepts the notion that thermodynamic work is a generalized framework over that used in mechanics then it makes no sense to arbitrarily exclude chemical processes. After all, it is in chemistry where thermodynamics has its broadest applications. The literature is full of chemical work examples, but all forms cannot always be found mentioned in all primary sources, as even primary sources tend to be opinionated one way or another depending on the mood of the period or the experience and interest of the authors. Writing about these matters in a neutral objective fashion is not easy and requires a fairly broad overview and understanding of the history of science and the various flavors or philosophies of chemical and physics teaching. In particular these subject matters and historical conflicts cannot be treated in detail in the space allotted for WP articles, nor is it desirable. In addition, the WP authors here who presently try to put their spin on these articles are poorly qualified to make these judgements. They narrowly (try to) interpret specific references, without regards to larger context and historical science evolution, or even without sufficient subject matter knowledge. Instead minute points are endlessly debated with wrong arguments and misunderstanding. Debating them is a waste of time, as nothing is ever gained. These are endless circular debates that only illustrate the incompetence of these editors. Some of them do not want to accept contemporary definitions of concepts and try to infuse these articles with their own wrong versions of physics.

The discrimination of physics vs. chemistry is anachronistic and unsustainable in modern teaching and the artificial differentiation in WP of "work (thermodynamic)" and "work (physics)" is a WP invention and wrong. Thermodynamics is physics too. If anything, the article "work (physics)" should be called "mechanical work", and the extensive treatment of mechanical work in this article should be removed, as this article should concentrate on the theoretical generalizations in thermodynamics, best the articles should be merged, as work in physics takes many forms as it does in chemistry.

RE: accusation by these authors: frankly WHO CARES? these statements are not worth responding to. It only leads to more never ending circular nonsense. It is no surprise that WP articles are shunned in education as reference or learning material and rarely does one find a reputable scientist wanting to engage with these WP editors. It is just such a pity that a work like WP cannot produce somewhat reliable science material. Ok, a couple editors here did care, thank you, for trying to bring some sense into it. Kbrose (talk) 06:13, 16 April 2013 (UTC)

I would suggest to do things more rigorously as I suggested last year in the last comment of the previous section. We now deviate from almost all modern textbooks by omitting "macroscopic" from "macroscopic work", we don't mention the need to have an ensemble over which you must average to define this. Once you follow the modern approach rigorously, you don't get these sorts of problems as discussed here. By not doing this, we fail to communicate what is the most relevant to say about this subject, i.e. that in the end you are dealing with a system consisting of many molecules, thermodynamics is simply what you get when you attempt to give a coarse grained description of this in terms of coarse grained variables (e.g. the total internal energy, the macroscopic boundaries of the system). Then, you can't always have a fully closed description in terms of only the macroscopic variables, e.g. energy can leak into the miscroscopic variables we average over, which must then be accounted for as "heat".

You then won't get these disputes about e.g. "chemical work"; once you have a macroscopic thermodynamic description of a system with different types of molecules, it is well defined. The only valid arguments will always be about the way one gives a macroscopic thermodynamic description of a system. In principle there are no real processes during which a thermodynamic description is possible, but you always consider well defined initial and final thermal equilibrium states. That's why Reif says that thermodynamics is a misnomer, the subject should have been called thermostatics. Count Iblis (talk) 12:28, 16 April 2013 (UTC)

Mechanical work, surface tension, electrochemical work

Today's edit by Kbrose removed the entire section labelled "mechanical work". As a physical chemist I agree that shaft work, spring work and elastic solid bars have little relevance to thermodynamics. I would however retain the last part about Work associated with the stretching of liquid film, since surface tension is a fundamental thermodynamic property of liquids which is of interest to chemists. May I reinsert this subsection into the article?

Also, one important category which seems absent is electrochemical work performed by (or on) cells (or batteries), which is essential to understanding redox reactions. How about a brief section on electrochemical work and the Nernst equation? Dirac66 (talk) 23:21, 16 April 2013 (UTC)

Well, the nature of surface tension is completely analogous to that of a spring or an elastic rubber band or elastic bar, and the equations that describe it are identical and the underlying physical phenomena are the same as for any elastic material. It's just that the field has its own name for the forces and variables, but there is nothing particularly 'thermodynamic' about the elastic behavior. But if there is some reason based on thermodynamics, in connection with the first law, to include it, I have no strong objections. I would agree that a section about electrochemical work would be highly relevant. Kbrose (talk) 04:52, 17 April 2013 (UTC)

You can e.g. easily explain the counterintuitive temperature dependence of the elasticity of a rubber band using a simple model. Count Iblis (talk) 13:31, 17 April 2013 (UTC)

This last point is mentioned at Rubber elasticity#Thermodynamics. Dirac66 (talk) 18:51, 17 April 2013 (UTC)

That aside, it was never the attempt in the deleted sections to explain the temperature dependence of elastic behavior or surface tension using thermodynamic considerations. Of course, such considerations are applicable to elasticity in solids too, as for any spring, and indeed thermodynamics & statistical mechanics are of great importance in supplying the partition functions for the phonon density of states used to arrive at models of elasticity. Indeed that should be discussed in the relevant topic pages. The section here only dealt with the spring-like mechanical behavior on a macroscopic level and therefore fits into mechanics better. This page should rather deal with the macroscopically 'non-mechanical' thermodynamic types of work. If one drills down far enough toward the fundamental forces of nature, then everything seems more and more like mechanical springs, only the cause of spring-action changes between gravitational, electric, magnetic, etc. At that level it might indeed be easy to forget about macroscopic character of the interaction, be it classical physics or classical chemistry. Kbrose (talk) 19:42, 17 April 2013 (UTC)

Chemical work is typically expressed as the product of a chemical potential and the amount of substance it is working on, rather analogous to a gas pressure working on its volume. Kbrose (talk) 19:59, 17 April 2013 (UTC)

Spring work and surface tension work are often considered to be reversible and are therefore reasonably regarded as thermodynamic work in the ordinary sense. Shaft work needs a little closer attention.

Joule thought that shaft work was important. It is a key concept also in Planck's version of the second law.

Moreover, Joule did not permit "chemical work" in his founding experiments.

"Chemical work" is not work proper in the strict sense of thermodynamics. It is described by variables that may be called 'generalized work variables', but they are not ordinary thermodynamic work variables. They cannot be fully controlled by mechanical work in the surroundings. The reason is that chemical reactions that occur in nature are essentially irreversible. The important idea of work in the basic principles of thermodynamics is that it is considered in effect to be potentially reversible when supplied by the surroundings, which is the proper place to estimate its quantity. Natural transfer of energy as heat is irreversible.

It is true that shaft work done on the system is usually irreversible, but it is considered to be supplied by a reversible source in the surroundings; the irreversibility is considered to arise by friction or viscous drag entirely within the system. A system can to electrical work on its surrounds and the surrounds can to electrical work on the system. But if this involves chemical change in the system, it is irreversible. A charged battery that is capable of doing electrical work on its surrounds is not a system in its own internal state of thermodynamic equilibrium, and is therefore not a thermodynamic system in the strict classical sense, which requires that it be in its own internal state of thermodynamic equilibrium. A physically real battery when isolated always eventually discharges itself internally.

While it sounds smooth and sophisticated and modern and advanced and systematic to label "chemical work" as if it were thermodynamic work proper, to do so hides the most basic principles of thermodynamics. It is not good for the Wikipedia to hide the most basic principles of thermodynamics. It is no remedy to confound electrical work with chemical change by talking of "electrochemical work".

There is a kind of reason here. dU = T dS + P dV + μ dN tells the story. A system can be arranged so that each of the terms there is determined physically independently under certain conditions. For example the container may have three walls; one rigid and impermeable to matter, but diathermic; one adiabatic; and one rigid but permeable to matter. In a useful sense, the diathermal wall passes only heat, the adiabatic wall passes only work, and the internal energy that passes through the rigid permeable wall cannot be uniquely resolved into work and heat components. The internal energy that passes through the rigid permeable wall therefore earns its place as a separate term in this formula. To call it a "generalized work" term is smooth and sounds sophisticated, but it hides its fundamental importance as a separate kind of transfer of energy.

These principles are not stated in advance in most student text presentations. That is to say, in the introductory presentation, work and heat are treated simply for closed systems, without comment on why the treatment restricts itself to them, and refers only to closed systems. Much detail is considered at this stage, and important principles are set forth.

This is easy to read as merely pedagogical, to make it easy for the student, without confusing him with the added detail of transfer of matter.

And then, later in the text, the transfer of matter is treated. It is easy to read this as if it were a simple generalization of the closed system.

It is simple, but not utterly simple. It was not just a pedagogical device. There was important physics in it. It only works if the matter transfer is done through a path that is independent of the already previously considered work and heat transfer paths. It was Born who made this clearest, but other top people agree.

These facts are important for a proper understanding of thermodynamics, and Wikipedia should not hide them.Chjoaygame (talk) 04:08, 2 January 2014 (UTC)Chjoaygame (talk) 09:11, 2 January 2014 (UTC)

work and heat and transfer of internal energy

It is unfortunate that the words work, heat, and internal energy can be confounded. The present lead of the article does that. There are historical reasons for this problem.

In the early days of thermodynamics, Clausius talked of "internal work". That concept is sometimes nowadays also referred to as "unavailable work". The Clausius usage more or less persists in this latter-day form. In present-day language, it refers to work which is supplied by a source in the surroundings of the system, but is manifest within the system at the end of the process as undifferentiated internal energy, not as remanent change in some generalized coordinates of the system such as pressure and volume exactly matching the externally supplied work. The point is that for the sound theory of thermodynamics, work is defined not by changes in the state variables of the system, but, rather, by changes in the surroundings. The idea is that for the description of process, the thermodynamic system itself is treated as a black box, avoiding mention of its internal workings and mechanisms. The mechanisms of the surroundings are considered suitable for detailed description, not just black-box summary.

An example of this problem is to be found in non-equilibrium thermodynamics. The energy associated with a transfer of matter cannot be uniquely split into heat and work components. Nevertheless there is true thermodynamic quantity associated with transfer. Some authors call it heat of transport,<Tschoegl, N.W. (2000). Fundamentals of Equilibrium and Steady-State Thermodynamics, Elsevier, Amsterdam, ISBN 0-444-50426-5, p. 209.> while others refer to work of mass transfer.<Eu, B.C. (2002). Generalized Thermodynamics. The Thermodynamics of Irreversible Processes and Generalized Hydrodynamics, Kluwer Academic Publishers, Dordrecht, ISBN 1-4020-0788-4, p. 26.> The latter author is an unashamed user of many of Clausius' definitions, and an inventor of a new term for his own purposes "calortropy".

My view is that this problem is best dealt with in these pages by consistent use of the term internal energy to refer to the energy associated with transfer of matter.

Eu also speaks of as "work" what I think would be better referred to as energy of process when Eu is talking about chemical reactions, and in other contexts. As I have mentioned just above, Eu is a little idiosyncratic in his terminology. Since natural chemical reactions are always irreversible, it is likely to confuse readers to speak of its energy as "work". Work in the surroundings is often considered by thermodynamic convention as able to be performed reversibly, contrary to nature.

Thermodynamic work supplied by the surroundings is naturally not stored in the system entirely as available work, the so-called "work of the task". Thermodynamic work supplied by the surroundings is in natural processes partly converted into internal energy in the system that cannot be recovered without special changes in the surroundings. That part is Clausius' "internal work". In present-day terminology, its storage is described by the state variable internal energy, and in present-day terminology is it not stored as work in the system. Work is a process variable.

Some people like to use the term generalized to refer to kinds of thermodynamic work. This can be confusing and harmful for those not at home with the specialized jargon. The problem partly arises because of the term 'generalized work variable'. The base case for thermodynamic work is pressure-volume work. An electric field imposed from outside the system also does work on the system, and this leads it to be termed a 'generalized work variable'. Then the drift of terminology goes to any extensive variable that has a conjugate intensive variable, such as mole number, and all are lumped as "generalized work variables". An easy slip down a bad path.

I think the best and clearest way for Wikipedia thermodynamics articles is to stay with the simplest definition of work as supplied by a source in the surroundings, which may be a reversible source. Heat is transferred without work or matter transfer. Other transfers of internal energy are transfers of internal energy.

For statistical mechanics, thermodynamic work can be supplied by externally imposed changes in the set-up of the system, such as changes in volume or length, that are manifest as remanent changes in the energy levels of the system. Thermodynamic work can also be supplied by rapid motion of the system that is eventually left with its original volume or length and original energy levels unchanged, though the occupation numbers were changed permanently during the process. Clausius would call this 'internal work'. Clausius would also say that it heated the system, but it is not heat transfer as defined in present-day thermodynamics.Chjoaygame (talk) 18:29, 1 April 2014 (UTC)

work or generalized 'work'

I would like to propose a change to the present article.

I think the definition of "work" that heads the present article is more safely regarded as a definition of 'generalized work'. It reads:

In thermodynamics, work performed by a system is the energy transferred by the system to another that is accounted for by changes in the external generalized mechanical constraints on the system. As such, thermodynamic work is a generalization of the concept of mechanical work in physics.

My reason is that the concept of mechanical work in physics is fundamental and primitive, presupposed for thermodynamics as expounded since 1909. It is potentially confusing to replace it with a concept of 'generalized work'. I think it safer to say distinctly and explicitly that 'generalized work' is a generalization of work.

It is foundational to the exposition of thermodynamics that work can be said to done by a system or working substance and that the amount is counted in the surroundings as delivered macroscopically without dissipation. This is more of a theoretical postulate than a description of practical experience. But it is a postulate that is needed for a convenient theoretical development. I don't think I can mount a better argument than this.

In particular, so-called "chemical work" is, I propose, best regarded as a kind of generalized work. Physically it goes on at the molecular level, not directly as macroscopically observable mechanical work such as is envisaged in the foundational exposition. I regard that as essential to the nature of chemical work. Something that happens at the molecular level is vulnerable to the vagaries of the second law.

My reference this is, I think, sufficient. According to Prigogine & Defay, the system's chemical reactions themselves (except for the special limiting case in which in they are driven through devices in the surroundings so as to occur along a line of thermodynamic equilibrium) are always irreversible and do not directly interact with the surroundings of the system.

Chjoaygame (talk) 01:42, 2 September 2015 (UTC)

No reply?

It is evident that people like to use the concept of generalized work, to include all state variables other than temperature regarded as measuring quasi-static heat transfer. I would like to suggest that generalized work here be called generalized work, while work is called work, and defined as proposed, for example, by Haase, and by Münster, as cited here below at response 2.Chjoaygame (talk) 12:17, 5 September 2015 (UTC)

I note that your excerpts from Haase and Münster do not actually use the term generalized work, and also that a Google search for "generalized work" "thermodynamics" does not yield very many results. I believe that Wikipedia should not introduce such a short terms unless it is common in the literature, as we may mislead readers into thinking that this is a standard term. It would be better to say "a generalized concept of work", which is longer and less precise (here a virtue!) so that readers will realize it is an explanation rather than a standard term. Unless of course you can find a few sources which do talk about generalized work. Dirac66 (talk) 19:34, 5 September 2015 (UTC)

A fair point. Gratefully received. Yes, you are right. Tisza has a section entitled 'Generalized work', pages 88–92, in his account of his MTE (macroscopic thermodynamics of equilibrium). On page 88 he starts:

The role of work in MTE is of fundamental importance. This apparently simple concept also has many ramifications, some of which are very complex.

Tisza is perhaps a little recondite for the present purposes. This at last sorts out my puzzlement about this matter.

There is a usage, "chemical work", a non-telescoped term for the non-mechanical part of generalized work, introduced by Gibbs. It is used by Silbey, Alberty, & Bawendi, initially with quotation marks on page 103, but a second time without them on page 127. When they define work on page 31, meaning mechanical work, they put the word in bold font, not in quotation marks. Routinely, they use bold font to define terms. Likewise, on page 36, Callen writes "We shall call Σ_j μ_j dN_j the quasi-static chemical work."

Looking through Prigogine & Defay, I did not see them use either term, 'chemical work' or 'generalized work', or use the term 'work' as a telescoped form.

I have not been too successful in finding clear examples of the use of 'work' to mean generalized work. Perhaps I have looked in the wrong places?

Slightly changing the subject, this is relevant to the salvaging question discussed below. Callen on page 103 writes:

The repository system into which work is delivered is called a "reversible work source". Reversible work sources are defined as systems enclosed by adiabatic impermeable walls and characterized by relaxation times sufficiently short that all processes within them are essentially quasi-static. From the thermodynamic point of view, the "conservative" (nonfrictional) systems considered in the theory of mechanics are reversible work sources.

He goes on to define reversible heat sources.

Your proposed wording is very helpful, I think.Chjoaygame (talk) 23:27, 5 September 2015 (UTC)

I have checked the reference cited for the claim that radiative transfer can be called work. The reference says that radiation can at times need to be considered as a component of a system, but does not suggest that radiative transfer can be called work. Accordingly I have removed radiation from the list of forms of work. It was a mistake to put it there in the first place.Chjoaygame (talk) 08:28, 7 September 2015 (UTC)

over-zealous undo

This undo, by Editor Melmann was on the whole deleterious. It seems to have relied on an automated algorithm that demanded citation of reliable sourcing, but did not otherwise evaluate the edits that it undid.

The undone edits had merit. In particular, they removed a demand for reversibility. For the formulas involved, indeed reversibility is NOT a requirement. Removal of the demand was right. Also, they distinctly improved the wording that described the formulas.

It would be good if good quality (not mediocre) reliable sources were cited for the edits. Their current absence is undesirable, but, I think, not reason enough to undo them.

I am undoing the undo.Chjoaygame (talk) 12:11, 3 September 2015 (UTC)

Mentioned contributions do not appear to comply with WP:SOURCE. I'd encourage you to re-read that. It needs to be immediately apparant where this information is from and why it should be trusted; linked contributions lacked that.--Melmann^(talk) 12:17, 3 September 2015 (UTC)

Following your admonition, I read "All material in Wikipedia mainspace, including everything in articles, lists and captions, must be verifiable. All quotations, and any material whose verifiability has been challenged or is likely to be challenged, must include an inline citation that directly supports the material. Any material that needs a source but does not have one may be removed. Please remove contentious material about living people that is unsourced or poorly sourced immediately."Chjoaygame (talk) 13:01, 3 September 2015 (UTC)

Though I would rather have seen Editor Hnedkovl or Supervisor Melmann do it, I have supplied references, in order to remove grounds for further chatter.Chjoaygame (talk) 18:05, 3 September 2015 (UTC)

I have followed this up, and made further edits. Indeed the edits were faulty and needed correction and references. For the formulas used, reversibility IS a requirement; my mistake. I have given the reason for this requirement.Chjoaygame (talk) 23:36, 5 September 2015 (UTC)

Can faulty edit be salvaged?

Two days ago editor Chjoaygame deleted the following as a "faulty IP edit": Work is said to be done by a system if , its sole effect on the things external to the sourroundings is reduced to raising of the weight.

I agree that the deleted edit as written is fundamentally faulty (in addition to linguistically faulty) because there are other types of work besides raising weights, such as electrical work and many other types mentioned in the article.

However this edit reminds me of a more correct statement, and a quick Google search yielded the version here, where the definition of work is written: Work is done by a system on the surroundings if the sole effect on everything external to the system could have been raising a weight. As briefly explained further down on the Learnthermo website in the section Ch 4, Lesson A, Page 2 - The Thermodynamic Definition of Work, the key words are could have been. I also remember reading the key words somewhere else as can be (completely) converted into; for example the electrical work of charging a battery can be completely converted into the work of raising a weight by an electric motor. This distinguishes work from heat which by the Second Law can only be partially converted into the work of raising a weight.

This idea seems to be missing from the article, and I would like to suggest that the article should include a rewritten version including the idea of potential (and not necessarily actual) conversion to the raising of a weight, as well as a more authoritative source if possible. Do others agree? Dirac66 (talk) 01:07, 4 September 2015 (UTC)

response 1

Editor Dirac66 raises an important matter.

He is concerned, as I read it, about a distinction between work defined rather directly and simply, and work defined more indirectly and I would say more complicatedly. By direct and simple I mean that the system must deliver its work as a macroscopic force felt immediately by the surroundings. What happens further in the surroundings can be analyzed further when one has sorted out the concepts needed to describe the adventures of the system. A question may arise of whether the flow of electrons is a transfer of matter. I am inclined, at least for the present, to think that to escape being considered as a transfer of matter it should result in no net transfer of charge.

I am not sure where the proposal to define in terms of raising a weight comes from. I have read it in some texts that I find clever and self-confident but not too convincing. I think it is an attempt to create concreteness, but that it goes too far.

The questions arise in considering the adventures of the transferred energy in question as it occurs in the surroundings. I distinguish this from its adventures in the system. He emphasizes the phrase could have been.

Perhaps this is a way of talking about a distinction between work in the direct and simple sense, and what may be called 'generalized work'.

Editor Dirac66 writes "for example the electrical work of charging a battery can be completely converted into the work of raising a weight by an electric motor." This does not explicitly distinguish the system from the surroundings. It is not clear to me whether the battery or the motor is in the system or in the surroundings.

There may be a problem with defining things in terms of "the raising of a weight". It presupposes gravity acting on the weight. It may not be easy to arrange that the system be exempt from gravity while the surroundings have it. We have recently had some questions about whether the second law can be stated for systems in the presence of an external field. Part of the problem is the desire to jump in theory to continuously distributed inhomogeneous systems before homogeneous systems have been settled. I have carefully read the committee report, written by Alberty, cited by a certain redoubtable editor. I have further carefully read a major text by Alberty and others. My conclusion is that our redoubtable editor is not rightly reading Alberty.

I am not too sure about an authoritative source. There are very many more or less reliable sources. If there are significant differences among them then the question of Wikipedia point-of-view multiplicity may arise. Which, if any, is more authoritative? I think we ought to try to analyze and distill the best, at least as a first approach.

I think it most important that the more concrete and simple definition be given a good run, because of its fundamental place in the basic logic of the subject. Charging a battery is a chemical process and according to Prigogine and Defay, as I read them, is not in general reversible.

Another fundamental point that I think needs a good run is the distinction between the total energy of a system and its internal energy. The total energy is very often representable as the sum of three terms, the internal energy of the system, its kinetic energy as a whole, and its potential energy as a whole, obviously with respect to some externally imposed force field.

I think it important that the basic concepts be defined strictly in macroscopic terms, not relying on continuous field pictures of the system's internal content, expressed in internally spatial differential equations. The internal spatial differential equation approach should be derived from the macroscopic approach. The internal spatial differential equation approach is not good for an introduction in any case.

I suppose that further discussion may arise.Chjoaygame (talk) 05:30, 4 September 2015 (UTC)

Having babbled airily about basic foundations, perhaps I ought to say more explicitly what I intend by that.

First we settle the system with respect to its surroundings, as to its velocity and attendant kinetic energy as a whole, and as to its position and potential energy as a whole. The remainder of its total energy is the internal energy.

Next, the internal energy is determined for a closed system, that is to say, for which matter transfer is not allowed by its walls. We further require processes that do not involve transfer of energy as heat. The system has adiabatic walls as its only dealing. All that is left are transfers as work. There is very strong opinion here that this is the foundational reasoning. This is why I think work should be treated very carefully.

Next we allow also transfer as heat, still forbidding transfer of matter. Thus we determine the mechanical equivalent of heat, and we use only mechanical units.

Next we allow also transfer of matter, through walls spatially and otherwise separate from those that allow the transfer as heat and work but not matter. We forbid heat and work transfers, and allowing transfer of matter we have only ΔU₁ + ΔU₂ = 0. Now it's time to be very careful indeed about our reference states, and we can find the amount of energy transferred in company with matter transfer, not uniquely resolvable into heat and work transfers.

As for the general setting. It doesn't matter in what order are the postulates are listed. It's all the postulates at once, or go back to the drawing board. One of the postulates in the established view is conservation of energy. The existence of adiabatic walls is also foundationally postulated in the established view. But the sequence in which the postulates are called upon in argumentative presentation does matter and is open to opinion while still not trying to alter the basic postulates.Chjoaygame (talk) 08:13, 4 September 2015 (UTC)

Thank you for your replies. I see that the question is much more complex than I had thought. So I decided to check the introduction of work in some thermodynamics books and have now spent an hour in my university library, in order to align my thoughts with reliable sources. Most of the books I checked just introduce work more or less as the current article does, sometimes with the addition of an equation such as dW = Σ X_i dx_i (X = constraint, x = coordinate). However I did find 4 from the 1960's and 1970's (see list below), which do mention that other forms of work can be converted to the work of raising a weight, so the idea is out there where students may encounter it (as on the above cited website), and I think it should be mentioned somewhere in the article. Certainly not at the top of the article as in the faulty edit deleted 3 days ago, and not as the definition of work; instead I now suggest a section at the end of the article titled perhaps Conversion between different forms of work,. We could point out that all the other mechanical and non-mechanical forms of work are considered equivalent to the original form of lifting a weight, because they can be converted 100% (in principle at least) into this form of work, as opposed to heat which is limited to the Carnot efficiency. And we can mention that some authors have considered this a defining characteristic of work.

Re systems vs. surroundings for battery and motor. I would consider that if a system is used to charge a battery, then the battery is part of the surroundings of that system. And if the battery subsequently operates a motor which lifts a weight, the motor and weight are not part of the original charging system so they are also in the surroundings.

Re gravity acting on the weight - the texts I consulted seem to just assume that the weight is in a gravitational field. And the system presumably is in the same field but this does not seem to matter.

Finally the 4 books which mention that all work could be converted into the lifting of a weight are: 1) F.C.Andrews Thermodynamics: Principles and Applications (Wiley-Interscience 1971), p.17-18 ISBN 0-471-03183-6. 2) K.Denbigh The Principles of Chemical Equilibrium (Cambridge University Press 1st ed. 1955, reprinted 1964), p.14. 3) J.Kestin A Course in Thermodynamics (Blaisdell Publishing 1966), p.121. 4) M.A.Saad Thermodynamics for Engineers (Prentice-Hall 1966) p.45-46. Dirac66 (talk) 20:09, 4 September 2015 (UTC)

response 2

Thank you for your response.

Denbigh and Kestin ring bells for me, but I need to go to the library to get them.

As a very loose and vague statement, open to immediate change or denial, perhaps one might say that what happens in the surroundings is less scrutinized than what happens in the system. Very loosely thinking, perhaps one might say that work done on the surroundings is allowed to be done on ideal work transducers, as a matter of convention? This would create problems for some statements of the second law, I think? I would think it a mistake to allow the battery as an ideal work transducer because it happens by chemical reactions, which are irreversible, because they change many disorganized single ions or molecules, not obviously macroscopic items.

Haase has a section on work on pages 19–24. Amongst other things he says that P dV is not an exact differential, which I think may show that I was wrong to allow a recent edit that removed a caveat that required reversibility. Haase in that section cites only Guggenheim and Callen. He writes as follows on page 20.

If a system or part of a system undergoes a displacement under the action of a force, the work done on the system [his sign convention makes that positive when it adds to system internal energy] is the integral over the product of the force and the component of the infinitesimal displacement parallel to the force. This definition, already familiar in mechanics and electrodynamics, will be used here, too. But it should be noted that only work involving an interaction between the system and its surroundings is significant in thermodynamics. Thus, the forces to be considered are macroscopic and do not include forces acting internally between different parts of the system. The forces may be of mechanical, electric, or magnetic origin.

No explicit mention of gravity there. Perhaps that is a weakness in his presentation? He explicitly restricts the section to refer only to closed systems.

More to think about here. Need some time.Chjoaygame (talk) 01:48, 5 September 2015 (UTC)

Not much luck right now in library. Denbigh: two editions out on loan, one in Engineering Store, one in General Store. Kestin: in Engineering Store. All take days or weeks to get. Andrews and Saad not held.Chjoaygame (talk) 04:36, 5 September 2015 (UTC)

An extract from the present article:

History

1824

Work, i.e. "weight lifted through a height", was originally defined in 1824 by Sadi Carnot in his famous paper Reflections on the Motive Power of Fire, he used the term motive power. Specifically, according to Carnot:

We use here motive power to express the useful effect that a motor is capable of producing. This effect can always be likened to the elevation of a weight to a certain height. It has, as we know, as a measure, the product of the weight multiplied by the height to which it is raised.

Joule's apparatus for measuring the mechanical equivalent of heat.

1845

In 1845, the English physicist James Joule wrote a paper On the mechanical equivalent of heat for the British Association meeting in Cambridge. In this paper, he reported his best-known experiment, in which the mechanical power released through the action of a "weight falling through a height" was used to turn a paddle-wheel in an insulated barrel of water.

In this experiment, the friction and agitation of the paddle-wheel on the body of water caused heat to be generated which, in turn, increased the temperature of water. Both the temperature change ∆T of the water and the height of the fall ∆h of the weight mg were recorded. Using these values, Joule was able to determine the mechanical equivalent of heat. Joule estimated a mechanical equivalent of heat to be 819 ft•lbf/Btu (4.41 J/cal). The modern day definitions of heat, work, temperature, and energy all have connection to this experiment.

This may partly address our present concerns.

An extract from Callen:

Restricting our attention to thermodynamic simple systems, the quasi-static work is associated with a change in volume and is given quantitatively by

đW_M = − P dV                                                (1.1)

where P is the pressure. In recalling this equation from mechanics, we stress that the equation applies only to quasi-static processes. ... If the piston is pushed in very rapidly, the gas immediately behind the piston acquires kinetic energy and is set into turbulent motion and the pressure is not well defined. In such a case, the work done on the system is not quasi-static and is not given by equation (1.1). ...

So I was wrong to let that edit through. I will shortly fix it.

Münster has little to say about work immediately relevant to the weight-lifting thing. He writes:

Carathéodory's theory formulates the First Law from a viewpoint different from that of the classical theory. Internal energy is introduced by means of purely mechanical concepts ...

... for homogeneous systems, we have for a quasi-static process

dW = − P dV                                                (8.4)

in agreement with Callen.Chjoaygame (talk) 09:03, 5 September 2015 (UTC)

On page 31, Silbey, Alberty, & Bawendi write "Work is often conveniently measured by the lifting or falling of masses."Chjoaygame (talk) 23:16, 5 September 2015 (UTC)

Excellent, a newer source than the abovementioned, 4th edition 2004 or 2005 on the site I found. And I think it would be reasonable to read their sentence as "All forms of work are often ..." or "Other forms of work are often ..." Dirac66 (talk) 23:36, 5 September 2015 (UTC)

I cited S, A, & B above as of the 4th edition, 2005. I ought to have cited it again here. That is what I was quoting. I am not clear exactly what you mean by "All forms of work".Chjoaygame (talk) 23:48, 5 September 2015 (UTC)

Basically I mean the other forms listed in the article, in the sections Other mechanical forms of work and Non-mechanical forms of work. A clearer phrase might be All forms of thermodynamic work, to exclude what is called work in everyday life but has nothing to do with thermodynamics.Dirac66 (talk) 01:35, 6 September 2015 (UTC)

response 3

Thank you for this reply. Looking in the article, I see quite a lot of text. Of that, I have contributed some, and perhaps some of that needs correction.

At the end of the article's text is the following:

Examples of non-mechanical work modes include

• Electrical work – where the force is defined by the surroundings' voltage (the electrical potential) and the generalized displacement is change of spatial distribution of electrical charge
• Magnetic work – where the force is defined by the surroundings' magnetic field strength and the generalized displacement is change of total magnetic dipole moment
• Electrical polarization work – where the force is defined by the surroundings' electric field strength and the generalized displacement is change of the polarization of the medium (the sum of the electric dipole moments of the molecules)
• Gravitational work – where the force is defined by the surroundings' gravitational field and the generalized displacement is change of the spatial distribution of the matter within the system.

The lead starts as follows:

In thermodynamics, work performed by a system is the energy transferred by the system to another that is accounted for by changes in the external generalized mechanical constraints on the system. As such, thermodynamic work is a generalization of the concept of mechanical work in physics.

The external generalized mechanical constraints may be chemical, electromagnetic, (including radiative), gravitational or pressure/volume or other simply mechanical constraints, including momental, as in radiative transfer. Thermodynamic work is defined to be measurable solely from knowledge of such external macroscopic constraint variables. These macroscopic variables always occur in conjugate pairs, for example pressure and volume, magnetic flux density and magnetization, mole fraction and chemical potential. In the SI system of measurement, work is measured in joules (symbol: J). The rate at which work is performed is power.

Perhaps these points have more to do with the section above on this talk page, headed work or generalized 'work', and might be further discussed there. The present section is about using lifting a weight to put work in a nutshell, as you are proposing, and I am happy about.Chjoaygame (talk) 05:45, 6 September 2015 (UTC)

luck in the library

The library responded quickly. Here follow some findings.

Denbigh 1st edition reprinted 1957

Page 14:

1.5    Work

   The notion of work is not regarded as being in need of definition in thermodynamics, since it is a concept which is already defined by the primary science of mechanics.

...

   It may be noted that all forms of work are interchangeable by the use of simple mechanical devices such as frictionless pulleys, electric motors, etc. The correct usage of the term 'work' implies that the particular type of work which is under discussion may always be expressed in terms of the raising of a weight.

The wording of the last, just previous, sentence is slightly different in the 4th edition (1981/reprint 1993).

Kestin 1966

Chapter 4, pp. 110–148.

   The concept of work in thermodynamics is a natural extension of the concept of work in mechanics. This extension is required to take into account the greater variety of phenomena encountered in thermodynamics. ...

...

4.4   The definition of work in thermodynamics

   In generalizing the preceding concept of work to include phenomena other than those encountered in mechanics, an attempt must be made to divorce it from the need to consider forces, and yet to preserve its essential physical characteristics. We can recognize the latter by rephrasing the definitions of the preceding section in thermodynamical terms. ...

...

[Discussion of the difference between raising and lowering of a weight, in terms of what could be so.]

[Discussion of reversible, irreversible, and quasistatic processes.]

[p. 130]... It is clear that all natural processes are irreversible and that reversible processes constitute convenient idealizations only.

4.8   General form of expressions for work in other reversible and quasistatic processes

   In order to establish expressions for reversible and quasistatic irreversible work for systems other than the one considered in Section 4.5, it is first necessary to study empirically their general characteristics, and to establish their equations of state ...

...It can, however, be stated at the outset that the reversible work can be represented by a single product of the form

dW = Y dZ                                                (4.26)

in the case of a system with two independent variables.

...

This similarity induces us to call all intensive properties Y which appear in the expression for elementary work by the common designation of generalized forces, whereas all extensive properties Z are known as generalized displacements. ...

It seems to me that Kestin is here talking about 'work in reversible and quasistatic processes', not the same as the phrase I proposed, 'generalized work'. I think our present article is also talking about work in reversible and quasistatic processes.

[p. 144]   The work performed by a system during a reversible process can be computed by observing the system itself, because all quantities in the expression for work can be expressed in terms of its state. In the general case, this is impossible and the interaction between the system and its surroundings must be known in detail.

This last remark is not reflected systematically in the present article.Chjoaygame (talk) 00:11, 9 September 2015 (UTC)

Perhaps my following the references has sidetracked too much from Editor Dirac66's proposal to put in a section about potential to raise a weight. Perhaps I should repeat here that I am happy with his proposal.Chjoaygame (talk) 08:32, 15 September 2015 (UTC)

OK, I have now made a start and inserted a brief final section with what I consider the essential point, based on what I suggested at the end of Response 1 above. I have not gone into all the points in the above discussion, so editor Chjoaygame or others may wish to expand the section.Dirac66 (talk) 21:02, 2 October 2015 (UTC)

If it is received as heat, it is heat

I have undone a good faith edit. The edit is over-explanatory. If the work is done on the system, it is counted as work, even if it is frictional. Some of the frictional work may be done on the surroundings, and become internal energy of the surroundings, and then pass to the system as heat; that is energy passing to the system as heat, not as work done on the system. The system does not do work as friction on the surroundings.Chjoaygame (talk) 23:39, 2 January 2016 (UTC)

Editors: Please make a choice between "Pressure–volume work" and "Pressure-volume work" (en dash versus hyphen, respectively)

Just a small discrepancy I noticed while having to correct two links contained in the Enthalpy wiki article to the section of this page: Work_(thermodynamics)#Pressure–volume_work. The issue was that they linked to Work_(thermodynamics)#Pressure-volume_work (with a hyphen, not an en dash) instead of Work_(thermodynamics)#Pressure–volume_work (with an en dash, not a hyphen). In this article (Work_(thermodynamics)), there are 11 cases of "Pressure–volume work" with an en dash, and 2 cases of "Pressure-volume work" with a hyphen. I imagine that it is easy to make the mistake of not using an en dash when linking to Work_(thermodynamics)#Pressure–volume_work, like what happened in the Enthalpy article. Further, according to this article: https://www.grammarly.com/blog/en-dash/ , en dashes should only be used in complex compound adjectives, not regular compound adjectives. This article: https://www.dailywritingtips.com/en-dashes-clarify-compound-phrasal-adjectives/ seems to agree. And take a look at Bose–Einstein_condensate. It contains mostly en dashes, but some of the sources at the bottom also contain hyphens (use your browser's search function to search for – or -). https://english.stackexchange.com/questions/2116/when-should-i-use-an-em-dash-an-en-dash-and-a-hyphen seems to agree as well (feel free to check this source).

Now, in the case of "Pressure–volume work" or "Bose–Einstein condensate", the en dash is being used in place of an "and". According to wiki article Dash (as of March 30, 2019):

• The en dash but not the em dash indicates spans or differentiation, where it may be considered to replace "and" or "to" (but not "to" in the phrase "from … to …"):

  The French and Indian War (1754–1763) was fought in western Pennsylvania and along the present US–Canada border (Edwards, pp. 81–101).

Notice how it says [Not in citation given]. I wasn't able to access the source to check if the en dash can be used instead of "and".

Given the above, it seems as though that the hyphen should be used instead of the en dash. Unless there's better evidence to the contrary. --174.57.210.161 (talk) 04:35, 30 March 2019 (UTC)

Given that Wikipedia likes to distinguish between the en dash '–' and the hyphen '-', it seems to me appropriate to use the en dash when writing 'pressure–volume work'. I wouldn't be too happy to say that the use of the en dash here denotes exactly a meaning 'and'; I wouldn't like to say what exactly it means, but I think it is appropriate. Older texts, I guess, do not make the distinction.Chjoaygame (talk) 09:19, 30 March 2019 (UTC)

Chjoaygame, I agree that Wikipedia does like to distinguish between the en dash '–' and the hyphen '-'. Wikipedia:Manual_of_Style#Dashes isn't really helpful on this topic. Maybe you can find a better source. I agree that the en dash is fancy, but not necessarily the preferred style. It's not a span, as in the "US-Canada Border" example. I'm not sure what is meant by the article Dash that the en dash can indicate "differentiation". What's happening in "Pressure-Volume Work" and "Bose-Einstein Condensate" is that two nouns are being joined to form an adjective that describes something (i.e. 'Pressure-Volume' denotes the type of 'Work'). If I'm interpreting this correctly, these are Compound modifiers, and https://wiki.riteme.site/wiki/Wikipedia:Manual_of_Style#Hyphens says that a hyphen is used for this purpose on Wikipedia. It also says that the Michelson–Morley experiment, which should have an en dash, should redirect when containing a hyphen (Michelson-Morley experiment) However, Work_(thermodynamics)#Pressure–volume_work does not redirect when containing a hyphen (Work_(thermodynamics)#Pressure-volume_work). This needs to be fixed. I don't know how to make a re-direct for a heading in an article...

Anyway, whatever the choice that's made, this article needs to be consistent, and it would be nice if other science articles in Wikipedia could be cleaned up. 2601:88:8100:7443:4DBD:72A7:ABE2:723B (talk) 05:02, 23 April 2019 (UTC)

Hesitatingly accepting that Wikipedia likes to use the dash – to indicate a link between disparate concepts, I think the articles should write 'pressure–volume work', not 'pressure-volume work'. I feel the the hyphen links things essentially joined, for example 'a constant-pressure process'.Chjoaygame (talk) 06:13, 23 April 2019 (UTC)

Confusing title

This dispute at talk:Heat puts under question whether this article is named correctly. TL;DR: the present article restricts itself to reversible work. How do thermodynamics textbooks describe Joule’s paddles (a.k.a. “isochoric work”)? Incnis Mrsi (talk) 15:06, 28 July 2019 (UTC)

An isochoric process is generally not reversible; it is not an example of thermodynamic work. VQuakr (talk) 15:19, 28 July 2019 (UTC)

Really it’s reversibility of Joule’s work-to-heat converters which is discussed here? Again: such gurus as Planck, Born, or H.B. Callen certainly addressed Joule-style processes. They had to develop some terminology to distinguish them from work determinable with state variables. Incnis Mrsi (talk) 15:43, 28 July 2019 (UTC)

Th Joule's paddle is an example of mechanical work being converted to heat. It is irreversible. This gravitational work cannot be regarded as a thermodynamic work. It is called isochoric as it does not change the volume of water, and thus no thermodynamic work is done, only the internal energy of water changes.Lichinsol (talk) 15:41, 28 July 2019 (UTC)

The Joule-style processes -- which Incnis Mrsi is referring, as probably the processes in which energy conversions take place(like mechanical energy to heat, or electrical energy to heat)-- can be distinguishly calculated by proper experimentations. Factors such as gravity, tension,etc are the working variables in Joule's paddles, and the usual thermodynamic processes have their state variables.Lichinsol (talk) 16:06, 28 July 2019 (UTC)

according to whom?

A tag has been posted, asking "according to whom?", about the sentence "When it is done isochorically, and no matter is transferred, such an energy transfer is regarded as a heat transfer into the system of interest."

The currently used definition of heat transfer is that it is transfer of energy to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter.

The energy transfer in this case is supplied by externally applied work, defined as work in the surroundings, that does not act through immediate direct effect on the state variables of the system that define thermodynamic work for the system, for example volume, but, rather, acts on the system through friction. The energy transfer is not by transfer of matter.Chjoaygame (talk) 11:28, 29 July 2019 (UTC)

I want an answer to the following question: which authority describes non-equilibrium dissipative processes, a.k.a. Joule-style, as transfer of heat? Also, if the original formulation is ambiguous grammatically, then it would be good to search for a better grammar for replacement. Incnis Mrsi (talk) 12:34, 29 July 2019 (UTC)

Editor Incnis Mrsi asks "which authority describes non-equilibrium dissipative processes, a.k.a. Joule-style, as transfer of heat?" He is characterizing "Joule-style" processes as "non-equilibrium dissipative processes". He is also talking about "transfer of heat".

The text does not say "transfer of heat"; that is Editor Incnis Mrsi's locution. The text says "heat transfer"; that does not mean 'transfer of heat'. The text's locution is using the word 'heat' as an adjective to qualify the word 'transfer'. For comparison, if one says 'rapid transfer', people will not ask 'do you mean transfer of rapidity?'.

For the definition of transfer of energy as heat, the relevant question is not whether or not the transfer can be characterized as a non-equilibrium dissipative process. The relevant question is whether or not the transfer is by thermodynamic work or by transfer of matter.Chjoaygame (talk) 13:17, 29 July 2019 (UTC)

Wikipedia has an article heat transfer (which describes something different from Joule-style processes) where I understand the title as “transfer of heat”. Do we suffer from an unfortunate linguistic collision and this heat transfer is something different? Incnis Mrsi (talk) 13:24, 29 July 2019 (UTC)

The Wikipedia article Heat is specifically about heat in thermodynamics. The Wikipedia article Heat transfer is not primarily about heat in thermodynamics; it is about time rates or flows, topics that nearly exclude thermodynamics. One of the keys to thermodynamics is entropy, but that is not mentioned in the article Heat transfer. That Wikipedia uses a phrase as an article title does not commandeer that phrase so as to expropriate it from ordinary language usage in other articles. Chjoaygame (talk) 14:06, 29 July 2019 (UTC)

We discuss scientific terminology, not “ordinary language”. Again, is “heat transfer” as in Joule’s experiments a case of the thing discussed in the homonymous Wikipedia article? If it is, then an authoritative statement is necessary. If it is not, then we should work around the terminological collision. Incnis Mrsi (talk) 14:35, 29 July 2019 (UTC)

Wikipedia is primarily written in ordinary language, including scientific terminology as appropriate. The article entitled Heat transfer is not about the thermodynamic concept of transfer of energy as heat, the topic of the article Heat. The two articles are written from different frames of thought. The Heat transfer article is written largely from an engineering frame of thought. It happily talks about "thermal energy", a concept that is not large in the lexicon of thermodynamics. I think we do not need to concern ourselves about terminological collision.Chjoaygame (talk) 15:02, 29 July 2019 (UTC)

Indeed, where respectable authors told about “heat transfer”? We can read “energy transfer”, “transfer of energy”, etc. all the way, but is really the same vocabulary for production of heat by dissipative processes? Incnis Mrsi (talk) 15:21, 29 July 2019 (UTC)

For present-day thermodynamic thinking, the problem is in the idea of "production of heat". It suggests that heat is a substance, as distinct from a manner.Chjoaygame (talk) 17:07, 29 July 2019 (UTC)

Certainly I realize that the 1-form δQ is not exact (that is, Q cannot be understood as a function of state), and even not closed. A quantitative “substance” for Q is out of question, much like the hypothetical “total invariant mass” (for modern understanding, not a conserved quantity, and generally ill-defined). But this latter circumstance doesn’t preclude Chjoaygame from speaking about “transfer of matter”. Incnis Mrsi (talk) 20:54, 29 July 2019 (UTC)

There is no transfer of heat but the energy transferred from one system to another called as heat. This is what heat transfer signifies.Lichinsol (talk) 14:00, 29 July 2019 (UTC)

Would answer the main question of "according to whom?" asked by Incnis Mrsi as follows:

The definition of Heat in the respective wikipedia aricle has the answer. Any transfer of energy between 2 systems occur as heat. The Joule's paddle example is the same. If Incnis Mrsi understands the Joule's paddle process, he/she must have had understood the question's answer, and there would have been no need of this according to whom?. So, I would suugest him/her to go through it carefully.Lichinsol (talk) 14:29, 29 July 2019 (UTC)

Reversible work doesn’t produce heat. Joule’s things do. Incnis Mrsi (talk) 14:35, 29 July 2019 (UTC)

Any transfer of energy between 2 systems occur as heat. No, this is incorrect. Any non-work transfer of energy between two closed systems occurs as heat. VQuakr (talk) 14:56, 29 July 2019 (UTC)

Or much clearly,non-thermodynamic work, not including sorts like mechanical ones.Lichinsol (talk) 15:03, 29 July 2019 (UTC)

Joule's things are irreversible.

U must learn how reversible processes are made possible. This has nothing in context to anything in particular since we started.Lichinsol (talk) 14:53, 29 July 2019 (UTC)

---

If nobody objects, then I replace “… regarded as a heat transfer into…” with “… regarded as transformation to heat input for…”. Incnis Mrsi (talk) 14:58, 29 July 2019 (UTC)

I strongly object. The proposed words are repugnant to the thermodynamic conception and understanding of heat, and are not appropriate as a thermodynamic account of Joule heating.Chjoaygame (talk) 15:09, 29 July 2019 (UTC) The linked article Energy transformation uses the term "thermal energy" in a way that is not appropriate for an article written from a thermodynamic viewpoint.Chjoaygame (talk) 15:25, 29 July 2019 (UTC)

OK, let’s deem “thermal energy” a sort of red flag. Would simply “… regarded as heat input for…” be acceptable? Incnis Mrsi (talk) 15:30, 29 July 2019 (UTC)

The proposal is to replace "When it is done isochorically, and no matter is transferred, such an energy transfer is regarded as a heat transfer into the system of interest." with "When it is done isochorically, and no matter is transferred, such an energy transfer is regarded as a heat input into the system of interest." Such a replacement would confuse or mislead the reader. The word 'input' suggests that heat is something substantial, rather than a manner of transfer.Chjoaygame (talk) 16:57, 29 July 2019 (UTC)

Let’s try “the system of interest accepts such an energy transfer as a heat” then? Or, if anybody doesn’t like the verb to accept, then maybe “receives”? Incnis Mrsi (talk) 20:54, 29 July 2019 (UTC)

We seem to have a language problem here. We have seen mention of the Russian and the French Wikipedias. This is in the context also of the use here of the French phrase 'mal à propos'. The English word 'malaprop' is derived from the proper noun 'Malaprop', the surname of Mrs Malaprop, a character in a 1775 play, The Rivals, by Sheridan. She had a habit of misusing words. The Oxford English Dictionary records that 'malaprop' is used as noun, adjective, or verb. It seems to me that the heart of our present concern is a feeling that here the phrase 'heat transfer' is a misuse of words. Part of the cause of the worry is perhaps that there is a Wikipedia article entitled 'Heat transfer', which is about spread of energy in a way that is referred to as 'heat transfer'. This is not simplified by the present comment Any transfer between 2 systems occur as heat. This idea was repeated in the comment "Any non-work transfer of energy between two closed systems ..." The presently used definition of transfer of energy as heat is about transfer to or from one system. As I have mentioned, this wording takes into account that the surroundings are allowed any shenanigans they please, and are not required to be defined as a thermodynamic system.Chjoaygame (talk) 03:16, 30 July 2019 (UTC)

The penultimate phrase of the rant above, at last, brought something constructive. Where we have definition of transfer of energy as heat? In which Wikipedia article and which exactly definition? Incnis Mrsi (talk) 07:31, 30 July 2019 (UTC)

Also relevant here is that ordinary language is not compositional. That means that the meaning of a word is not fixed apart from its context. The meaning of the word 'heat' is context-dependent. It can be used in ordinary language and as a term of art in thermodynamics. It can be used as a verb, a noun, and an adjective.Chjoaygame (talk) 03:16, 30 July 2019 (UTC)

There is no problem with the previous phrase, it is correct. Rather the new one seems disturbing.Lichinsol (talk) 15:12, 29 July 2019 (UTC)

---

The question started as a simple one in the Heat page, which was whether transfer of matter is a thermodynamic work example, which has got far-fetched. If it is incorrect, then it should not have been stated in by placing it in conjunction with the word thermodynamic work in the first line of the article(Heat). Or though it might be correct, the phrase transfer of matter is ambiguous, it must be replaced with another suitable phrase .Lichinsol (talk) 15:34, 29 July 2019 (UTC)

I don't see "transfer of matter" as ambiguous. What alternative meanings are there? The phrases 'thermodynamic work' and 'transfer of matter' can well be placed in conjunction.Chjoaygame (talk) 17:15, 29 July 2019 (UTC)

“Amount of matter” (a.k.a. mass) is not (exactly) a conserved quantity, LoL – see above. Incnis Mrsi (talk) 20:54, 29 July 2019 (UTC)

The phrases 'thermodynamic work' and 'transfer of matter' can be placed in conjunction if they are different from each other. Placing them as they are implies that TRANSFER OF MATTER IS NOT A THERMODYNAMIC PROCESS. How is it so? And the 'Transfer Of Matter' Highness is nowhere used on the internet. It is much more equivalent to a Phase Transition. Lichinsol (talk) 04:46, 30 July 2019 (UTC)

As to "And the 'Transfer Of Matter' Highness is nowhere used on the internet. It is much more equivalent to a Phase Transition", please see the edit by Editor VQuakr: https://wiki.riteme.site/w/index.php?title=Heat&diff=next&oldid=908248715. As to the suggestion that 'transfer of matter' is equivalent to a 'phase transition', an ordinary speaker of English would not see such an equivalence in the sentence in question.

As to "The phrases 'thermodynamic work' and 'transfer of matter' can be placed in conjunction if they are different from each other. Placing them as they are implies that TRANSFER OF MATTER IS NOT A THERMODYNAMIC PROCESS. How is it so?" An ordinary speaker of English would not see such an implication in the conjunction in question.Chjoaygame (talk) 08:27, 30 July 2019 (UTC)

I need a proof(or reference) that transfer of matter cannot be a thermodynamic process. Rather Chjoyaygame's comment does not tell whether it is or not. It is wikipedia and nothing informally vague can be written in its articles. I am an ordinary English speaker.Lichinsol (talk) 09:28, 30 July 2019 (UTC)

In a context of thermodynamics, a transfer of matter is a commonly encountered kind of thermodynamic process, as implied by the above linked edit. I don't see how one could reasonably deny that it is a kind of thermodynamic process, in the context of thermodynamic conversation.Chjoaygame (talk) 10:02, 30 July 2019 (UTC)

That is what the point from where the debate started. If it is a thermodynamic process, then there is no meaning of writing it separately from the phrase thermodynamic work. Being a part of it, why is it separated? There is then no need of writing transfer of matter along with it ,especially not with the conjunction or. If an example has to be given, one should use such as, or like.

It definitely appears right now that both phrases are different and not related to each other.Lichinsol (talk) 10:16, 30 July 2019 (UTC)

There are three kinds of thermodynamic process: (1) thermodynamic work, (2) transfer of matter, (3) transfer of energy as heat.Chjoaygame (talk) 11:05, 30 July 2019 (UTC)

On what basis have you classified thermodynamic processes as above?Lichinsol (talk) 11:39, 30 July 2019 (UTC)

That classification is based on what textbooks say. First they distinguish processes that affect closed and open systems. An open system can experience transfer of matter. A closed system cannot. Then the textbooks consider the transfers of energy that closed systems can experience. There are two kinds, work and heat. Work is defined by changes in system state variables such as volume–pressure, and polarization – electric field. Heat is in the collected residual energy transfers. Then the textbooks proceed to consider open systems, for which there are transfers of matter along with energy.Chjoaygame (talk) 12:43, 30 July 2019 (UTC)

Thank you so much,Chjoaygame. I understood it completely now, and have no confusions. I apologize to have taken a major time from all the editors who participated in the discussion. It seems correct to cite transfer of matter with Mass transfer. Undo the change if inappropriate.Lichinsol (talk) 14:25, 30 July 2019 (UTC)

Thank you. I doubt that the link to that article is appropriate. That article is far wider in scope than the rather special concept of a transfer in thermodynamics, and might confuse the reader.Chjoaygame (talk) 15:02, 30 July 2019 (UTC)

Transport phenomena#Heat and mass transfer could be a better link target. VQuakr (talk) 15:25, 30 July 2019 (UTC).

Indeed, Mass transfer is wide in scope. Transport phenomena#Heat and mass transfer is better.Lichinsol (talk) 15:43, 30 July 2019 (UTC)

In this context, what you are doing is not called 'citing'. It is called 'Wikilinking'. 'Citing' is putting in a reference to a reliable source written like this , where 'xxx' denotes info about author, date, title, etc. Wikipedia articles are not reliable sources.Chjoaygame (talk) 16:40, 30 July 2019 (UTC)

Got it.Lichinsol (talk) 16:56, 30 July 2019 (UTC)

Still waiting for a reliable external source

Yes, as Chjoaygame says near the end of the above discussion, there is a difference on Wikipedia between Wikilinking and Citing a reliable source. Here, two plus years after the above discussion, no one has yet answered the question "According to whom" by providing a reliable source. Wikilinks help to explain words which may be unfamiliar to some readers, but Wikipedia policy is that non-obvious and especially controversial statements are supposed to be supported by reliable sources. Reading quickly, we seem to have several conflicting opinions in the above discussion. Can someone please provide a reliable external source for the claim in the intro that isochoric Joule heating without matter transfer is just heat transfer. One might argue that it is electrical work used to heat the system. Is there a textbook or review article that clearly says one or the other? Dirac66 (talk) 00:18, 10 October 2021 (UTC)

Fair comment, thank you Editor Dirac66.

I have some thoughts on this topic. I have seen a range of various treatments of it in textbooks, and at this moment I don't recall an ideal collection of reliable sources to uniquely settle the matter one way or another.

You write "One might argue that it is electrical work used to heat the system." That seems reasonable.

The present definition in Wikipedia is in terms of the mechanism of transfer.

To distinguish heat transfer from energy transfer accompanying matter transfer, Max Born says that the two must be by separate pathways. That is a definition in terms of mechanism of transfer. I think Born, along with Guggenheim, is the proper source for this. They are saying that energy transfer along with matter transfer in one and the same pathway cannot be uniquely split into heat transfer and energy transfer associated with matter transfer. Any such split has to be arbitrary, and so without thermodynamic safety.

I think it desirable to say that Joule's paddlewheel experiment demonstrates and measures the mechanical equivalent of heat. To me, that implies that in Joule's paddlewheel experiment, energy is supplied by the surroundings as work measured in the surroundings, which are not a thermodynamic system by Planck's definition. Planck holds that friction, due to activity in the surroundings, in a process, transfers energy as heat to the system. I would interpret Joule heating (due to friction as a current passes through the system) as energy transferred to the system as heat. The work is as measured in the surroundings. It is not P—V work; that is why it is called isochoric. In the system, under suitable conditions, in terms of thermodynamic state variables, it is measurable purely as S—T energy. I find it hard to to see that as thermodynamic work, and easy to see it as Joule did, as heat for the system.

Some people like to speak of "reversible work". They mean energy transferred and measured by change in the system's those thermodynamic state variables that can measure such transfers as P—V work, or polarisation work. I don't like that way of speaking because it comes too close to threatening the second law. But I am happy to call it thermodynamic work.Chjoaygame (talk) 02:12, 11 October 2021 (UTC)

Thermodynamic work is to be measured external to the system. It is to be measured as change in thermodynamic state variables measured outside the system. For example, for P—V work, the pressure in the system is to be measured by the pressure external to the system that is needed to keep a flexible wall stationary; the volume is also to be measured external to the system. The motions of pulleys, dynamos, and suchlike external to the system do not measure the thermodynamic variables of the system.

A pivotal point is that energy can change its form in a thermodynamic process. In a process, energy can leave the surroundings as work measured by a force × distance integral, and enter the system as heat. That was Joule's way.

When a system expands spontaneously against an external pressure, it does thermodynamic work precisely measured by a finite P—V difference of system variables; rate and system internal friction do not count. Some of that work enters the surroundings as heat because it occasions friction in the surroundings, or as kinetic energy of surrounding bodies. In a finite process, when the system is compressed by an external pressure, some of the work done by the surroundings enters the system as P—V work, and some of it enters the system as friction inside the system, registered as heat. Thereby, the second law is obeyed. It is a mathematical convenience to conduct fictive infinitely slow processes, but experimental processes have only finite durations, and non-zero time rates.

None of this commentary supplies the adequate bundle of reliable sources that Dirac66 rightly asks for, but I think it supplies criteria by which to assess the adequacy and reliability of relevant sources. There are many thermodynamic textbooks because none is perfect.Chjoaygame (talk) 10:47, 11 October 2021 (UTC)

Thanks for your explanations which I have been thinking about for a few days. I am dubious about your 3rd-last paragraph "A pivotal point ..." First, I consider heat and work to be forms of energy transfer rather than energy. Energy on the other hand can be thermal energy, mechanical kinetic or potential energy, electrical kinetic or potential energy, etc.

Also I have never heard of any single energy transfer being as described as work for the surroundings and heat for the system, or vice versa. I learned that a given energy transfer is either work for both system and surroundings, or heat for both. Do you have any referenced example of one and the same process being described as work for one and heat for the other?

Also I learned that the identification of work or heat depends on its effect on the surroundings, not the system. So Joule heating is described as work done by the surroundings on the system, because a voltage source in the surroundings supplies energy for an electric current to flow through the system. Then inside the system, the current interacts with the electrical resistance of the system to convert the electrical energy (not work) into thermal energy (not heat). So the overall result is that the thermal energy (temperature) is increased due to the energy transferred to the system as work, not as heat. Unfortunately I don't have a satisfactory reference either for this point. Dirac66 (talk) 02:06, 18 October 2021 (UTC)

Thank you for your further thoughts. I think they are all defensible. Textbooks are not particularly helpful here.

It is good that you frankly articulate that it is not easy to find textbooks bluntly describing a single energy transfer as work for the surroundings and as heat for the system.

I am impressed that Rumford thought that boring a cannon heated it, and that Joule thought that stirring a pot of water heated it, and that Joule heating occurs when an electric current passes through a body, and that Planck thought that rubbing its surface heated a body, a process that he called isochoric work. I am impressed that such transfers necessarily appear in the characteristically thermodynamic state variables of the body, namely temperature and entropy, and can be made to do so without appearing in externally directly measurable variables such as volume, pressure, electric field, which are defined without reference to thermodynamics.

I am not enamoured of the term 'thermal energy'.

I find no problem in thinking that in a process, work may be converted into heat. That means that I am comfortable with energy leaving the surroundings as work and entering the body as heat. I am comfortable saying that this is because there has been a change of form of energy. The only form of energy explicitly counted by state variables of a thermodynamic system is internal energy or its cohorts, enthalpy, Helmholtz free energy, and suchlike. These are specifically thermodynamic quantities, not forms of energy as often viewed, such as electrical, mechanical, chemical. I agree that people, such as yourself, and myself until I thought about it closely, often think of a transfer of energy as belonging to just one form, such as work or heat, common to the system and its surroundings. I am happy enough with your view that heat and work are kinds of transfer. But I don't see that logic requires them to be belong to mutually exclusive process mechanisms. I am impressed by the convolutions of thought that are required to say that energy leaving the surroundings as work must enter the body as work. I can't off the top of my head recall exactly where I have seen a textbook go through those convolutions leaving only a sense of confusion.

Some people like to talk about "reversible work". I think what they are talking about has some meaning, though I don't like their choice of words for it.

It is good that you explicitly articulate that "I learned that the identification of work or heat depends on its effect on the surroundings, not the system." I agree that measurements are preferably made through the surroundings. True, one can measure temperature by poking a thermometer into the body, and pressure by poking an anaeroid barometer into it. But mostly measurements are made in the surroundings. Work is measured in the surroundings, but thermodynamic work such as P–V work is also measured by state variables such as pressure and volume, that can be measured in the surroundings, though they describe properties of the system. When a system does P–V work on the surroundings, one has to admit that the second law would like to say that some of it arrives as friction or as kinetic energy, so that not all of it arrives as work or potential energy, such as when a vertical piston lifts a weight sitting on it. I like to think primarily that thermodynamic work is as Carnot saw it, work done by the system on its surroundings, when heat was converted into work, and that Joule measured the mechanical equivalent of heat. Joule didn't heat his pot of water by conduction and radiation. He heated it by friction. I think it fair to say that Planck thought that friction generates heat. It would be a pity to hide this.

Yes, again, "None of this commentary supplies the adequate bundle of reliable sources that Dirac66 rightly asks for, but I think it supplies criteria by which to assess the adequacy and reliability of relevant sources."Chjoaygame (talk) 19:07, 19 October 2021 (UTC)

Perhaps the following quote from Adkins (Equilibrium Thermodynamics, 3rd edition, 1983, Cambridge University Press, Cambridge UK) page 31 may partly help, though it is not an explicit statement such as Dirac66 rightly asks for.

However, it was not until Joule's work of the 1840s that the molecular motion theory was put on a sound basis by his demonstration of the direct quantitative equivalence of work and heat. In his experiments, he produced heating in various thermally isolated systems by performing work on them. He used many ways of doing the work: viscous dissipation in liquids, friction between solids, and, later, electrical heating. He compared the amounts of work required to produce a given amount of heat, using as his measure of heat the temperature rise which would be produced in unit mass of water.[1] He found that if the only effect of the work was to produce heating, then, in all cases, the amount of work and the corresponding amount of heat were in a fixed proportion to one another thus implying a direct equivalence of heat and work as forms of energy.

[1] Making the reference to water required a knowledge of the relative thermal capacities of the materials involved. These had been found earlier by Black using the method of mixtures (see page 34), which he was the first person to develop as a calorimetric technique.

Adkins does not say something such as 'amounts of work required to produce a given increase in internal energy'. He says "amounts of work required to produce a given amount of heat". We are inclined to think of heating as measured by $Q$, a quantity of heat. It is not a great stretch to think of a 'quantity of heat' as an 'amount of heat', though Wikipedia might call this 'synthesis'.Chjoaygame (talk) 19:23, 17 November 2021 (UTC)

I think it is probably best to quote the best sources we have found, even if they are not ideal in that they do not include the exact words we could wish for. Dirac66 (talk) 01:40, 18 November 2021 (UTC)

Thank you for that comment. Perhaps we may come up with something to corroborate or improve on Adkins.Chjoaygame (talk) 21:08, 18 November 2021 (UTC)

Planck, Max. Über die Begrűndung des zweiten Hauptsatzes der Thermodynamik, S.-B. Preuß. Akad. Wiss. phys. math. Kl., S. 453-463, 1926: "Auf Grund dieser Definition läßt sich das Prinzip der Unmöglichkeit des perpetuum mobile zweiter Art durch folgenden Satz ausdrücken, den ich für die einfachste und prägnanteste Fassung dieses Prinzips halte: »Die Wärmeerzeugung durch Reibung is irreversibel«. Damit ist zugleich, wei zu zeigen sein wird, der volle Inhalt des zweiten Wärmsatzes erschöpft."

I think this amounts to an authoritative statement that friction is a form of heat transfer. It may remind us of Count Rumford's thinking.

Perhaps an intellectual stumbling block might be a proposition that 'energy cannot be converted from one form to another in a transfer process'. I think that is not a real stumbling block. It seems reasonable to say that the energy leaves the machine in the surroundings as work and arrives in the thermodynamic system as heat. I think that energy can be transformed from one form to another in a transfer process. That would make immediate sense of the idea of the 'mechanical equivalent of heat'.Chjoaygame (talk) 14:22, 16 April 2023 (UTC)

Reason for undo of good faith edit

I have undone this good faith edit.

The edit has the merit of brevity. But it is so brief that a newcomer would get inadequate guidance to its meaning.Chjoaygame (talk) 00:17, 24 October 2020 (UTC)

work in general and thermodynamic work

Thermodynamic work can be distinguished from work done by agents or factors in the surroundings. For a closed system, the latter can be conceptually split into work that changes only the 'work-like' state variables of the system, for example P–V work, and what engineers call 'shaft work', used in Joule's paddle-wheel experiment, also called 'isochoric' work by some physicists. Such 'shaft work' or 'isochoric work' appears in the system's state variable increments as S–T energy.Chjoaygame (talk) 02:20, 6 December 2020 (UTC)

Perhaps if you give one example of general work that is not thermodynamic work; and one example of thermodynamic work that is not general work; readers might be able to engage with your assertions. Dolphin (t) 14:34, 6 December 2020 (UTC)

Thank you for your comment, Editor Dolphin.

Count Rumford bored metal for a cannon. His apparatus was doing shaft work in turning the drill. The turning of the drill was registered in the surroundings as mechanical work. The majority of the energy entered the metal block (the system) as heat generated by friction. (The frictional conversion of surrounding work into system heat was remarked upon also by Planck.) The metal block expanded a little as its temperature rose. Such expansion did work against the surrounding atmospheric pressure; such counts as thermodynamic work done by the metal block on the surroundings. Rumford observed that the metal block did not appreciably respond by spontaneously turning the drill. Friction is not reversible. Some of the metal block was removed from it as swarf by the drill. This was transfer of matter from the system to the surroundings; the energy transfer in such a mechanism does not resolve uniquely into work and heat energy transfers, and has to be counted simply as transfer of energy with matter.

Thermodynamic work always registers (at least in part) in the surroundings as work done by the system on the surroundings. Only little (or ideally no) thermodynamic work done by the system on the surroundings will be lost as friction in the pulleys that transfer it so as to lift a weight.

The experiments of Joule can be analysed likewise. They transferred energy as heat into the system through shaft work on the paddles and as I–V electrical work registered in the surroundings. The water of the system did not spontaneously turn the paddles, and the heated body did not spontaneously generate a current to drive the source of electrical work in the surroundings. The frictional transfer was irreversible.

Thermodynamics considers the 'system' as a relatively simple or even homogeneous body, as remarked by Planck:

§6. In the following we shall deal chiefly with homogeneous, isotropic bodies of any form, possessing throughout their substance the same temperature and density, and subject to a uniform pressure acting everywhere perpendicular to the surface.

Thermodynamics does importantly consider more complicated, though still carefully defined, 'systems', for example in the theory of Carathéodory, but the surroundings are permitted to contain mechanisms of unrestricted agency. For example, in the case of a steam engine, the 'working body' is some steam in a cylinder, while the surroundings include various pistons and levers, shafts, perhaps gears, and water tanks, as well as men shovelling coal into the firebox.Chjoaygame (talk) 15:55, 6 December 2020 (UTC)

Perhaps the following may help.

Thermodynamic work is work done by a thermodynamic system on its surroundings. The energy transferred from the working body or system to the surroundings must somehow be harnessed to lift a weight in the surroundings. The work required to lift a weight may be expressed in the form force × distance as, for example, $W_{\rm {weight}}=mg\,\Delta h$. Also the mechanism of the work must be precisely that by which the system will spontaneously transfer the energy if such is permitted by the second law of thermodynamics. A convenient example is P–V work, with the working body contained in a flexible bag surrounded by gas. An initial condition may be established at some pressure $P_{i}$, both in the surroundings and in the working body, at volume $V(P_{i})$. A thermodynamic operation may then initiate a thermodynamic process by reducing the pressure in the surroundings to $P_{f}$. Then the working body will spontaneously expand to volume $V(P_{f})$ to bring its pressure also to $P_{f}$, so that a new equilibrium is established. The thermodynamic work done in the process is $W_{\rm {thermo}}=\int _{P_{i}}^{P_{f}}V(P)\mathrm {d} P$. So far, this hasn't told us how the transferred energy will lift a weight. So far in this example, no mechanism has been described that will bring about $W_{\rm {thermo}}=W_{\rm {weight}}$. It would be different if instead of the surroundings being a gas, they were an incompressible liquid. But in a fundamentally different case, if the work is to be done through a paddle in the working body gas driving a shaft, not by P–V work, and the working body gas is contained in a rigid box, then the working body gas will not spontaneously drive the paddle, and will not be able to lift a weight; then the thermodynamic work will be zero, no matter how much we may wish otherwise.Chjoaygame (talk) 19:06, 8 December 2020 (UTC)

Unfortunately I don’t find either of your explanations helpful. Your original assertions are written using one set of words but each of your explanations is based on a mostly different set of words and concepts. If we make a statement based on half a dozen keywords, our explanation of the statement must focus on those half dozen keywords; we risk losing our audience if our explanation ignores some of the original keywords and substitutes new keywords.

It is unlikely that you will be able to persuade readers of the merit of your original assertion. I suggest you either leave it behind you and move on to something else; or begin thinking long and hard about how you might present an orderly, logical explanation that might persuade a knowledgeable but sceptical readership. Dolphin (t) 21:15, 8 December 2020 (UTC)

Short description

"Mode of..." is useless overhead to something that is meant to be terse. How about "Reversible energy transfer between a system and its surroundings"? VQuakr (talk) 21:21, 7 January 2021 (UTC)

The mechanism is essential to the definition of thermodynamic work;'mode' indicates that. 'Reversible' might suggest to a naïve reader that the second law can be by-passed.Chjoaygame (talk) 05:11, 8 January 2021 (UTC)

"Mode" doesn't indicate that. Why wouldn't we match the form of the first sentence? VQuakr (talk) 05:43, 8 January 2021 (UTC)

• Would 'kind of mechanism' be better than 'mode'?Chjoaygame (talk) 10:53, 8 January 2021 (UTC)

No. Nothing of the sort is necessary. It's just adding padding words to something meant to be terse. VQuakr (talk) 17:33, 12 January 2021 (UTC)

Noted.Chjoaygame (talk) 18:02, 12 January 2021 (UTC)

• The first sentence reads "In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings."

"Mode of" renders the first sentence's second half, "..., by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings.".Chjoaygame (talk) 18:02, 12 January 2021 (UTC)

Right, but the important part of the second half of the sentence if that it is reversible energy transfer, not that it is a mechanism. You are not conveying any information with "mode" or "mechanism". VQuakr (talk) 19:49, 12 January 2021 (UTC)

You propose that the second half of the sentence is about reversibility, but the words don't say that. The mechanism is the important thing. When a thermodynamic system spontaneously transfers some energy to the surroundings by doing thermodynamic work, the surroundings cannot return all of that energy to the system as thermodynamic work: in a process of return, some of it will go back into the system as heat, because of friction. The second law says so. The transfer was not reversible.Chjoaygame (talk) 21:23, 12 January 2021 (UTC)

Yes, obviously in any real system energy will be lost to the surroundings as heat. Isentropic transfer is the limit when dealing with work, not what is practically attainable. 2nd law doesn't say what you seem to think it does, though. And even still, you are stuck on a word that doesn't convey what you are trying to say. Like, at all. Meanwhile, reversibility has a well-defined and broadly recognized meaning in thermodynamics. VQuakr (talk) 22:01, 12 January 2021 (UTC)

'Reversible' is a technical term, an abbreviation in context; it isn't literally right. It might suggest, to a person who consults the article because he/she doesn't know what thermodynamic work is, that the second law can be by-passed.Chjoaygame (talk) 22:35, 12 January 2021 (UTC)

No short description is a complete discussion of the topic. It is by its nature terse. Again, 2nd law doesn't preclude truly reversible processes, which do actually occur on a micro scale - "reversible" is fully accurate. 2nd law precludes the entropy of a closed system from decreasing, but does not prevent it from remaining constant. Where at WP:SHORTDES does it say we shouldn't use technical terms? VQuakr (talk) 23:40, 12 January 2021 (UTC)

Quoting: "No short description is a complete discussion of the topic."

Agreed.Chjoaygame (talk) 01:20, 13 January 2021 (UTC)

Quoting: It is by its nature terse.

It should be brief, within the bounds of accuracy and comprehensibility.Chjoaygame (talk) 01:20, 13 January 2021 (UTC)

Quoting: Again, 2nd law doesn't preclude truly reversible processes, which do actually occur on a micro scale - "reversible" is fully accurate.

With respect, "reversible" isn't fully accurate. The second law is a macroscopic statement. Its scope doesn't extend to a micro scale. Thermodynamic work is a macroscopic concept. The micro scale is not directly relevant here.Chjoaygame (talk) 01:20, 13 January 2021 (UTC)

Quoting: 2nd law precludes the entropy of a closed system from decreasing, but does not prevent it from remaining constant.

(Just a small point. We usually here use the term 'isolated' for a thermodynamic system that is constrained so as to have no transfers in or out. I would like to follow that usage.)

An isolated thermodynamic system, starting in a state of internal thermodynamic equilibrium, and not subject to a thermodynamic operation, undergoes no thermodynamic process, there is no transfer, and its entropy remains constant in time. The short statement doesn't refer to that case; it is explicitly about transfer of energy as work. The law is about thermodynamic processes. An isolated thermodynamic system that has internal partitions, starting in a state of thermodynamic equilibrium as constrained by those partitions, can undergo a thermodynamic process when the permeabilities of the partitions are changed by a thermodynamic operation. The second law says that if such a thermodynamic process occurs, so that a new thermodynamic equilibrium is brought about, then the sum of the entropies of the compartments increases.Chjoaygame (talk) 01:20, 13 January 2021 (UTC)

Quoting: Where at WP:SHORTDES does it say we shouldn't use technical terms?

Our concern here is to send the right message to the reader. If technical terms will send the right message to the reader, it is perhaps ok for us to use them. 'Reversible' is a technical term that might suggest, to a person who consults the article because he/she doesn't know what thermodynamic work is, that the second law can be by-passed. That would not be a right message.Chjoaygame (talk) 01:20, 13 January 2021 (UTC)

Yes, the example you give of gas permeation is an irreversible process. You still seem to be missing that the 2nd law precludes a decrease in entropy; it does not say that the net entropy must increase. If the reader relies only on short descriptions, they will have an incomplete understanding of all topics. Not a problem we need to try to avoid, nor one that is addressed, at all, by your proposed change. VQuakr (talk) 01:27, 13 January 2021 (UTC)

The article is about transfer of energy as work, not about the case of no transfer. Nor is it limited to theoretical, but never actual, limiting cases, to which using the word 'reversible' would limit the short description, making it misleading.Chjoaygame (talk) 01:59, 13 January 2021 (UTC)

You brought up the irrelevant example, not me. A limit is a limit, whether you can build a machine that achieves it or not. This is a physics article, it makes sense to use physics terms in the way they are understood in a physics context. To do so is the opposite of misleading. VQuakr (talk) 02:27, 13 January 2021 (UTC)

You seem determined to stipulate 'reversible' limiting processes. They include 'reversible' heat transfer. So you would obliterate the difference between heat and work transfers. The decisive factor is mechanism, which you seem determined to hide.Chjoaygame (talk) 02:43, 13 January 2021 (UTC)

Um, no. Heat flow is not reversible; an increase in entropy always accompanies. I am "determined" to include it because reversibility is a defining characteristic of work. "The decisive factor is mechanism" is a meaningless phrase. Literally, it doesn't mean anything in English. VQuakr (talk) 04:28, 13 January 2021 (UTC)

Carnot cycle.Chjoaygame (talk) 04:42, 13 January 2021 (UTC)

A short title is just a method of cataloging subjects, it does not have to, nor can it possibly, define terms with any kind of detail. This hackling is just more of the same shortsightedness that doesn't see the forest for the trees. kbrose (talk) 14:39, 13 January 2021 (UTC)

Always glad of your help. Happy with 'form' to replace 'mode'. Work is a form of energy transfer.Chjoaygame (talk) 16:06, 13 January 2021 (UTC)

I now see that my edit has been undone by Editor kbrose, with the cover note 'no improvement', but no justification on this page, though the entry has been debated here: his cover note is not adequate. It comes on top of his ill-mannered comment "This hackling is just more of the same shortsightedness that doesn't see the forest for the trees." This adds up to high-handedness.Chjoaygame (talk) 03:32, 14 January 2021 (UTC)

Whether the response was high-handed or not, your proposed edit indeed wasn't an improvement, and you didn't get consensus for it. VQuakr (talk) 19:36, 20 January 2021 (UTC)

'distinct' versus 'distinguished'

I thank you for your interest. Nevertheless, I think 'distinguished' is the right word for the job. 'Distinct' doesn't have the same depth of meaning. The point is more than distinctness; it is special distinctness. An example of the difference is in group theory. The identity element (0 for additive groups) is more than just distinct. Every group element is distinct. But 0 is special, and it is customary to express this by saying that it is distinguished. I think this custom is suitable here. For example, isobaric processes constitute a distinct class of processes, but I think they are not distinguished in quite the same way as are work, heat, and matter transfer, which are distinguished in the notation for changes of internal energy.

I agree that 'measureable' is better.

I thought about 'these' and 'those', and preferred 'those'.Chjoaygame (talk) 21:23, 13 April 2023 (UTC)

@Dirac66: Hi, Dirac66. I would be glad of a reply to the above.Chjoaygame (talk) 08:22, 15 April 2023 (UTC)

I think 'distinguished' as an adjective is used more to describe people. For example, J.W. Gibbs was a distinguished scientist. However if you like the word, we could use it as a verb in the phrase 'can be distinguished'. Perhaps something like:

In thermodynamics, work is one of three classes of thermodynamic process which can be distinguished, in which a thermodynamic system can interact with its surroundings in energy transfer. Thermodynamic work occurs by a mechanism through which the system can spontaneously exert externally measurable macroscopic forces on its surroundings. In the surroundings, such mechanical work can be made to lift a weight.

The last "distinct" could just be deleted: "The remaining two classes of thermodynamic process are heat and transfer of matter."

And as for "these" and "those", I prefer "these" because it means "the ones we have just mentioned", which is the case here. Dirac66 (talk) 16:19, 15 April 2023 (UTC)

It's not distinctness as contrasted with blurriness that is the point. It's primacy. How about

In thermodynamics, work is one of the three prime classes of thermodynamic process by which a thermodynamic system can interact with its surroundings in energy transfer. Thermodynamic work occurs by a mechanism through which the system can spontaneously exert externally measurable macroscopic forces on its surroundings. In the surroundings, such mechanical work can be made to lift a weight. The remaining two prime classes of thermodynamic process are heat and transfer of matter.

? Chjoaygame (talk) 00:02, 17 April 2023 (UTC)

Sorry but I do not understand what is meant by "primacy" and "prime classes" in this context. Dirac66 (talk) 01:37, 17 April 2023 (UTC)

'Prime' means something like 'important'. So does 'distinguished'. But 'important' doesn't quite do it for me.

How about 'principal'?

The change in internal energy is often written in some way such as

$\Delta U=T\Delta S-P\Delta V+\mu \Delta N$.

I see the three terms as exemplifying the three principal (= prime = distinguished) classes of process.Chjoaygame (talk) 05:36, 17 April 2023 (UTC)

'Principal' is clearer, although some readers might wonder if there are also 'secondary' classes. An even clearer word might be 'fundamental'. Dirac66 (talk) 12:29, 17 April 2023 (UTC)

Ok, 'fundamental' is ok, but I wonder if it is going too deep or too far? Well, there are secondary classes. Such as radiation, conduction, and friction for heat, and electric field, magnetic field, and pressure, for work.Chjoaygame (talk) 13:32, 17 April 2023 (UTC)

Yes, 'fundamental' is probably too strong. Let's go with 'principal' which seems most accurate. However what you have called 'secondary classes' I would describe as 'subclasses': radiation, conduction and friction are subclasses of heat; and work done by (or against) electric fields, magnetic fields and pressure are subclasses of work. Dirac66 (talk) 14:43, 17 April 2023 (UTC)

Ok, let's go with 'principal'. We don't need to go into the 'subclass'/'secondary class' thing?Chjoaygame (talk) 15:14, 17 April 2023 (UTC)

Done. And I agree to omit subclass/secondary. There are lots of examples later.

And one more related question: do you think the other two principal classes should be named at the end of the first sentence (as in today's edit by Slaythe), or at the end of the first paragraph (as they were previously and still are)? I could accept either, but clearly not both (as now) which is unnecessary repetition. Dirac66 (talk) 21:14, 17 April 2023 (UTC)