Electrochemistry

The study of chemical reactivity in which the focus is on the

electronic structure of the atoms and molecules involved.

The elements involved in an electrochemical reaction are

characterized by the number of electrons associated with

each atom of the element. This number of electrons is often

expressed in terms relative to the number of electrons such an

atom would have when electrically neutral. The term used

for such an expression is the oxidation state of the atom.

For example, oxygen has 6 positively charged protons, and

thus in the neutral state would also have 6 (negatively charged)

electrons. In dihydrogen monoxide (ie, water), each oxygen

atom can be viewed as surrendering two electrons, one to each

of two hydrogen atoms. The oxidation state of each oxygen

atom in water then is -2, and of each hydrogen atom in water is

+1.

In the nomeclature of chemistry, the substance losing electrons is said to

be the reductant and is oxidized' by the the other substance(s) in

the reaction which gain the electrons.

The substance gaining the electrons is said to be the oxidant and is

said to be reduced (by the reductant).

Though historically oxidation, as the name suggests, many reactions not

directly involving oxygen, but involving changes of oxidation states,

(redox reactions) are possible.

In fact, even fire can be fed by an oxidant other than oxygen:

Fluorine fires are often unquenchable, as fluorine is an even stronger oxidant

(it has a higher electronegativity) than oxygen.

This is a simple example, because oxygen and hydrogen have few

oxidation states at the temperatures and pressures commonly found on Earth.

However, many of the transition metal elements each have a rich variety

of commonly occuring oxidation states.

A spontaneous electrochemical reaction can be used to generate an

electrical current. This is the basis of all batteries or

fuel cells. For example, gaseous oxygen (O₂) and

hydrogen (H₂) can be combined in a fuel cell to form water and

energy (a combination of heat and current, typically).

The reverse case, for non-spontaneous electrochemical reactions, can be driven forward by the application of a current at sufficient voltage. The

electrolysis of water into gaseous oxygen and hydrogen is

the appropriate example of this.

/Talk