the electrode potential of an electrolytic system at equilibrium. At constant temperature, the oxidation-reduction potential is only dependent on the composition of the medium and is equal to the potential difference between a neutral electrode and a solution containing interconvertible, oxidized and reduced forms of a compound.

The simplest illustration of oxidation-reduction potential involves ferric oxide and ferrous oxide ions: Fe³⁺ ions capture electrons from the metal and convert into Fe²⁺ ions, which, in turn, are able to effect the reverse reaction; the potential at which the forward and reverse reactions kinetically balance each other is the oxidation-reduction potential. An increase in the oxidizing strength of the medium is accompanied by an increase in the oxidation-reduction potential. The values that are derived for oxidation-reduction potentials are used to solve various problems in electrochemistry, biochemistry, and analytical chemistry. These values, like the values for standard potential that are obtained from a hydrogen electrode, proceed from an arbitrary zero point.