Standard electrode potential (data page)
The data below tabulates standard electrode potentials, in volts relative to the standard hydrogen electrode, at:
- Temperature ;
- Effective concentration 1 mol/L for each aqueous or amalgamated species;
- Unit activity for each solvent and pure solid or liquid species; and
- Absolute partial pressure for each gaseous reagent — the convention in most literature data but not the current standard state.
Electrode potentials of successive elementary half-reactions cannot be directly added. However, the corresponding Gibbs free energy changes can be added. Those free energy changes satisfy
where electrons are transferred, and the Faraday constant is the conversion factor describing Coulombs transferred per mole electrons. For example, from
the energy to form one neutral atom of Fe from one Fe ion and two electrons is or 84 907 J/. That value is also the standard formation energy for an Fe ion, since and Fe both have zero formation energy.
Data from different sources may cause table inconsistencies. For example: From additivity of Gibbs energies and canceling common factors, one must have But that equation does not hold exactly with the cited values.