Standard electrode potential (data page)

The data below tabulates standard electrode potentials (E°), in volts relative to the standard hydrogen electrode, at: The Nernst equation adjusts for general concentrations, pressures, or temperatures.
 * Temperature 298.15 K;
 * Effective concentration 1 mol/L for each aqueous or amalgamated (mercury-alloyed) species;
 * Unit activity for each solvent and pure solid or liquid species; and
 * Absolute partial pressure 101.325 kPa for each gaseous reagent &mdash; the convention in most literature data but not the current standard state (100 kPa).

Simultaneous half-reactions do not in general add voltages, but instead add Gibbs free energy change: the product of the voltage and the number of electrons transferred, typically the Faraday constant. For example, from Fe + 2 Fe(s)  (–0.44 V), the energy to create one neutral atom of Fe(s) from one Fe ion and two electrons is 2 × 0.44 eV = 0.88 eV, or 84 895 J/(mol ). That value is also the standard formation energy for an Fe ion, since and Fe(s) both have zero formation energy.

Data from different sources may cause table inconsistencies. For example:  Additivity of Gibbs energy implies $$E_3=\frac{2\cdot E_2-1\cdot E_1}{1}=0.154\text{ V,}$$ not the experimental 0.159 V.

Table of standard electrode potentials
Legend: (s) – solid; (l) – liquid; (g) – gas; (aq) – aqueous (default for all charged species); (Hg) – amalgam; bold – water electrolysis equations.