Redox Potential (Eh)

The redox potential, Eh, is the energy gained by transferring 1 mole of electrons from an oxidant to H₂. It is measured in volts relative to a hydrogen electrode which is at zero. Eh can be calculated from the Nernst equation:

Eh = E^o – RT/nF ln [products]/[reactants]

Where:
E^o is the standard potential of the redox reaction in volts;
R is the gas constant (8.3 x 10^-3) kJ K^-1;
T is the temperature measured in Kelvins (K);
F is Faraday’s Constant (96.5 kJ V^-1);
n is the number of electrons in half reaction; and
[ ] is the activity of products and reactants.

It is negative in a reducing medium and positive in an oxidizing medium. EH and pE are related by the following:

pE = nF/2.303RT * Eh