SAGAR SINGH - IIT DELHI
Last Activity: 14 Years ago
Dear student,

where, for a generalized equation of the form:

The capital letters A, B, M and N in equation represent respectively the reactants and products of a given reaction while the small letters represent the coefficients required to balance the reaction.

At equilibrium, DG = 0 and Qreaction corresponds to the equilibrium constant (Keq) described earlier.
In the case of an electrochemical reaction, substitution of the relationships DG = -nFE and D
G
0 = -nFE0 into the expression of a reaction free energy and division of both sides by -nF gives the Nernst equation for an electrode reaction:

Combining constants at 25oC (298.15 K) gives the simpler form of the Nernst equation for an electrode reaction at this standard temperature:

In this equation, the electrode potential (E) would be the actual potential difference across a cell containing this electrode as a half-cell and a standard hydrogen electrode as the other half-cell. Alternatively, the relationship in equation can be used to combine two Nernst equations corresponding to two half-cell reactions into the Nernst equation for a cell reaction:
