D41.4 Nernst Equation

Now that the connection has been made between standard Gibbs free energy change and standard cell potentials, we can consider the situation under nonstandard conditions. Recall that Δ_rG is related to Δ_rG° by the reaction quotient, Q. A similar relationship can be applied to cell potentials:

Rearranging the variables gives the Nernst equation:

The Nernst equation can be used to calculate the cell potential at concentrations or partial pressures that differ from standard conditions, which is often the case for voltaic cells.