D41.2 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 ΔrG is related to ΔrG° by the reaction quotient, Q, and a similar relationship can be applied to cell potentials:

ΔrG = ΔrG° + RT lnQ
nFEcell = nFE°cell + RTlnQ

Rearranging the variables gives the Nernst equation:

 E_{\text{cell}} = E_{\text{cell}}^{\circ}\;-\;\dfrac{RT}{nF}\;\text{ln}\;Q

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.

Activity: Is a Redox Reaction Spontaneous?

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