Upon completion of this topic, learners will be able to:

• calculate the cell potential for non-standard conditions.

What is the effect of change in the concentration of reactants on cell potential?

A change in concentration affects the change of cell potential which is a result of free energy change. According to chemical thermodynamics:

∆G = ∆G^o + RT ln Q

Where, Q is the reaction quotient, and Q is used to calculate the effect of concentration on DG. Since DG = – nFEcell and ∆G^o = – nFE^o_cell, the equation becomes

– nFE_cell = – nFE^o_cell + RT ln Q

Dividing each side of the equation by – nF gives

This equation gives the relationship between the cell potential and the concentrations of the cell components and is called the Nernst equation.

At 25°C:

During the operation of a Galvanic cell, electrons flow from the anode to the cathode, resulting in product formation and a decrease in reactant concentration. Thus Q increases, which means that E_cell decreases. Eventually, the cell reaction reaches equilibrium. At equilibrium, there is no net transfer of electrons, so E_cell = 0 and Q = K, where K is the equilibrium constant.