From this example it appears that cell voltages are additive, as are free energies. Just as we can write for free energies of a reaction, 24.1 kcal + 26.6 kcal = 50.7 kcal, we can write for cell voltages, 0.52 volt + 0.58 volt = 1.10 volts.

This case is especially simple because the number of electrons transferred is the same for all reactions, n = 2. But remember that cell potential or voltage does not represent a quantity of energy.

It is a tendency to react, or an electron "pressure." The quantity of energy, which by the principles of thermodynamics always is additive when reactions are added, is the free energy, D G = -nFE. Whenever there is the slightest question as to whether voltages are additive in a given situation, go back and work with free energies instead.