Cell potential and Gibbs free energy

[juchung7]

When are you supposed to convert gibbs free energy into cell potential (deltaG=-nFE) instead of just subtracting standard cell potentials?

[Rachel Brown 3A]

You do this when you are trying to get the cell potential of a half reaction or you are given cell potentials of half reactions. For some reason, half reaction cell potentials are not state functions so you cannot just add or subtract them.