How do you calculate standard emf from the difference of electrode potentials?

To calculate the standard electromotive force (emf) of a galvanic or voltaic cell from the difference of electrode potentials, one needs to consider which electrode is serving as the anode and which as the cathode. The standard reduction potential values are typically tabulated for reduction reactions, meaning that they give the voltage associated with gaining electrons.

The correct formula involves subtracting the standard reduction potential of the anode (the negative electrode where oxidation occurs) from that of the cathode (the positive electrode where reduction takes place). This results in the total voltage for the cell's operation.

In this context, if you denote the standard reduction potential of the cathode as E°(right) and that of the anode as E°(left), the overall cell potential is given by the difference:

E° = E°(cathode) - E°(anode).

Here, if the anode is on the left and the cathode is on the right, this simplifies to E° = E°(right) - E°(left), which matches the formula in the selected answer.

This method underscores the importance of recognizing the roles of the electrodes in determining the direction of electron flow, which is central to