How is the cell voltage calculated from two half-reaction potentials?

To calculate the cell voltage (or standard cell potential, $E^{\circ }$) of an electrochemical cell, you must break the overall oxidation-reduction reaction into two separate half-reactions: one for oxidation and one for reduction.12

The calculation process involves the following steps:

• Identify Half-Reactions: Determine the reduction potential ($E^{\circ }$) for each half-reaction from a standard table.1
• Reverse the Oxidation Half-Reaction: Since standard tables typically list reduction potentials, you must reverse the direction of the oxidation half-reaction to match the actual process occurring in the cell. When you reverse a half-reaction, you must also reverse the sign of its potential (e.g., a negative value becomes positive).1
• Sum the Potentials: Add the reduction potential of the reduction half-reaction to the (now reversed) potential of the oxidation half-reaction. The resulting sum is the standard cell potential.1

A positive $E^{\circ }$ value indicates that the net reaction is expected to occur spontaneously under standard conditions.1