What is the spontaneity criterion for a galvanic cell based on E°cell?

• A. If E°cell > 0, the reaction is spontaneous as written.
• B. If E°cell > 0, the reaction is the opposite of spontaneous.
• C. If E°cell = 0, the reaction is spontaneous.
• D. E°cell has no bearing on spontaneity.

Answer: (A)

The key idea is that the sign of the standard cell potential tells you whether a redox reaction will occur on its own in a galvanic cell. A positive E°cell means the Gibbs free energy change under standard conditions is negative: ΔG° = −nF E°cell. With E°cell > 0, ΔG° < 0, so the process is thermodynamically favorable and proceeds spontaneously in the direction written, with electrons flowing from the anode to the cathode. If E°cell were negative, the forward reaction wouldn’t be spontaneous and would run in reverse; if E°cell were zero, the system would be at equilibrium with no net reaction. So a positive E°cell indicates spontaneity in the written direction.