If E°cell > 0, what can be said about the equilibrium constant K?

• A. K > 1
• B. K = 1
• C. K < 1
• D. K cannot be determined

Answer: (A)

A positive standard cell potential means the reaction is spontaneous under standard conditions, which corresponds to a negative standard Gibbs energy change, ΔG°. Since ΔG° = -nF E°cell, a positive E°cell makes ΔG° negative. The thermodynamic link ΔG° = -RT ln K then gives ln K = nF E°cell / RT. With E°cell > 0, ln K is positive, so K > 1. That is, the equilibrium lies toward products. If E°cell were zero, K would be 1; if E°cell were negative, K would be less than 1.