If a redox reaction is non-spontaneous, what can be said about K?

• A. K > 1
• B. K = 1
• C. K < 1
• D. Cannot determine

Answer: (C)

Spontaneity of a reaction is linked to Gibbs free energy and to the equilibrium constant. If a redox reaction is non-spontaneous under standard conditions, its standard Gibbs energy change ΔG° is positive. The relationship ΔG° = -RT ln K connects this to the equilibrium constant K. With ΔG° > 0, the natural log term must be negative, so ln K < 0 and thus K < 1. This means the reactants are favored at equilibrium, aligning with the non-spontaneous nature of the process. Remember, if K > 1, products would be favored and the reaction would be spontaneous; if K = 1, the system sits at equilibrium with neither side preferred.