For a redox reaction that is non-spontaneous, which of the following is true under standard conditions?

• A. E° > 0
• B. ΔG° < 0
• C. K > 1
• D. E° < 0; ΔG° > 0; K < 1

Answer: (D)

The key idea is how standard electrochemical parameters reflect spontaneity. For a redox reaction under standard conditions, the sign of the standard cell potential tells you whether the written direction is spontaneous: a positive E°cell means the reaction tends to proceed on its own, while a negative E°cell means it does not and would go in reverse.

If the reaction is non-spontaneous in the written direction, E°cell must be negative. That directly ties to Gibbs energy through ΔG° = −nF E°cell: with E°cell negative, ΔG° becomes positive, meaning the process requires energy input and is not spontaneous under standard conditions.

Relating to the equilibrium constant, ΔG° = −RT ln K, a positive ΔG° implies ln K is negative, so K < 1. That indicates the equilibrium lies toward the reactants, consistent with non-spontaneity in the forward direction.

In short, non-spontaneous in standard conditions corresponds to E° < 0, ΔG° > 0, and K < 1.