Which statement describes a spontaneous reaction at standard state?

Which statement describes a spontaneous reaction at standard state?

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

Answer: (D)

Spontaneity at standard state is shown by a negative standard Gibbs free energy change. When ΔG° is negative, the reaction favors the formation of products under standard conditions, and the equilibrium constant must be greater than 1. This comes from the relationship ΔG° = -RT ln K, where RT is positive; a negative ΔG° makes ln K positive, so K > 1. So the statement with ΔG° < 0 and K > 1 best describes a spontaneous reaction at standard state. The other combinations clash with the equation linking ΔG° and K, so they don’t describe spontaneity under standard conditions.

Spontaneity at standard state is shown by a negative standard Gibbs free energy change. When ΔG° is negative, the reaction favors the formation of products under standard conditions, and the equilibrium constant must be greater than 1. This comes from the relationship ΔG° = -RT ln K, where RT is positive; a negative ΔG° makes ln K positive, so K > 1. So the statement with ΔG° < 0 and K > 1 best describes a spontaneous reaction at standard state. The other combinations clash with the equation linking ΔG° and K, so they don’t describe spontaneity under standard conditions.