Question

Given the equation ΔG = ΔH - TΔS, which set of conditions would result in a reaction that is unambiguously nonspontaneous?

1) entropy decreases and the reaction is endothermic
2) entropy increases and the reaction is exothermic
3) entropy stays the same and there is no change in enthalpy
4) entropy decreases and the reaction is exothermic
5) entropy increases and the reaction is endothermic

Answer 1

The set of conditions that would result in a reaction being unambiguously nonspontaneous is when entropy decreases and the reaction is endothermic, which corresponds to ∆G = ∆H - T∆S where ∆H is positive and ∆S is negative.

Step-by-step explanation:

To determine the conditions under which a reaction is unambiguously nonspontaneous, we can refer to the equation ∆G = ∆H - T∆S. A reaction is nonspontaneous when the Gibbs free energy change (∆G) is positive. According to the second law of thermodynamics, for a process to be spontaneous, the change in entropy of the universe (∆Suniv) must be greater than 0. If ∆Suniv is less than 0, the process is nonspontaneous. Therefore, a reaction that is endothermic (∆H positive) and is accompanied by a decrease in entropy (∆S negative) would result in a positive ∆G, making it nonspontaneous under all conditions. Among the given options, this corresponds to:

1. entropy decreases and the reaction is endothermic