For a reaction to be spontaneous under standard conditions at all temperatures, the signs of ΔH° and ΔS° must be __________ and __________, respectively.

Question

Quizplus · Accepted Answer

A spontaneous reaction is one in which the Gibbs free energy change (ΔG) is negative. Using the equation ΔG° = ΔH° - TΔS°, we can see that for ΔG° to be negative at all temperatures, either ΔH° must be negative or TΔS° must be positive. Thus, the signs of ΔH° and ΔS° must be opposite (i.e. ΔH° is negative and ΔS° is positive) for the reaction to be spontaneous at all temperatures. Therefore, the answer is choice C (-, +).

For a Reaction to Be Spontaneous Under Standard Conditions at All