QuestionThermodynamics / spontaneity
Which one of the following changes will necessarily lead to a non-spontaneous change?
- (a) Positive ∆H and positive ∆S
- (b) Negative ∆H and negative ∆S
- (c) Positive ∆H and negative ∆S
- (d) Negative ∆H and positive ∆S
Answer: (c) Positive ∆H and negative ∆S
ΔG = ΔH − TΔS. ΔH > 0 and ΔS < 0 → ΔG > 0 at all temperatures → never spontaneous → (c). (a) spontaneous at high T; (b) at low T; (d) always spontaneous.