Temperature at which a reaction becomes spontaneous
A reaction has ΔH = +50 kJ/mol and ΔS = +125 J/mol·K. Above what temperature is it spontaneous?
Answer C: explanation for every choice
A
This divides 50 by 125 without converting kJ to J.
B
This treats the entropy value as a temperature.
C
Correct. ΔG = 0 when T = ΔH/ΔS = 50,000/125 = 400 K. Above that, TΔS exceeds ΔH.
D
This multiplies ΔH by ΔS.
TakeawayThe crossover temperature is T = ΔH/ΔS (matching units).
Equation usedGibbs free energy
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