[ket]

Hi! I'm a 11th grade homeschooled student. I'm currently learning chemistry on my own and came across this question while I was practicing:

A particular reaction is spontaneous up to 475 K and becomes non-spontaneous at temperatures above 475 K. Is this reaction exothermic or endothermic? Does entropy increase or decrease during this reaction?

From what I understand, the enthalpy change will be negative and entropy change will also be negative. Hence, the reaction is exothermic.
The person correcting my questions said it's wrong. I would really appreciate it if someone can help me answer this. Thank you!

[mjc123]

You are correct. From ΔG = ΔH - TΔS, in order for ΔG to become more positive with increasing temperature, ΔS must be negative. Then ΔH must be negative for ΔG to be negative at lower temperatures.

[ket]

You are correct. From ΔG = ΔH - TΔS, in order for ΔG to become more positive with increasing temperature, ΔS must be negative. Then ΔH must be negative for ΔG to be negative at lower temperatures.

Thank you so much!