Chemistry · Thermodynamics & Thermochemistry

JEE Main 2025 — 24 January, Morning Shift — Question 32

Let us consider an endothermic reaction which is non-spontaneous at the freezing point of water. However, the reaction is spontaneous at boiling point of water. Choose the correct option.

Option A:
Both $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ are ( +ve )
Correct
Option B:
$\Delta \mathrm{H}$ is $(-\mathrm{ve})$ but $\Delta \mathrm{S}$ is $(+\mathrm{ve})$
Option C:
$\Delta \mathrm{H}$ is $(+\mathrm{ve})$ but $\Delta \mathrm{S}$ is $(-\mathrm{ve})$
Option D:
Both $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ are (-ve)

Answer: A

Step-by-step solution

Reaction is spontaneous at relatively high temperature and non-spontaneous at low temperature

$\Delta \mathrm{G}=\Delta \mathrm{H}-\mathrm{T} \Delta \mathrm{S}$ It is only possible when $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ both are positive.

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Exam: JEE Main 2025
Paper: 24 January, Morning Shift
Subject: Chemistry
Chapter: Thermodynamics & Thermochemistry
Topic: Gibbs Free Energy and the Third Law of Thermodynamics

Standard entropies of X 2, Y 2 and X Y 5 are 70, 50 and 110 J K^-1 mol^-1 respectively. The temperature in Kelvin at which the reaction 1/2…

Answer: A

Step-by-step solution

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