Q31 · CSIR-NET Chemistry, December 2011

Paper: CSIR-NET December 2011 · Subject: Physical Chemistry · Chapter: Thermodynamics · Topic: Thermodynamics – General · Marks: 2 · Difficulty: Medium

Under review — part of this question (a structure or an option) is not clear in the source scan. 4AB is checking it against the original book; the answer shown may change.
For the reaction $\mathrm{H}_{2} \mathrm{O}(\mathrm{g})+\mathrm{C}$ (graphite) $\leftrightharpoons \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$, the variation of energy parameter $\Delta \mathrm{G}^{\mathrm{0}}$, $\Delta \mathrm{H}^{\mathrm{0}}$ and $\mathrm{T} \Delta \mathrm{S}^{\mathrm{0}}$ of the reaction over a large temperature range is shown below. The correct identification of the curves is given by
(a)$\mathrm{A} \rightarrow \Delta \mathrm{G}$, $\mathrm{B} \rightarrow \Delta \mathrm{H}$, C→TAS
(b)$\mathrm{A} \rightarrow \Delta \mathrm{H} , \mathrm{B} \rightarrow \Delta \mathrm{G}, \mathrm{C} \rightarrow \mathrm{T} \Delta \mathrm{S}$
(c)$\mathrm{A} \rightarrow \Delta \mathrm{G} . \mathrm{B} \rightarrow \mathrm{T} \Delta \mathrm{S}, \mathrm{C} \rightarrow \Delta \mathrm{H}$
(d)$\mathrm{A} \rightarrow \mathrm{TAS}, \mathrm{B} \rightarrow \Delta H, \mathrm{C} \rightarrow \Delta \mathrm{G}$
Answer
Under review — not yet confirmed.
Answer: D
Explanation
ΔH° is nearly constant (horizontal B). ΔS° > 0 (gas is formed), so TΔS° rises (A) and ΔG° = ΔH° − TΔS° falls (C) (d).

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