Q52 · CSIR-NET Chemistry, December 2019

Paper: CSIR-NET December 2019 · Subject: Physical Chemistry · Chapter: Thermodynamics · Topic: Laws State Functions · Marks: 2 · Difficulty: Medium

Consider the entropy changes in a system undergoing transformation, as depicted in the diagram, below
\[ \begin{array}{c} 25^{\circ}\mathrm{C} \xrightarrow{\Delta S_1} 50^{\circ}\mathrm{C} \xrightarrow{\Delta S_2} 75^{\circ}\mathrm{C} \\ 25^{\circ}\mathrm{C} \xrightarrow{\Delta S} 75^{\circ}\mathrm{C} \end{array} \]
The correct statement among the following is
(a)$\Delta S_1 = \Delta S_2$ and $\Delta S \neq \Delta S_1 + \Delta S_2$
(b)$\Delta S_1 > \Delta S_2$ and $\Delta S \neq \Delta S_1 + \Delta S_2$
(c)$\Delta S_1 = \Delta S_2$ and $\Delta S = \Delta S_1 + \Delta S_2$
(d)$\Delta S_1 > \Delta S_2$ and $\Delta S = \Delta S_1 + \Delta S_2$
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
ΔS = C_p ln(T₂/T₁): 25→50 °C gives ln(323/298) = 0.081 C_p, larger than 50→75 °C, ln(348/323) = 0.075 C_p. Entropy is a state function, so ΔS = ΔS₁ + ΔS₂: statement (4).

Study loop for Thermodynamics

1. Practise the PYQsPrevious-year questions, with answers

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