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Thermodynamics
Entropy Change in Isothermal Expansion
1 question from 1 paper, each with its answer.
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Concepts tested
- Entropy change for reversible isothermal expansion
All Questions
2002 AIPMT 1 question
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2 mole of ideal gas at $27^\circ C$ temp. is expanded reversibly from 2 lit. to 20 lit. Find entropy change (R = 2 cal/mol K) : -For reversible isothermal expansion of an ideal gas: $\Delta S = nR\ln\dfrac{V_2}{V_1} = 2.303\,nR\log\dfrac{V_2}{V_1}$
$\Delta S = 2.303 \times 2 \times 2 \times \log\dfrac{20}{2}$
$= 2.303 \times 4 \times \log 10 = 2.303 \times 4 \times 1$
$\Delta S = 9.2$ cal K$^{-1}$
(The temperature does not enter the calculation, since the process is isothermal.)