The work done during reversible isothermal expansion of one mole of hydrogen gas at 25^°C from pressure of 20 atmosphere to 10 atmosphere is:(Given R = 2.0 cal K^-1 mol^-1)

1. 100 calories

2. 0 calorie

3. $-$ 413.14 calories

4. 413.14 calories

Doubtly Asked 30 Oct 2026 NEET UG 2024 Practice test neet Save WhatsApp Report

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Answer: 3. $-$ 413.14 calories

Key idea: for reversible isothermal expansion, $w=-2.303\,nRT\log\dfrac{P_1}{P_2}$ (work done by the gas is negative in this convention).

$$w=-2.303\times1\times2\times298\times\log\frac{20}{10}=-2.303\times596\times0.3010\approx-413.14\ \mathrm{cal}$$

Option 3.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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