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BITSAT 2021
Exam
BITSAT
Year
2021
Subject
Chemistry
Chapter
Thermodynamics (C)

BITSAT 2021 · Chemistry · Thermodynamics (C)

Work out the heat change (cal) when 40 g of He gas at 27^ ^ C...

Work out the heat change (cal) when 40g40 \mathrm{ g} of He gas at 27∘C27^{{}^{\circ}} \mathrm{C} undergoes isothermal and reversible compression from initial pressure of 1atm1 \mathrm{ atm} to 10 \mathrm{ atm} \left(\mathrm{R}=2 \mathrm{cal} \mathrm{K}^{-1} \mathrm{ mol}^{-1}\right).

Options

  1. A13.818kcal13.818 \mathrm{kcal}
  2. B−13.818kcal-13.818 \mathrm{kcal}
  3. C55.272kcal55.272 \mathrm{kcal}
  4. D−55.272kcal-55.272 \mathrm{k} \mathrm{cal}

Correct answer

B. −13.818kcal-13.818 \mathrm{kcal}

Step-by-step solution

q=−wrev=−(−2.303nRTlog⁡P1P2)=2.303×404×2×300log⁡110=−13.82kcal\begin{aligned} \mathrm{q} &=-\mathrm{w}_{\mathrm{rev}}=-\left(-2.303 \mathrm{nRT} \log \frac{\mathrm{P}_{1}}{\mathrm{P}_{2}}\right) \\ &=2.303 \times \frac{40}{4} \times 2 \times 300 \log \frac{1}{10}=-13.82 \mathrm{kcal} \end{aligned}
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