Q86 · CSIR NET Chemistry, June 2019
Paper: CSIR NET June 2019 · Subject: Physical Chemistry · Chapter: Thermodynamics · Topic: Laws State Functions · Marks: 2 · Difficulty: Medium
A sample of 2.0 moles of $\mathrm{O}_{2}(\mathrm{g})$ (assumed ideal) at 500 K is expanded from 5 L to 50 L under adiabatic and reversible conditions. The change in its internal energy (in kJ) is close to $\mathrm{R}=8.3 \mathrm{K}^{-1} \mathrm{mol}^{-1} ; \mathrm{C}_{\mathrm{V}, \mathrm{m}}=\frac{5}{2} \mathrm{R}$
(a)-22.5
(b)-12.5
(c)-19.1
(d)-7.5
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Reversible adiabatic: T₂ = T₁(V₁/V₂)^{R/C_V} = 500 × 0.1^{0.4} = 199 K; ΔU = nC_VΔT = 2 × 20.75 × (−301) = −12.5 kJ.
Study loop for Thermodynamics