Chemistry - Thermodynamics - II Question with Solution | TestHub
ChemistryThermodynamics - IICalculation of DSHard2 minQB
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The molar heat capacity of CD4 (deuterated methane) vapour at constant pressure is 12 cal/K-mol; treat it as an ideal gas with R = 2 cal/K-mol. 8.0 g of CD4 is cooled at constant pressure from 800 K to 400 K and then heated at constant volume from 400 K to 600 K. The total entropy change is (ln 2 = 0.7, ln 3 = 1.1)
Options:
Answer:
B
Solution:
Molar mass of CD4 = 12 + 4(2) = 20 g/mol, n = 8.0/20 = 0.4 mol. CV = CP - R = 10 cal/K-mol. Step 1: Δ S1 = nCPln(400/800) = 0.4 × 12 × (-0.7) = -3.36 cal/K. Step 2: Δ S2 = nCVln(600/400) = 0.4 × 10 × ln 1.5 = 0.4 × 10 × (1.1 - 0.7) = +1.60 cal/K. Total = -3.36 + 1.60 = -1.76 cal/K. Matches (b).
Stream:JEESubject:ChemistryTopic:Thermodynamics - IISubtopic:Calculation of DS
⏱ 2mℹ️ Source: QB
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