GATE 2020 CY – Question 62
Gaseous CO has van der Waals a = 1.49 L² atm/mol² and b = 0.0399 L/mol. Find fugacity at 35°C and 95 atm in atm, to 2 decimals. R = 0.082 L atm/(mol K).
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Correct answer: 88.11 to 88.60
Explanation
The intended low-pressure virial approximation to van der Waals gives $B(T)=b-a/(RT)$ and $\ln(f/P)\approx BP/(RT)$. At T ≈ 308 K, B ≈ −0.01910 L/mol, so $\ln(f/95)\approx-0.0719$ and f ≈ 88.4 atm, in the official 88.11–88.60 range. A full high-pressure van der Waals fugacity calculation is a different approximation; the quoted source key uses the leading-virial form even at this pressure.
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