Q.17 Calculate maximum work done when 32 g of oxygen expanded isothermally and reversibly from pressure 2 bar to 1 bar at 298 K.
Best answer
Answer: \(W_{max} = -1717\) J \(\approx -1.72\) kJ
Given: mass of O2 = 32 g, M = 32 g mol–1, so \(n = 1\) mol; \(P_1 = 2\) bar, \(P_2 = 1\) bar, \(T = 298\) K, \(R = 8.314\) J K–1 mol–1.
\(W_{max} = -2.303\,nRT\log_{10}\dfrac{P_1}{P_2}\)
\(= -2.303 \times 1 \times 8.314 \times 298 \times \log_{10} 2\)
\(= -2.303 \times 8.314 \times 298 \times 0.3010 = -1717\) J
The negative sign shows that work is done by the gas on the surroundings.
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