One mole of a gas obeys PV = RT + BP with B = 3 L/mol, independent of temperature, and its internal energy depends on temperature only. The gas is isothermally expanded from 13 L to 23 L against a con

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One mole of a gas obeys PV = RT + BP with B = 3 L/mol, independent of temperature, and its internal energy depends on temperature only. The gas is isothermally expanded from 13 L to 23 L against a constant external pressure of 1 bar at 200 K. Take R = 0.1 L-bar/K-mol. The change in enthalpy of the gas is approximately

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Δ U = 0, so Δ H = Δ(PV) = B Δ P. RT = 0.1 × 200 = 20 L-bar. P 1 = RT/(V 1 - B) = 20/10 = 2 bar; P 2 = 20/20 = 1 bar. Δ P = -1 bar. Δ H = 3 × (-1) = -3 L-bar = -300 J. Matches (b).

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