Practice question

**Heat engine** absorbs Q_h from hot reservoir T_h, does work W, rejects Q_c to cold T_c, efficiency η = W/Q_h =1 - Q_c/Q_h, second law limits η <1, Kelvin-Planck forbids perfect engine with Q_c=0, Clausius statement heat cannot flow spontaneously from cold to hot without work, equivalent to Kelvin-Planck. Δ U = μ C_v Δ T . μ = 0.3 , C_v = 20.8 , Δ T = 340 - 280 = 60 . Δ U = 0.3 × 20.8 × 60 = 374.4 J ≈ 374 J . Using first law ΔU = Q - W, W = ∫ P dV, isobaric W =