Practice question

**Energy transfer** first law ΔU = Q - W, W includes P-V work, shaft work, electrical work, Q includes conduction Fourier law, convection, radiation Stefan-Boltzmann, distinction important because work is controllable, heat spontaneous from hot to cold, entropy associated with heat not work, explaining why heat engine efficiency <100%. W = (μ R (T₁ - T₂))/(γ - 1) . μ = 2 , R = 8.3 , T₁ = 700 , T₂ = 350 , γ = 1.67 . W = (2 × 8.3 × (700 - 350))/(1.67 - 1) = (16.6 × 350)/(0.67) ≈ 8671.6 J ≈ 8672 J . Using first law ΔU