Practice question

**Carnot engine** reversible engine operating between T_h and T_c has maximum efficiency η =1 - T_c/T_h, T in kelvin, e.g., T_h=400 K T_c=300 K η=0.25, real engines less due to irreversibilities, second law defines direction of spontaneous processes and entropy increase. First Law: Δ Q = Δ U + Δ W . Δ Q = -500 J (heat released), Δ W = -200 J (work on system). -500 = Δ U - 200 ⇒ Δ U = -500 + 200 = -300 J . Using first law ΔU = Q - W, W = ∫ P dV, isobaric W = P ΔV, isothermal W =