Practice question

**Second law Kelvin-Planck statement** no process possible whose sole result is absorption of heat from reservoir and complete conversion to work, heat engine must have at least two reservoirs hot and cold, efficiency η = W/Q_h =1 - Q_c/Q_h <1, impossible 100% efficient, Carnot efficiency η_Carnot =1 - T_c/T_h maximum possible between T_h and T_c. Δ Q = m s Δ T . m = 0.6 , s = 386.4 , Δ T = 50 - 20 = 30 . Δ Q = 0.6 × 386.4 × 30 = 6955.2 J ≈ 6955 J . Using first law ΔU = Q - W, W =