23. The Second Law of Thermodynamics

An aluminum can, with negligible heat capacity, is filled with 450 g of water at 0°C and then is brought into thermal contact with a similar can filled with 450 g of water at 50°C. Find the change in entropy of the system if no heat is allowed to exchange with the surroundings. Use ∆S = ∫ dQ / T.

Why would you expect the total entropy change in a Carnot cycle to be zero? Do a calculation to show that it is zero.

(II) A real heat engine working between heat reservoirs at 970 K and 650 K produces 550 J of work per cycle for a heat input of 2500 J. Compare the efficiency of this real engine to that of an ideal (Carnot) engine.