 During the cycle, an arbitrary amount of entropy Δ"S" is extracted from the hot reservoir, and deposited in the cold reservoir.Since there is no volume change in either reservoir, they do no work, and during the cycle, an amount of energy "T"hΔS is extracted from the hot reservoir and a smaller amount of energy "T"cΔS is deposited in the cold reservoir.The difference in the two energies (Th-Tc)ΔS is equal to the work done by the engine.