(a) State the Kelvin–Planck and Clausius statements of the second law of thermodynamics.
(b) Give a reason why the change in entropy of a system that completes a thermodynamic cycle is zero, even if the individual processes within the cycle are irreversible.
(c) If a cyclic device receives heat from a high-temperature reservoir and rejects heat to a low-temperature reservoir, explain with suitable reasoning why the total entropy change of the universe must be positive for the device to be irreversible and zero for the device to be reversible.