A student constructs a laboratory heat engine that is intended to convert thermal energy completely into mechanical work.
(i) State the Kelvin–Planck statement of the Second Law of Thermodynamics.
(ii) Using the energy balance relation QH=QC+W, explain why some heat must necessarily be rejected to a colder reservoir when an engine operates in a cycle.
(iii) If an engine were to convert the entire quantity QH absorbed from the hot reservoir into work with QC=0, describe qualitatively what would happen to the total entropy of the universe. Comment on the feasibility of such an engine in the light of the Second Law.