During the phase change of a pure substance:

Which among the following relations is/are valid ONLY for reversible process undergone by a pure substance?

Figure below shows a reversible heat engine $${E_R}$$ having heat interactions with three constant temperature systems. Calculate the thermal efficiency of the heat engine.

The equivalent evaporation $$(kg/hr)$$ of a boiler producing $$2000$$ $$kg/hr$$ of steam with enthalpy content of $$2426$$ $$kJ/kg$$ from feed water at temperature $${40^ \circ }C$$ (liquid enthalpy $$=168$$ $$kJ/kg$$) is (Enthalpy of vaporization of water at $${100^0}C = 2258$$ $$kJ/kg$$).