Past exam of the chemistry course of the year 1 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 4 / a / iv

The Clausius statement of the second law forbids a cyclic device whose sole effect is transfer of heat from a colder thermal reservoir to a hotter one. The Kelvin-Planck statement of the second law forbids a cyclic device whose sole effect is complete conversion of heat drawn from a single thermal reservoir into work. These are equivalent formulations of the Second law of thermodynamics; an ordinary refrigerator is allowed because supplied work is an additional effect.