Statements of Second Law of Thermodynamics

The second law of thermodynamics is stated in two ways. (i) Kelvin-Planck statement and (ii) Clausius statement.

STATEMENTS OF SECOND LAW OF THERMODYNAMICS

The second law of thermodynamics is stated in two ways.

(i) Kelvin-Planck statement and

(ii) Clausius statement.

1. Kelvin-Planck Statement

The Kelvin-Planck statement can be expressed as "it is impossible for any device that operates on a cyclic process to receive heat from a single reservoir and produce an equivalent amount of work".

Otherwise, it is impossible to construct an engine working on a cyclic process which converts the entire heat energy supplied into equivalent amount of useful work. Simply, it can be stated that the entire heat energy given to an engine cannot be converted it into useful work and some amount of heat energy will be rejected to sink.

The Kelvin-Planck statement can also be expressed as no heat engine can have a thermal efficiency of 100 %.

2. Clausius Statement

The Clausius statement is expressed as "it is impossible to construct an operating device working on a cyclic process which produces no other effect than the transfer of energy as heat from a low temperature body to a high temperature body".

The Clausius statement can also be stated as "heat cannot flow from cold reservoir to hot reservoir without any external aid but it can flow from hot reservoir to cold reservoir without any external aid."