Planck’s Statement-“ It is impossible to construct a heat engine operating on a cycle, that will extract heat from a reservoir and perform an equivalent amount of work”.

This statement implies that the working substance, working in a cycle, cannot convert 100% of heat extracted into work, i.e., some of  the heat extracted has to be rejected to the sink.

Statement of the second law of thermodynamics starts from “it is impossible.” Thus the second law is negative in from. Hence, it cannot be proved directly. However, the law is accepted universally and has been applied to a wide variety of phenomena like chemical reactions, thermoelectricity, electric, cells, study of solutions, change of state etc.