Kelvin-Planck statement , it is impossible for a system to carry out a cyclical process whose only effects are the flow of heat from a heat source to the system and the performance, by the system, of an equivalent amount of work.
The second law prevents the existence of a machine capable of converting all the heat it absorbs into work during a cyclical process.
A heat source (or heat source) is understood to be a body large enough so that the heat flow between it and the system does not cause a change in temperature at the source (the ocean is a good source of heat).
Clausius statement, It is impossible for a system to carry out a cyclic process whose only effects are the flow of heat into the system from a cold source and the flow of an equal amount of heat from the system to the hot source.
The Clausius system is a refrigerating machine and in order to function it requires work to be done on the system.