According to Second law the engine based on the cyclic process is not possible in which we can convert all the heat into the work. There are a number of statements for the second law but the two most common statements are.

1.      Kelvin plank statement

2.      Clausius Statement 

Kelvin plank statement: No process is possible whose sole result is the absorption of heat from a reservoir and the conversion of all of this heat into work.

Clausius Statement: No process is possible whose sole result is the transfer of heat from a colder to a hotter body.