Second law of thermodynamics

First law of thermodynamics does not give full information about the relation between mechanical work and heat, i.e., this law does not give idea about the condition under which conversion of heat into work or vice versa can take place and also it does not give the idea about the direction in which the transfer of heat take place.

The fundamental law in nature is heat always passes from hot body to cold body by itself. This can be stated in number of ways.
Classius states that it is impossible for a self acting machine unaided by any external agency to transfer heat from cold body to hot body i.e., from a body at lower temperature to a body at higher temperature.
Kelvins states this law in another way that it is impossible to continuously extract of work from cool body to temperature lower than that of the coldest of its surroundings. Therefore, no engine can convert the whole of the heat energy supplied to it into useful work. Under this concept, Kelvin stated the second law of thermodynamics that it is impossible to construct a heat engine which converts heat energy completely into work without any change in the working system.
Can you know what are the tremendous changes happen if second law of thermodynamics is not valid? if second law of thermodynamics is not valid, then every substance in the universe becomes ready to give out heat energy completely to do work whatever heat energy absorbed by it. Then endless source of energy available in the universe. But this is impossible.