Laws of Thermodynamics

First law of thermodynamics  is regarding  conservation of energy adapted for thermodynamics system .

"It states that for an isolated system total  energy of the system is remains constant . It can be transformed from one form to another but can neither be created nor destroyed ."

* Mathematically,
                     ΔU = Q - W

"It states that the change in internal energy of the closed system is equal to the amount of heat supplied to the system minus the amount of working by the system on surrounding."

Second law of thermodynamics

It gives general principle for the direction of  heat transfer and attainable efficiencies of heat engines.

Kelvin-planck statement for Heat engines

It is impossible to extract all the heat from the hot reservoir and used into useful work , there will be certainly  heat exhausted to the surrounding .

And which limits the thermal efficiency of the heat engines or precludes the perfect heat engines .

Refrigerator  :
"It is not possible of heat to flow  from cold body to warmer body without any work done on the system for this flow."

Entropy  :
In any cyclic process Entropy of the isolated system is either increasing or remains same .

Third law of Thermodynamics
It states that for the perfect crystal entropy is zero at absolute zero kelvin temperature.

Note : The crystal should be perfect and temperature should be absolute zero kelvin otherwise there will be a thermal motion within the crystal .