First law of thermodynamics:

The First Law of Thermodynamics states that work and heat are equally convertible. The present tendency is to include all the forms of energy. The First Law can be stated in a number of ways:

1. Energy can neither be created nor destroyed; but it can be conserved from one form to another.

2. All energy which goes into system comes out in some form or the other. Energy does not disappear and has the ability to be converted into any other form of the energy.

3. If system is carried through cycle, the summation of work delivered to surroundings is equal to summation of heat taken from surroundings.

4. No machine can generate energy without corresponding expenditure of energy.

5. Total energy of isolated system in all the form, remain constant

The first law of thermodynamics cannot be proved mathematically.