What is first law of thermodynamics

Solution:

First law of thermodynamics states that energy can neither be created nor be destroyed. It can only be converted from one form to other. It is a different form of law of conservation of energy. Thus heat and work are different forms of energy which are interconvertible.
1st law:
            $\Delta U=q+w$
$\Delta \cup$ =  change in internal energy
q = heat transfer
w = work done