The First Law of Thermo dynamics

Generally it is also known as Law of Conservation of Energy.
Statement:- " Energy can be neither created nor destroyed although it may be transformed from one form to another."
The law may also be stated as," The total energy of the universe, i.e. system and surroundings taken together is always constant during any physical or chemical process."
Mathematical expression ot the Law:-
dU= q + w; where dU= change in internal energy of the system;
Since w= - p dV
Hence, dU = q - p dV