The First Principle of Thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed but only transformed from one form to another. In a thermodynamic system, the change in internal energy results from the exchange of heat and work with the surroundings.
dU = \delta Q - \delta W
This relation shows that the variation of the internal energy of a system equals the heat supplied to the system minus the work done by the system. The first law is essential for analyzing thermodynamic processes and understanding how energy is transferred during physical and chemical transformations. It is widely applied in physics, chemistry, and engineering to perform energy balance calculations and to study the efficiency of thermodynamic systems.