The First Law of Thermodynamics is a statement of the Law of Conservation of Energy for thermodynamic systems.

• It states that the change in internal energy ($\Delta U$) of a system is equal to the heat added ($Q$) to the system minus the work done ($W$) by the system: $\Delta U=Q-W$ (Standard Physics convention)
• Internal energy is a state function, meaning it depends only on the initial and final states, not the path taken.