The first law of thermodynamics is a statement of energy conservation in the context of thermodynamics. The first law states that a system’s internal energy can be changed either by heat flow to the system, by doing mechanical work on the system, or by a combination of the 2. Although there are infinitely many ways to combine work and heat, specific thermodynamic processes—including isothermal and adiabatic processes—prove useful for understanding thermal energy flows. These processes are particularly simple to analyze when applied to ideal gases.