could anyone explain me the fundamental different between internal energy and enthalpy? I searched and found the below definitions for both terms. INTERNAL ENERGY:In thermodynamics, the internal energy is the energy contained by a thermodynamic system. ENTHALPY:Enthalpy is a measure of the total energy of a thermodynamic system. I really couldn't find the differences.Is enthalpy a subset of internal energy or internal energy a subset of enthalpy?