Enthalpy is an extensive property ; it is proportional to the size of the system (for homogeneous systems). As intensive properties, the specific enthalpy, h = ⁠ H / m ⁠ , is referenced to a unit of mass m of the system, and the molar enthalpy, H m = ⁠ H / n ⁠ , where n is the number of moles. For inhomogeneous systems the enthalpy is the sum of the enthalpies of the component subsystems: H = ∑ ∑ k H k , where