<P> where the label k refers to the various subsystems . In case of continuously varying p, T or composition, the summation becomes an integral: </P> <Dl> <Dd> H = ∫ ρ h d V, (\ displaystyle H = \ int \ rho h \, dV,) </Dd> </Dl> <Dd> H = ∫ ρ h d V, (\ displaystyle H = \ int \ rho h \, dV,) </Dd> <P> where ρ is the density . </P>

When do you use enthalpy or internal energy