For example, to evaluate enthalpy change between two points h (v 1, T 1) and h (v 2, T 2) we first compute the enthalpy departure function between volume v 1 and infinite volume at T = T 1, then add to that the ideal gas enthalpy change due to the temperature change from T 1 to T 2, then subtract the departure function value between v 2 and infinite volume.