Some experimental values of Z are plotted in Fig. 1.14. At very low pressures, all the
gases shown have Z ≈ 1 and behave nearly perfectly. At high pressures, all the gases
have Z > 1, signifying that they have a larger molar volume than a perfect gas.
Repulsive forces are now dominant. At intermediate pressures, most gases have Z < 1,
indicating that the attractive forces are reducing the molar volume relative to that of a
perfect gas.