The compressibility factor chart plots the compressibility factor Z, equal to PV/RT, where V is the volume per mole, versus the reduced pressure P_r for several values of the reduced temperature T_r. The reduced pressure and temperature are defined by
P_r = P/PC and T_r = T/T_C, respectively, where P_C is the critical pressure and T_C is the critical temperature. Use buttons to select one of five molecules, and move the black dot to display the compressibility factor curve (blue) for any value of T_r between 1.0 and 1.8. The Z and P_r values for the location of the black dot are displayed on the chart. For an ideal gas, Z = 1 (green line).