@property<EOL><INDENT>def Zg(self):<DEDENT>
Vmg = self.Vmg<EOL>if Vmg:<EOL><INDENT>return Z(self.T, self.P, Vmg)<EOL><DEDENT>return None<EOL>
r'''Compressibility factor of the chemical in the gas phase at the
        current temperature and pressure, [dimensionless].

        Utilizes the object oriented interface and
        :obj:`thermo.volume.VolumeGas` to perform the actual calculation of
        molar volume.

        Examples
        --------
        >>> Chemical('sulfur hexafluoride', T=700, P=1E9).Zg
        11.140084184207813