code: def Zg(self):
          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
          '''
          Vmg = self.Vmg
          if Vmg:
              return Z(self.T, self.P, Vmg)
          return Nonf Zg(self):
          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
          '''
          Vmg = self.Vmg
          if Vmg:
              return Z(self.T, self.P, Vmg)
          return None
docs: 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