code: def Cvgm(self):
          r'''Gas-phase ideal-gas contant-volume heat capacity of the mixture at
          its current temperature and composition, in units of [J/mol/K]. Subtracts R from
          the ideal-gas heat capacity; does not include pressure-compensation
          from an equation of state.
  
          Examples
          --------
          >>> Mixture(['water'], ws=[1], T=520).Cvgm
          27.13366316134193
          '''
          Cpgm = self.HeatCapacityGasMixture(self.T, self.P, self.zs, self.ws)
          if Cpgm:
              return Cpgm - R
          return Nonf Cvgm(self):
          r'''Gas-phase ideal-gas contant-volume heat capacity of the mixture at
          its current temperature and composition, in units of [J/mol/K]. Subtracts R from
          the ideal-gas heat capacity; does not include pressure-compensation
          from an equation of state.
  
          Examples
          --------
          >>> Mixture(['water'], ws=[1], T=520).Cvgm
          27.13366316134193
          '''
          Cpgm = self.HeatCapacityGasMixture(self.T, self.P, self.zs, self.ws)
          if Cpgm:
              return Cpgm - R
          return None
docs: r'''Gas-phase ideal-gas contant-volume heat capacity of the mixture at
          its current temperature and composition, in units of [J/mol/K]. Subtracts R from
          the ideal-gas heat capacity; does not include pressure-compensation
          from an equation of state.
  
          Examples
          --------
          >>> Mixture(['water'], ws=[1], T=520).Cvgm
          27.13366316134193