code: def rhog_STP(self):
          r'''Gas-phase mass density of the mixture at 298.15 K and 101.325 kPa,
          and the current composition in units of [kg/m^3].
  
          Examples
          --------
          >>> Mixture(['nitrogen'], ws=[1]).rhog_STP
          1.145534453639403
          '''
          Vmg = self.Vmg_STP
          if Vmg:
              return Vm_to_rho(Vmg, self.MW)
          return Nonf rhog_STP(self):
          r'''Gas-phase mass density of the mixture at 298.15 K and 101.325 kPa,
          and the current composition in units of [kg/m^3].
  
          Examples
          --------
          >>> Mixture(['nitrogen'], ws=[1]).rhog_STP
          1.145534453639403
          '''
          Vmg = self.Vmg_STP
          if Vmg:
              return Vm_to_rho(Vmg, self.MW)
          return None
docs: r'''Gas-phase mass density of the mixture at 298.15 K and 101.325 kPa,
          and the current composition in units of [kg/m^3].
  
          Examples
          --------
          >>> Mixture(['nitrogen'], ws=[1]).rhog_STP
          1.145534453639403