@property<EOL><INDENT>def rhog_STP(self):<DEDENT>
Vmg = self.Vmg_STP<EOL>if Vmg:<EOL><INDENT>return Vm_to_rho(Vmg, self.MW)<EOL><DEDENT>return None<EOL>
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