code: def Um(self):
          r'''Internal energy of the chemical at its current temperature and
          pressure, in units of [J/mol].
  
          This property requires that :obj:`thermo.chemical.set_thermo` ran
          successfully to be accurate.
          It also depends on the molar volume of the chemical at its current
          conditions.
          '''
          return self.Hm - self.P*self.Vm if (self.Vm and self.Hm is not None) else Nonf Um(self):
          r'''Internal energy of the chemical at its current temperature and
          pressure, in units of [J/mol].
  
          This property requires that :obj:`thermo.chemical.set_thermo` ran
          successfully to be accurate.
          It also depends on the molar volume of the chemical at its current
          conditions.
          '''
          return self.Hm - self.P*self.Vm if (self.Vm and self.Hm is not None) else None
docs: r'''Internal energy of the chemical at its current temperature and
          pressure, in units of [J/mol].
  
          This property requires that :obj:`thermo.chemical.set_thermo` ran
          successfully to be accurate.
          It also depends on the molar volume of the chemical at its current
          conditions.