High Temperature Heat Capacity of Gaseous Species

The thermodynamic data of gaseous species have been extensively investigated in the relation with the high temperature glass forming materials. In many cases, only the enthalpy of formation at 298 K is reported from the vapor pressure mesurement with Mass spectrometer. Usually, heat capacities of gaseouos species are evaluated from the molecular constants. Even so, for complicated molecules such as metal oxisalt species, such investigations are quite limited compared with a number of available enthalpy values. Thus, a very simple method is adopted to estimate the heat capacities for such species.

1. Literature
   217. Emelyanova, K.A., Shugurov, S.M., Panin, A.I., Lopatin, S.I., J. Chem.Thermodyn. 101, 337-342 2016.
   339.
          (a) Gingerich, KA., Miller, F., J. Chem. Phys. 63, 1211-1217 2008.
          (b) Pupp, C., Gingerich, KA., J. Chem. Phys. 54, 3380-3384 1971.
          (c) Lopatin, SI., Shugurov, SM., Open Thermodyn. J. 7(Suppl. 1, M5) 35-36 2013.
                 Review articles with many references.
          (d) Shugurov, SM., Lopatin, SI., Stolyarova, VL., Russ. J. Gener. Chem. 76(3), 340-345 2006.
          (e) Emelyanova, KA., Shugurrov, SM., Panin, AI., Lopatin, SI. J. Chem. Thermodyn. 101, 337-342 2016.
          (f)Lopatin, SI., Shugurov, SM., Panin,AI., J. Mass Spectrom. 54, 507-519 2019.
          (g) Yokokawa, H., estimation of S and Cp, 2022-2023.
   346. Lopatin, SI., Shugurov, SM., Panin, AI., Rapid. Commun. Mass Spectrom. 30, 2027-2032 2016.
   
   
   
2. Estimation method
   Estimation for the metal oxysalt vapors is made by constructing the formation reaction from the metal oxide vapor (A2O, BO, C2O3 etc ) and the other vapors(B2O3, P2O3, PO2, SiO, SiO2, N2O3, N2O5,CO2).
   1. Entropy
      The entropy changes for the above formation reaction are assumed to change smoothly with atomic radii of the metal for respective acidic vapors. From the known values from the well investigated compounds, the entropy for respective vapors are estimated with appropriate extrapolation.
      
      • One Eaxmple: 0.5A2O + 0.5N2O3(N2O5,B2O3,P2O3,P2O5) = ANO2(ANO3,ABO2,APO2,APO3)
        
        Table Known and Estimated Entropies of Reactions given in J/K mol
        Red values are estimated from the known black values.

        Alkali	Radii	ANO2(g)	ANO3(g)	ABO2(g)	APO2(g)	APO3(g)
        Li	0.76	14.34	-12	17.038	12	-11
        Na	1.02	-2.006	-13.436	8.508	-3.914	-12.634
        K	1.35	4	-8.492	12.357	2	-7
        Rb	1.5	10.43	-2.426	14.313	8	-1
        Cs	1.7	11.577	-1.825	12.708	9	-0.5

        
        
      
      
   2. Heat Capacity
      The sum of the heat capacities of the constituent vapors is adopted.
   3. Characterisitic Features
      As a result of above assumptions, the entropy changes of the above formation reaction is always constant independently of temperature.

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