Gas phase chemical equilibrium in dinitrogen trioxide and dinitrogen tetroxide |
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Authors: | Jing Chao Randolph C. Wilhoit Bruno J. Zwolinski |
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Affiliation: | Thermodynamics Research Center, Department of Chemistry, Texas A & M University, College Station, Texas 77840 U.S.A. |
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Abstract: | The ideal gas chemical thermodynamic properties for NO, NO2, N2O3, and N2O4 for the temperature range 50 to 5000 K were evaluated by the statistical thermodynamic method using the most recent molecular parameters. In the calculations for NO and NO2, the effects of anharmonicity and vibration—rotation interaction were included. The contributions due to centrifugal distortion were also included for NO2. For evaluation of the thermodynamic properties for N2O3 and N2O4 molecules, the rigid-rotor and harmonic-oscillator model were adopted. A free internal rotation was assumed for N2O3 and an internal rotation barrier height (V2) of 1.58 kcal mol−1 was derived for N2O4. The thermodynamic properties due to hindered internal rotation were clculated using a partition function formed by summation of internal rotation energy levels. The thermodynamic properties for two equilibrium mixtures: NO2---N2O4 and N2O3---NO---NO2---N2O4 were also calculated. The effects of temperature and pressure on heat capacities and compositions of these two mixtures are illustrated graphically and the calculated heat capacities and equilibrim constants are in good agreement with available experimental values. |
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