Thermochemical equations internal energy

The equation of state for the combustion products was approximated as an ideal gas p = pRT, and a constant specific heat internal energy e = CyT was used for simplicity. The value of Cy/R was determined by fitting the internal energy expression to the results of detailed thermochemical computations of the states along the isentrope passing through the CJ point. The STANJAN chemical equilibrium code and JANNAF data for the product species CO2, CO, H2O, H2, O2, 0, H, HO2, and H2O2 were used in this computation. 

The appearance energy (AE) is the minimum energy required to photoionize and fragment the molecule AB in the reaction shown in Equation [2] and, in the absence of any excess internal energy, can provide useful thermochemical information about the reactant and products. 

The activation energies are in reasonable agreement with the experimental data for Arrhenius equations. The preexponential factors, however, are not so good. A better agreement is obtained with the modified Arrhenius equation. Now, the preexponential factors and temperature dependence are reasonable, and activation energies are not far from experimental value (MADs are under 1 kcal/mol). From a kinetic point of view, however, the description is semiquantitative at best. If one plots the rate constants obtained theoretically and experimentally for these reactions, the picture shown in Fig. 3 is obtained. There is a quite a difference between experimental and theoretical data at each temperature, which could be adjusted by a simple multiplicative factor for each reaction. The calculations predict that the ratio of formation of the 1-propyl radical to the 2-propyl radical would be about 5 times faster theoretically than observed experimentally. Both theoretically and experimentally, one observes that increase in the temperature equalizes the rate of formation of both radicals, but experimentally this happens faster than what the theoretical calculations predict. This failure is not corrected even considering internal rotation to perform more precise thermochemical calculations. 

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