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Reaction Rate Coefficients (reaction + rate_coefficient)
Selected AbstractsDetermination of the rate coefficients of the SO2 + O + M , SO3 + M reactionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2010S. M. Hwang Rate coefficients of the title reaction R31 (SO2 + O + M , SO3 + M) and R56 (SO2 + HO2, SO3 + OH), important in the conversion of S(IV) to S(VI), were obtained at T = 970,1150 K and ,ave = 16.2 ,mol cm,3 behind reflected shock waves by a perturbation method. Shock-heated H2/O2/Ar mixtures were perturbed by adding small amounts of SO2 (1%, 2%, and 3%) and the OH temporal profiles were then measured using laser absorption spectroscopy. Reaction rate coefficients were elucidated by matching the characteristic reaction times acquired from the individual experimental absorption profiles via simultaneous optimization of k31 and k56 values in the reaction modeling (for satisfactory matches to the observed characteristic times, it was necessary to take into account R56). In the experimental conditions of this study, R31 is in the low-pressure limit. The rate coefficient expressions fitted using the combined data of this study and the previous experimental results are k31,0/[Ar] = 2.9 × 1035 T,6.0 exp(,4780 K/T) + 6.1 × 1024 T,3.0 exp(,1980 K/T) cm6 mol,2 s,1 at T = 300,2500 K; k56 = 1.36 × 1011 exp(,3420 K/T) cm3 mol,1 s,1 at T = 970,1150 K. Computer simulations of typical aircraft engine environments, using the reaction mechanism with the above k31,0 and k56 expressions, gave the maximum S(IV) to S(VI) conversion yield of ca. 3.5% and 2.5% for the constant density and constant pressure flow condition, respectively. Moreover, maximum conversions occur at rather higher temperatures (,1200 K) than that where the maximum k31,0 value is located (,800 K). This is because the conversion yield is dependent upon not only the k31,0 and k56 values (production flux) but also the availability of H, O, and HO2 in the system (consumption flux). © 2010 Wiley Periodicals, Inc., Int J Chem Kinet 42: 168,180, 2010 [source] The analytical resolution of parallel first- and second-order reaction mechanismsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2010N. B. Caballero Given the species A1 and A2, the competition among the three different elementary processes (1) (2) (3) is frequently found in thermal and photochemical reaction systems. In the present paper, an analytical resolution of the system (1),(3), performed under plausible contour conditions, namely, finite initial molar concentrations for both reactants, [A2]0 and [A1]0, and nonzero reaction rate coefficients k1, k2, and k3, leads to the equation [A1] = ((,[A2], , [A2])/,) , ,, where , = k1/2k3, , = , + 1 = 2k3/k2, and , = ([A2]0 + ,[A1]0 + , ,))/[A2]0,. The comparison with a numerical integration employing the fourth-order Runge,Kutta algorithm for the well-known case of the oxidation of organic compounds by ferrate ion is performed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 562,566, 2010 [source] Kinetics of the reactions of C2H5, n -C3H7, and n -C4H9 radicals with Cl2 at the temperature range 190,360 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2007Arkke J. Eskola The kinetics of the C2H5 + Cl2, n -C3H7 + Cl2, and n -C4H9 + Cl2 reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time-resolved measurements to obtain reaction rate coefficients under pseudo-first-order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5,5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C2H5 + Cl2) = (1.45 ± 0.04) × 10,11 (T/300 K),1.73 ± 0.09 cm3 molecule,1 s,1 (190,359 K), k(n -C3H7 + Cl2) = (1.88 ± 0.06) × 10,11 (T/300 K),1.57 ± 0.14 cm3 molecule,1 s,1 (204,363 K), and k(n -C4H9 + Cl2) = (2.21 ± 0.07) × 10,11 (T/300 K),2.38 ± 0.14 cm3 molecule,1 s,1 (202,359 K), with the uncertainties given as one-standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C2H5 + Cl2 reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work and in previous determinations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 614,619, 2007 [source] Ab Initio Group Contribution Method for Activation Energies of Hydrogen Abstraction ReactionsCHEMPHYSCHEM, Issue 1 2006Mark Saeys Prof. Abstract The group contribution method for activation energies is applied to hydrogen abstraction reactions. To this end an ab initio database was constructed, which consisted of activation energies calculated with the ab initio CBS-QB3 method for a limited set of well-chosen homologous reactions. CBS-QB3 is shown to predict reaction rate coefficients within a factor of 2,4 and Arrhenius activation energies within 3,5 kJ,mol,1of experimental data. Activation energies in the set of homologous reactions vary over 156 kJ,mol,1with the structure of the abstracting radical and over 94 kJ,mol,1with the structure of the abstracted hydrocarbon. The parameters required for the group contribution method, the so-called standard activation group additivity values, were determined from this database. To test the accuracy of the group contribution method, a large set of 88 additional activation energies were calculated from first principles and compared with the predictions from the group contribution method. It was found that the group contribution method yields accurate activation energies for hydrogen-transfer reactions between hydrogen molecules, alkylic hydrocarbons, and vinylic hydrocarbons, with the largest deviations being less than 6 kJ,mol,1. For reactions between allylic and propargylic hydrocarbons, the transition state is believed to be stabilized by resonance effects, thus requiring the introduction of an appropriate correction term to obtain a reliable prediction of the activation energy for this subclass of hydrogen abstraction reactions. [source] | ||||||||||