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Arrhenius Parameters (Arrheniu + parameter)
Selected AbstractsIdentification of the effective distribution function for determination of the distributed activation energy models using the maximum likelihood method: Isothermal thermogravimetric dataINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2009Bojan Jankovi The new procedure for identification of the effective distribution function for determination of the distributed activation energy models, which is based on use the maximum likelihood method (MLM), was established. The five different continuous probability functions (exponential, logistic, normal, gamma, and Weibull probability functions (the extended set of distributions)) were used for searching the best reactivity model for two heterogeneous processes: (a) the isothermal reduction process of nickel oxide under hydrogen atmosphere and (b) the isothermal degradation process of bisphenol-A polycarbonate (Lexan) under nitrogen atmosphere. The MLM showed that for both processes, the most suitable reactivity model represents the Weibull distribution model. It was concluded that the values of Arrhenius parameters (ln A and Ea), evaluated from the Weibull distribution model, represent the effective kinetic values for both considered processes. This procedure enables identification the suitable distribution model for considered process only from the experimental data (based on the shapes of obtained integral kinetic curves), and this fact represents the advantage of established analysis. The established mathematical procedure, which is based on the MLM, can be applied as the preliminary analysis for evaluating the distribution of activation energies for complex heterogeneous processes. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 27,44, 2009 [source] Cocatalysis by ruthenium(III) in hydrogen ions catalyzed oxidation of iodide ions: A kinetic studyINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2004Praveen K. Tandon RuCl3 further catalyzes the oxidation of iodide ion by K3Fe(CN)6, already catalyzed by hydrogen ions. The rate of reaction, when catalyzed only by hydrogen ions, was separated graphically from the rate when both Ru(III) and H+ ions catalyzed the reaction. Reactions studied separately in the presence as well as absence of RuCl3 under similar conditions were found to follow second-order kinetics with respect to [I,], while the rate showed direct proportionality with respect to [Fe(CN)6]3,, [RuCl3], and [H+]. External addition of [Fe(CN)6]4, ions retards the reaction velocity, while changing the ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, the extent of the reaction that takes place without adding Ru(III) was calculated and it was in accordance with the values obtained from the reaction in which only H+ ions catalyzed the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate-determining step. Arrhenius parameters at four different temperatures were also calculated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 545,553, 2004 [source] Temperature-dependent kinetic study for ozonolysis of selected tropospheric alkenesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2002Elena V. Avzianova Ozonolysis reactions of alkenes are suggested to play major roles in the chemistry of the troposphere. Rate constants for the gas-phase reactions of O3 with a series of alkenes were determined using relative rate technique based on GC/FID measurements of alkene decays. Experiments were carried out in air over the temperature range of 278,353 K at an atmospheric pressure of 760 Torr. An excess of 1,3,5-trimethylbenzene was used as a HO radical scavenger in all experiments. Arrhenius parameters were calculated for ozonolysis of 1-butene, 1-pentene, 1-hexene, 1-heptene, 2-methyl-1-butene, isobutene, trans -2-butene, trans -2-pentene, cis -2-pentene, trans -2-hexene, cis -2-hexene, 3-chloropropene, 1,1-dichloroethene, and isoprene from temperature-dependent studies of the rate constants. The rate constants obtained in this study are compared with previous literature data. A good linear correlation between the logarithms of the rate constants and calculated HOMO energies of selected alkenes is observed. However, no clear correlation could have been drawn for chlorinated substituted alkenes. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 678,684, 2002 [source] A temperature-dependent kinetics study of the reaction of O(3PJ) with (CH3)2SOINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002F. D. Pope A laser flash photolysis,resonance fluorescence technique has been employed to investigate the kinetics of the reaction of ground state oxygen atoms, O(3PJ), with (CH3)2SO (dimethylsulfoxide) as a function of temperature (266,383 K) and pressure (20,100 Torr N2). The rate coefficient (kR1) for the O(3PJ) + (CH3)2SO reaction is found to be independent of pressure and to increase with decreasing temperature. The following Arrhenius expression adequately describes the observed temperature dependence: kR1(T) = (1.68 ± 0.76) × 10,12 exp[(445 ± 141)/T] cm3 molecule,1 s,1, where the uncertainties in Arrhenius parameters are 2, and represent precision only. The absolute accuracy of each measured rate coefficient is estimated to be ±30%, and is limited predominantly by the uncertainties in measured (CH3)2SO concentrations. The observed temperature and pressure dependencies suggest that, as in the case of O(3PJ) reactions with CH3SH and (CH3)2S, reaction occurs by addition of O(3PJ) to the sulfur atom followed by rapid fragmentation of the energized adduct to products. The O(3PJ) + (CH3)2SO reaction is fast enough so that it could be a useful laboratory source of the CH3SO2 radical if this species is produced in significant yield. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 156,161, 2002; DOI 10.1002/kin.10040 [source] Ab initio investigation on the reaction path and rate for the gas-phase reaction of HO + H2O , H2O + OHJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2003Tadafumi Uchimaru Abstract This article describes an ab initio investigation on the potential surfaces for one of the simplest hydrogen atom abstraction reactions, that is, HO + H2O , H2O + OH. In accord with the findings in the previously reported theoretical investigations, two types of the hydrogen-bonding complexes [HOHOH] and [H2OHO] were located on the potential energy surface. The water molecule acts as a hydrogen donor in the [HOHOH] complex, while the OH radical acts as a hydrogen donor in the [H2OHO] complex. The energy evaluations at the MP2(FC) basis set limit, as well as those through the CBS-APNO procedure, have provided estimates for enthalpies of association for these complexes at 298 K as ,2.1 , ,2.3 and ,4.1 , ,4.3 kcal/mol, respectively. The IRC calculations have suggested that the [H2OHO] complex should be located along the reaction coordinate for the hydrogen abstraction. Our best estimate for the classical barrier height for the hydrogen abstraction is 7.8 kcal/mol, which was obtained from the CBS-APNO energy evaluations. After fitting the CBS-APNO potential energy curve to a symmetrical Eckart function, the rate constants were calculated by using the transition state theory including the tunneling correction. Our estimates for the Arrhenius parameters in the temperature region from 300 to 420 K show quite reasonable agreement with the experimentally derived values. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1538,1548, 2003 [source] Interpretation of the temperature dependence of equilibrium and rate constantsJOURNAL OF MOLECULAR RECOGNITION, Issue 5 2006Donald J. Winzor Abstract The objective of this review is to draw attention to potential pitfalls in attempts to glean mechanistic information from the magnitudes of standard enthalpies and entropies derived from the temperature dependence of equilibrium and rate constants for protein interactions. Problems arise because the minimalist model that suffices to describe the energy differences between initial and final states usually comprises a set of linked equilibria, each of which is characterized by its own energetics. For example, because the overall standard enthalpy is a composite of those individual values, a positive magnitude for ,Ho can still arise despite all reactions within the subset being characterized by negative enthalpy changes: designation of the reaction as being entropy driven is thus equivocal. An experimenter must always bear in mind the fact that any mechanistic interpretation of the magnitudes of thermodynamic parameters refers to the reaction model rather than the experimental system For the same reason there is little point in subjecting the temperature dependence of rate constants for protein interactions to transition-state analysis. If comparisons with reported values of standard enthalpy and entropy of activation are needed, they are readily calculated from the empirical Arrhenius parameters. Copyright © 2006 John Wiley & Sons, Ltd. [source] Decomposition of monochlorobiphenyl isomers in supercritical water in the presence of methanolAICHE JOURNAL, Issue 7 2004Gheorghe Anitescu Abstract Comprehensive studies of monochlorobiphenyl (MCB) decomposition in supercritical water in the presence of methanol and other cosolvents, both with and without oxygen, are being conducted to understand the reaction kinetics and pathways of individual PCB isomers and to determine the structure,reactivity relationships. In the present study the disappearance rate of MCBs, delivered in an isothermal plug-flow tubular reactor as methanolic solutions, is investigated at 25 MPa and temperatures of 673, 723, and 773 K. Experiments are conducted at nominal MCB feed concentrations of 1,100 ,mol/L (reaction conditions) using MCB/MeOH and H2O2/H2O solutions (1,3 g/L and 0,10 wt. %, respectively). Molar conversions of these isomers vary from 3% (2-CB, 773 K, 2 s) to 30% (4-CB, 773 K, 46 s) without oxygen (SCWT) and from 1% (2-CB, 673 K, 3.8 s) to 97% (4-CB, 773 K, 24.5 s) with oxygen (SCWO). For SCWT the overall conversion follows apparent first order, whereas for SCWO the conversion is second order. The regressed data lead to Arrhenius parameters of frequency factor and activation energy with values of 1020.5,1021.3 s,1 and 320,331 kJ/mol for SCWT and 1024.1,1024.8 s,1 (mol/L),1 and 281,292 kJ/mol for SCWO, respectively. The reactivity of the MCB isomers increases in the order 2-MCB < 3-MCB < 4-MCB. The positively identified reaction products by GC-MSD and GC-FID/ECD/TCD analyses are mainly biphenyl, open-ring biphenyl compounds such as acetophenone and benzaldehydes, and mineral products (CO, CO2, and HCl). More studies are in progress regarding the role of the second solvent on reaction rates and reaction mechanisms and pathways. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1536,1544, 2004 [source] Pulsed laser polymerization study of the propagation kinetics of acrylamide in waterJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2005Shane A. Seabrook Abstract Pulsed laser polymerization was used in conjunction with aqueous-phase size exclusion chromatography with multi-angle laser light scattering detection to determine the propagation rate coefficient (kp) for the water-soluble monomer acrylamide. The influence of the monomer concentration was investigated from 0.3 to 2.8 M, and kp decreased with increasing monomer concentration. These data and data for acrylic acid in water were consistent with this decrease being caused by the depletion of the monomer concentration by dimer formation in water. Two photoinitiators, uranyl nitrate and 2,2,-azobis(2-amidinopropane) (V-50), were used; kp was dependent on their concentrations. The concentration dependence of kp was ascribed to a combination of solvent effects arising from association (thermodynamic effects) and changes in the free energy of activation (effects of the solvent on the structure of the reactant and transition state). Arrhenius parameters for kp (M,1 s,1) = 107.2 exp(,13.4 kJ mol,1/RT) and kp (M,1 s,1) = 107.1 exp(,12.9 kJ mol,1/RT) were obtained for 0.002 M uranyl nitrate and V-50, respectively, with a monomer concentration of 0.32 M. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1357,1368, 2005 [source] | ||||||||||