Mecanismos de cinética química detalhada são rotineiramente usados para descrever, a nível molecular, a transformação de reagentes em produtos de combustão, que ocorre através de muitas etapas elementares. Seu uso em modelos computacionais para simular processos de combustão pode gerar informações para melhorar o processo de uso do combustível e o desempenho do processo de combustão, e para quantificar as emissões a partir deste processo. Assim, para descrever um processo de oxidação, o esforço computacional se torna muito grande, exigindo simplificações do mecanismo. O desenvolvimento de mecanismos de cinética química reduzida para processos de combustão visa reduzir a esforço computacional na análise numérica de chamas. Os modelos cinéticos reduzidos podem substituir as equações diferenciais das espécies intermediárias, que são consideradas estarem em estado estacionário, através de relações algébricas. Desta forma, este trabalho desenvolve um método para reduzir a cinética química para a combustão do hidrogênio, monóxido de carbono, e hidrocarbonetos C1- C7, utilizando os pressupostos de estado estacionário. Um mecanismo cinético detalhado do processo de combustão de 439 reações elementares foi estudado e reduzido a mecanismos com, no máximo, 9 passos globais. Comparações de dados experimentais com simulações do perfil de fração de massa de CO2 e H2O, produzidos utilizando o mecanismo cinético reduzido do metano, propano e n-heptano demonstram boa concordância, validando estes mecanismos e, consequentemente, aumentando a confiabilidade dos demais mecanismos estudados. / Detailed chemical kinetic mechanisms are routinely used to describe, at the molecular level, the transformation of reactants to products of combustion, which occurs via many elementary steps. Its use in computer models to simulate combustion processes can generate information to improve the fuel quality and performance of the combustion process, and to quantify the emissions from this process. Thus, to describe a process of oxidation, the computational effort becomes very large, requiring simplifications of the reaction mechanism. The development of reduced kinetic mechanisms for combustion processes aims to reduce the computational effort necessary for the numerical analysis. The reduced models can replace the differential equations of the intermediate species, which are considered to be in steady state, through algebraic relationships. In this way, this work develops a method for reducing the kinetics of combustion for hydrogen, carbon monoxide and hydrocarbons C1-C7, using assumptions of steady-state. A detailed kinetic mechanism containing 439 elementary reactions was analysed and reduced mechanisms with up to 10 steps were developed. Comparisons between experiment and simulations for the reduced kinetic mechanism of methane and propane, show good agreement, validating these mechanisms, and consequently, increasing the reliability of the others mechanisms studied.

The temperature dependence of the reactions of halogen atoms Cl and Br with SiH4 and (CH3)3SiH have been investigated with the flash photolysis-resonance fluorescence technique. CCI4 and CH2Br2 were used as precursors to produce Cl and Br atoms, respectively. Experiments gave {k(Cl + SiH4) (295 - 472 K)} = (1.56 +0.11) x 10-1 exp[(2.0 + 0.2) kJ mol'/RT] cm3 s4, {k(Br + SiH4)(295 - 575 K)} = (9.0 + 1.5) x 10-" exp[-(17.0 + 0.6) Id mol'/RT] cm3 s', {k(Cl + (CH3)3SiH)(295 - 468 K)} = (1.24 0.35) x 104 exp[(1.3 + 0.8) Id mol4/RT] cm3 s', and {k(Br + (CH3)3SiH)(295 - 456 K)} = (7.6 + 3.3) x 1010 exp[-(28.4 + 1.3) Id mol'/RT] cm3 s'. The results were compared with values from earlier work.

The kinetics of the Cu⁺⁺ catalysed reduction of dichromate by hydrogen in aqueous perchlorate solutions were investigated between 160° and 200°C. A significant dependence of rates on Cr[superscript](VI) was observed. The mechanism proposed to account for the kinetics gave rise to a rate law of the form [formula omitted] where the rate constant for the hydrogen activation step, k₁, is given by [formula omitted]. The rate constant ratios k₋₁/k₂ and k₋₁/k₃ are believed to be temperature independent in the temperature range under consideration, and have approximate values of 0.38 and 0.02 respectively. As a consequence of these studies a similar mechanism was proposed for the Cu⁺⁺ catalysed hydrogen-oxygen recombination reaction investigated by McDuffie and co-workers. According to this mechanism an apparent discrepancy between the observations of Halpern et al and those of the former workers can be explained. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

The kinetics of the reduction of silver amine complexes in aqueous solutions were investigated and found to be second order overall, the rate being proportional to silver complex and hydrogen concentrations. These systems were studied under conditions of essentially complete complexing and therefore the rates were independent of amine concentration. The rates were also shown to be independent of amine perchlorate concentration and thus of pH within a limited range. Enthalpies and entropies of activation were determined for each system and an attempt was made to correlate kinetic data with information on complex stability constants and amine basicities. The most prominent trend in the results was the inverse dependence of rate on complex stability constant. Two mechanisms are proposed both involving heterolytic cleavage of the hydrogen molecule. In the first mechanism, the proton released in the rate determining step is taken up by the basic ligand directly. In the second mechanism, a water molecule replaces the amine ligand and acts as the proton acceptor. The strength of the silver-ligand bond and the difficulty of ligand replacement by water account for the inverse dependence of rate on complex stability for each mechanism respectively. Arguments are presented to support both mechanisms. In general dibasic amine complexes activated hydrogen more readily and displayed a more negative entropy of activation than do the monoamine complexes. These observations are attributed to the presence of a free basic group in the ligand aiding the cleavage of the hydrogen molecule in the rate determining step. The proximity of the second basic group to the central silver atom also appears to be important. These effects and the possible role of the free basic group in the ligand are discussed. / Science, Faculty of / Chemistry, Department of / Graduate

D.Ed. (Didactics) / This study focused on the misconceptions which exist among standerd ten pupils in the field of chemical equilibrium and the rate of chemical reactions. Although the teacher Is confident that meaningful teaching occurs In the classroom situation, misconceptions do materialise frequently. Several factors concerning the pupil, the teacher as well as the subject content Itself were Investigated. The main objective of this study Is to Investigate the nature and extent of the misconceptions regarding the rate of chemical reactions and the chemical equilibrium experienced by standard ten pupils. Following this, pupils are exposed to a computer program which has been complied to eliminate the misconceptions regarding these two themes...

The kinetics of the gas-phase reactions of chlorine atoms with fluoromethane (CH3F) and fluoromethane-d3(CD3F) were tested experimentally. The relative rate method was applied by using CH4 as the reference compound for fluoromethane (CH3F) and CH4 and CH3F as the reference compound for fluoromethane-d3(CD3F). The rate constants for H-abstraction from CH3F and D-abstraction from CD3F were measured at room temperature and a total pressure of 920 Torr using Ar as a diluent. The rate constants are described by the expressions: kH= (3.50±0.52) x 10-13 cm3 molecule-1 s-1 and kD=(5.0±0.51) x 10-14 cm3 molecule-1 s-1. The kinetic isotope effect, equal to the ratio kH/kD, was found to be 7.0±1.2 at room temperature.

The reaction of 1-(diphenylphosphino)-2-(diphenylphosphito)benzene (PP*) and Os3(CO)10(ACN) has been investigated. A combined experimental and computational study on the isomerization of 1,2-Os3(CO)10[μ-1,2-Ph2P(C6H4)P(OPh)2] (A) and 1,1-Os3(CO)10[μ-1,2-Ph2P(C6H4)P(OPh)2] (B) and reversible ortho-metalation exhibited by the triosmium cluster B are reported. The subsequent conversion of cluster B to the hydrido cluster HOs3(CO)9[μ-1,2-PhP(C6H4-η1)C6H4P(OPh)2] (E) and the benzyne-substituted cluster HOs3(CO)8(µ3-C6H4)[μ-1,2-PhP(C6H4)P(OPh)2] (N) has been established. All of these new clusters have been isolated and fully characterized in solution by IR and NMR spectroscopy; in addition, X-ray diffraction analyses have been performed on the clusters A, B, J, and N. The ortho-metalation reaction that gives cluster E is shown to be reversible, and the mechanism has been probed using selectively deuterated PP* isotopomers. Kinetic and thermodynamic isotope data, in conjunction with DFT calculations, are presented that support the existence of an intermediate unsaturated cluster in the ortho-metalation reaction. Due to interest in the coordination chemistry of formamidines, the non-symmetric amidine ligands PhNC(Me)NHPri, PhNC(Et)NHPri, and (2,4,6-Me3C6H2)NC(Me)NHPri, have been synthesized, and their reaction with Os3(CO)10(MeCN)2 has been investigated. Of the twelve new clusters prepared in section, seven have been structurally characterized by X-ray crystallography.

Future thrusts for gasoline engine development can be broadly summarized into two categories: (i) efficiency improvements in conventional spark ignition engines, and (ii) development of advance compression ignition (ACI) concepts. Efficiency improvements in conventional spark ignition engines requires downsizing (and turbocharging) which may be achieved by using high octane gasolines, whereas, low octane gasolines fuels are anticipated for ACI concepts. The current work provides the essential combustion kinetic data, targeting both thrusts, that is needed to develop high fidelity gasoline surrogate mechanisms and surrogate complexity guidelines. Ignition delay times of a wide range of certified gasolines and surrogates are reported here. These measurements were performed in shock tubes and rapid compression machines over a wide range of experimental conditions (650 – 1250 K, 10 – 40 bar) relevant to internal combustion engines. Using the measured the data and chemical kinetic analyses, the surrogate complexity requirements for these gasolines in homogeneous environments are specified. For the discussions presented here, gasolines are classified into three categories: (i) Low octane gasolines including Saudi Aramco’s light naphtha fuel (anti-knock index, AKI = (RON + MON)/2 = 64; Sensitivity (S) = RON – MON = 1), certified FACE (Fuels for Advanced Combustion Engines) gasoline I and J (AKI ~ 70, S = 0.7 and 3 respectively), and their Primary Reference Fuels (PRF, mixtures of n-heptane and iso-octane) and multi-component surrogates. (ii) Mid octane gasolines including FACE A and C (AKI ~ 84, S ~ 0 and 1 respectively) and their PRF surrogates. Laser absorption measurements of intermediate and product species formed during gasoline/surrogate oxidation are also reported. (iii) A wide range of n-heptane/iso-octane/toluene (TPRF) blends to adequately represent the octane and sensitivity requirements of high octane gasolines including FACE gasoline F and G (AKI ~ 91, S = 5.6 and 11 respectively) and certified Haltermann (AKI ~ 87, S = 7.6) and Coryton (AKI ~ 92, S = 10.9) gasolines. To assess conditions where shock tubes may not be ideal devices for ignition delay measurements, this work also presents a detailed discussion on shock tube pre-ignition affected ignition data and the ignition regimes in homogeneous environments. The shock tube studies on pre-ignition and associated bulk ignition advance may help engines research community understand and control super-knock events.

The purpose of this thesis was to determine the kinetics and stoichiometry for the aquation of the pentaaquomonobromonmethylchromium(III) complex. The complex was prepared by the reduction of dibromomethane by chromium(II). The products of aquation, in the absence of oxygen, were found to be hexaaquachromium(III), methanol, and bromide. The balanced net ionic reaction can be written: 2H2O + (H2O)5CrCH2Br2+ → (H2O)6Cr3+ + CH3OH + Br-

Gas phase kinetics and thermochemistry of several halogenated species relevant to atmospheric, combustion and plasma chemistry were studied using experimental and ab initio theoretical techniques.