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Item Kinetics of the Reaction Between 2,4-Dinitrophenol and Tri-n-octylamine in Chlorobenzene Solution Diffusion and other Rate-limiting Factors(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Caldin, Edward F.; Tortschanoff, KarlThe kinetics of the reaction between 2,4-dinitrophenol and tri-n-octylamine in chlorobenzene solution have been investigated by a microwave temperature-jump technique. The rate constant is about 30 times smaller than the value calculated from the Smoluchowski treatment for a diffusion-controlled reaction. The activation enthalpy is slightly negative (ΔH[graphic omitted]=–6.7 ± 2 kJ mol–1 or –1.6 ± 0.5 kcal mol–1). This is strong evidence against a one-step mechanism. A three-step mechanism accommodates the results. For this mechanism the significant fact about ΔH[graphic omitted] is that it is lower than the viscosity-controlled value, rather than the fact that it is negative.Item Second Limit of Hydrogen-I-Oxygen Mixtures: the Reaction H+HO2(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Baldwin, Roy R.; Fuller, Margaret E.; Hillman, John S.Measurements of the second limit of H2+ O2 mixtures at very low O2 concentrations have shown that the results at 500°C cannot be interpreted on the assumption that the only reaction between H atoms and HO2 radicals is the quadratic branching reaction H + HO2→2OH (8) whereas a precise interpretation is possible by introducing the additional reaction H + HO2→H2+ O2, (8a) with the ratio k8a/k8= 0.17. An alternative explanation in terms of destruction of H atoms at the surface has been eliminated by measurement of the first limit. Comparison of the above estimate at 500°C with the mean of k8a/(k8+k8b)≈1, obtained at 20°C suggests that E8–E8a≈1725 cal mol–1; if E8a= 0, (k8+k8b)= 3.1 × 1011 exp(–1725 cal mol–1/RT) dm3 mol–1 s–1. The present work does not distinguish between (8) and the kinetically equivalent reaction H + HO2→H2O + O (8b) but other workers have suggested that k8b/k8≈0.1. A higher activation energy and higher preexponential factor for the equivalent reaction, involving O—O bond fission rather than H abstraction, has also been found in the reaction H + H2O2.Item Rational Definition of Rate of Reaction: General Method of Expressing Ratc Which Leads to No Anomalies in Systems of Changing Volume(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Hutchison, J.; Lehrle, R. S.; Robb, J. C.; Suggate, J. R.The conventional way of expressing rate of reaction in terms of rate of change of concentration (e.g. –d[A]/dt) is shown to be inappropriate for systems in which any volume change accompanies the conversion. Thus for such liquid phase reactions, with or without inert solvent, it is demonstrated that the rate of decrease of reactant concentration is not equal to the rate of increase of product concentration, that the apparent external order of reaction depends on whether the rate is expressed in terms of reactant or product, and that the apparent internal order of reaction can not reflect the molecularity of the reaction process. A revised expression for rate of reaction is proposed; this defines the rate at any time as the product of the time derivative of the number of moles of a reaction component and the reciprocal volume of the system at that time, e.g.–(1/Vt)(dA/dt)t. The above anomalies do not arise when rates are expressed in this way; it is therefore recommended that this revised definition of rate be generally employed in all kinetic studies.Item Mechanistic Conclusions from the Curvature of Solvent Isotope Effects(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Albery, W. J.; Davies, M. H.The variation of kx/k0 with x the atom fraction of D in H2O/D2O mixtures is generally curved. Models of the transition state to fit this curve are described by fractionation factor theory. Nine general conclusions are drawn about the relationship between the model of the transition state and degree of curvature. The handling of data is much simplified by using a binomial expansion about x=½. It is shown how the different models of the transition states which give the same curvature and overall solvent isotope effect may be represented by simple diagrams both for a single transition state and for reactions proceeding through two parallel or consecutive transition states. Some data for the solvolysis of t-butyl chloride are used to exemplify the approach.Item Thermal Decomposition of Ethyl, Isopropyl and t-Butyl Fluorides in the Gas Phase(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (11), 1972) Dastoor, P. N.; Emovon, E. U.Ethyl, isopropyl and t-butyl fluorides decompose in a flow system into hydrogen fluoride and the corresponding olefin by a predominantly molecular mechanism. The first order rate constants are given by the Arrhenius equations: ethyl fluoride (520–600°C) : k/s–1= 1012.16±0.04exp–59 200±2000/RT, isopropyl fluoride(445–522°C) : k/s–1= 1011.83±0.02 exp–53 900±800/RT, t-butyl fluoride (329–370°C) : k/s–1= 1013.96±0.01 exp–50 400±900/RT.Item Kinetics of the Reactions of Oxygen Atoms and Nitrogen Atoms with Sulphur Trioxide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (11), 1972) Jacob, Adir; Winkler, C. A.The reaction of O atoms with SO3 yields SO2 and O2 as stable products, with a white metastable solid that condenses at –10°C (thought to be SO4) as a probable intermediate. The overall rate constants are 5 × 10–17, 7 × 10–17 and 9 × 10–17 cm3 molecule–1 s–1 at 300, 413 and 500 K, respectively. The activation energy is about 1 kcal mol–1, with a correspondingly low frequency factor of 3 × 10–15 cm3 molecule–1 s–1. The reaction of N atoms with SO3 yields SO2 as a main product, with an overall rate constant of about 5 × 10–16 cm3 molecule–1 s–1 at 300 K.