Reaction, exothermic rate, definition

This definition excludes those exothermic reactions which shown and increase in rate with time (like explosions caused by the rapidly rising temperature. 

Catalyst supports such as silica and alumina have low thermal conductivities so that temperature gradients within catalyst particles are likely in all but the finely ground powders used for infrinsic kinetic studies. There may also be a film resisfance fo heaf fransfer af fhe exfemal surface of the catalyst. Thus the internal temperatures in a catalyst pellet may be substantially different than the bulk gas temperature. The definition of the effectiveness factor, Equation 10.23, is unchanged, but an exothermic reaction can have reaction rates inside the pellet that are higher than would be predicted using the bulk gas temperature. In the absence of a diffusion limitation, rj > 1 would be expected for an exothermic reaction. (The case > 1 is also possible for some isothermal reactions with weird kinetics.) Mass transfer limitations may have a larger... 

If the temperature of ihe sample is taken as the temperature measured by a thermocouple located just above or below the sample container, then the true sample temperature will either lead or lag behind the furnace temperature. The magnitude of this difference depends on the nature of the reaction (whether it is endothermic or exothermic), the heating rate, the sample thermal conductivity, the geometry of the sample holder, and so on. This effect is illustrated by the curves for the sample and thermowell temperatures of CaC204 H20, as shown in Figure 2.29. There are definite inflections at... 

The relative importance of vibrational and translational energy in promoting chemical reactions is of both theoretical and practical interest. In reactions of diatomic molecules with atoms it has been substantiated both experimentally and theoretically that for endothermic reactions vibrational energy is more important, while for exothermic reactions the opposite is true. For polyatomic molecules, however, there is insufficient experimental and theoretical evidence to draw conclusions. The major work on laser-excited polyatomic reactions has involved the vibrational excitation of ozone in its exothermic reaction with nitric oxide. Although the vibrational energy increased the reaction rate, comparison with statistical models and the temperature dependence of the thermal reaction indicate about equal importance for vibrational and translational energy. On the other hand, a molecular beam study of the temperature dependence of the reaction of potassium with sulfur hexafluoride" has shown a definite preference for vibrational energy of the SF. ... 

Quantitative description of the induction period by a definite time interval, or induction time, ti, is aided by the precise time origin provided by a shock wave. The specification of the end of the induction period is conceptually more difficult, however, and no universally preferred criterion has been found. One approach, which is appealing when one wants to emphasize the induction time as a determinant of the time scale of the main reaction, is to reckon by the occurrence of an inflection or maximum in such quantities as the rate of exothermic expansion or in the formation of some product, byproduct (such as chemiluminescent photons), or intermediate. This approach suffers conceptually from the fact that such phenomena are generally not quite simultaneous with each other, even though the differences are minor in comparison with the major effects of varying gas density, composition and temperature. 

The Marcus equation predicts that, for given values of H21 and A, og(ket) depends quadratically on (4G° +A). Because A is positive by definition, this means that the reaction will be slow if it is strongly exothermic (AG°-C —A), as well as if it is endothermic (AG° > 0). The rate should be maximal when AG°=—A. The prediction that making a reaction more exothermic can decrease its rate was unexpected when Marcus advanced it [91], and was not verified experimentally for many years [93-95]. The kinetics of electron transfer between reactants in solution can be complicated by formation of intermediate complexes and can be limited by the rate of diffusion of the reactants [96, 97]. 

Carbamic acids (RNHCOOH) appear to be fairly strong acids with estimated pK values in the neighborhood of 6.8 (174).It is also known that the carbamate reaction is a strongly exothermic one, having a heat of the order of 20,000 cal./mole (130, 174). Apparently the reaction is limited to aliphatic amines at any rate it does not take place with the NH group of histidine (176). In accordance with these considerations the expression for the equilibrium between an amine (RNHj) and carbon dioxide may be formulated on the basis of simple mass law considerations. To do so, we introduce the following definitions and equations ... 

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