Interpretation of kinetic observations

As previously emphasized, the positive identification of the specific entities that participate in the rate-limiting step of a catalytic reaction is a matter of considerable difficulty. Aspects of this problem have been discussed by Knozinger et al. 67) and by Webb (66). Thus, the interpretation of kinetic observations for heterogeneous processes must include consideration of the following possibilities. (It is not intended to imply, however, that every heterogeneous reaction necessarily includes each effect mentioned.)... 

Measured rates of reactions may include contributions from reverse processes which must be investigated and allowed for in the interpretation of kinetic observations (see Chapter 12). 

In the chemistry laboratory, these systems ate most often encountered with the gases Hj or CO reacting with substrate and possibly a catalyst in the liquid phase. For the mechanistic interpretation of kinetic observations, an important factor is the rate of mass transfer of the gas to the liquid phase. The rate of gas absorption into the liquid is typically represented as a first-order process, driven by the difference between the saturated gas concentration [G(o]f and the concentration at any time [G(ol, as given by... 

The decomposition kinetics of mercury fulminate [725] are significantly influenced by ageing, pre-irradiation and crushing these additional features of reaction facilitated interpretation of the observations and, in particular, the role of intergranular material in salt breakdown. Following a slow evolution of gas ( 0.1%) during the induction period, the accelerator process for the fresh salt obeyed the exponential law [eqn. (8)] when a < 0.35. The induction period for the aged salt was somewhat shorter and here the acceleratory process obeyed the cube law [eqn. (2), n = 3] and E = 113 kj mole-1. 

Detailed interpretation of kinetic test data collected for environmental purposes has allowed criteria for ground and surface water geochemical exploration to be selected. Parameters predicted from kinetic testing to be anomalous in both ground and surface waters were observed to occur reflecting the presence of both molybdenum mineralization and natural acid rock drainage. Kinetic testing is very expensive and careful use of the acquired... 

It has not been possible so far to construct a complete interpretation of these observations in terms of a mechanism and a corresponding kinetic scheme. However, a few conclusions appear to be fairly obvious. 

Abstract The theoretical framework needed for interpretation of kinetic isotope effects on unimolecular reactions is reviewed. Application to the satisfactory rationalization of the theoretically puzzling mass independent isotope effect observed for oxygen isotope fractionation in extraterrestrial samples is described. 

The interpretation of kinetic data begins with a hypothetical sequence of ele mentary reaction steps, each characterized by two microscopic rate constants, one for the forward and one for the reverse reaction. From this proposed mechanism a rate equation is derived, predicting the dependence of the observed reaction rate on concentrations and on microscopic rate constants, and its form is tested against the observations. If the form of the rate equation meets the test of experiment, it may be possible to derive from the data numerical values for the microscopic rate constants of the proposed elementary reaction steps. While inconsistency is clear grounds for modifying or rejecting a mechanistic hypothesis, agreement does not prove the proposed mechanism correct. 

Most of the kinetic results so far obtained upon oxygen exchange are summarized in Figs. 3 to 6, which also show the kinetics of the equilibration reaction plotted to the same scale. Before attempting an interpretation of these observations, it is desirable to consider first the nature and extent of the oxide surface and the adsorption of oxygen thereon and also to review briefly other experimental evidence regarding the interaction between gas and surface. 

A general form of the characteristic equation in combination with a steady-state kinetic equation will provide additional possibilities for the interpretation of the observed kinetic relationships. 

The early kinetic studies on glutathione reductase did not include investigation of product inhibition, so vital to a proper interpretation of kinetic data in the elucidation of the mechanism 247, 248). In the one case where product inhibition patterns were observed, they were not interpreted by more recent kinetic theory 40). Subsequent kinetic analyses see below), in which product inhibition patterns have been obtained, were either completed prior to the discovery of the EH2-NADPH complex... 

The closely related monomer, sym-trioxan, is a crystalline trimer of formaldehyde, and again polymerizable by cationic means [151, 160]. However, considerable induction periods are observed in its solution polymerization, and the interpretation of kinetic data is additionally complicated by the formation of equilibrium amounts of monomeric formaldehyde as well as polyoxymethylene. 

Proof for single-electron transfer in reactions of allyl- and crotylmagnesium bromide with benzophenone had been reported a few years before, in 1988, based on measurements of carbonyl carbon kinetic isotope effects (which were nonexistent) and substituent effect techniques [65]. Doubt about the correct interpretation of the observed phenomenon was discussed earlier in this chapter (see p. 237 [13]). 

Polarization behavior relates to the kinetics of electrochemical processes. Study of the phenomenon requires techniques for simultaneously measuring electrode potentials and current densities and developing empirical and theoretical relationships between the two. Before examining some of the simple theories, experimental techniques, and interpretations of the observed relationships, it is useful to characterize the polarization behavior of several of the important electrochemical reactions involved in corrosion processes. 

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