First-order reaction mechanisms

Mass-spectrometric research on silane decomposition kinetics has been performed for flowing [298, 302-306] and static discharges [197, 307]. In a dc discharge of silane it is found that the reaction rate for the depletion of silane is a linear function of the dc current in the discharge, which allows one to determine a first-order reaction mechanism in electron density and temperature [302, 304]. For an RF discharge, similar results are found [303, 305]. Also, the depletion and production rates were found to be temperature-dependent [306]. Further, the depletion of silane and the production of disilane and trisilane are found to depend on the dwell time in the reactor [298]. The increase of di- and trisilane concentration at short dwell times (<0.5 s) corresponds to the decrease of silane concentration. At long dwell times, the decomposition of di- and trisilane produces... 

Figure 7.5 A plot of the variation in the concentration of the reaction intermediate, [B], with time in a two sequential first-order reaction mechanism...

Of the wide range of these types of processes, this study focuses mainly on three first- or pseudo-first-order reaction mechanisms (see reaction scheme (6.IV)) catalytic, EC, and CE processes which are the most analyzed in the Electrochemistry literature. 

Figure 19.24 shows the TGA measurements of a PA6 sample in nitrogen (represented as symbols) at five heating rates, i.e., 1, 2, 5,10 (also shown in Figure 19.4), and 20K/min, along with the best fits (represented as lines) obtained using a first-order reaction mechanism, i.e.,... 

In Table 5.4 the kj values show a definite trend with time while the k2 values show small variations with no definite trend. Therefore, the first-order reaction mechanism does not adequately describe the experimental kinetic data. 

It has been shown by Chavarie and Grace (15) that the decomposition of ozone in a fluidized-bed is best described by Kunii and Levenspiel s model (16) but that the Orcutt and Davidson models (17) gave the next best approximation for the overall behaviour and are easier to use and were chosen for the simulation. They suppose a uniform bubble size distribution with mass transfer accomplished by percolation and diffusion. The difference between the two models is the presumption of the type of gas flow in the emulsion phase piston flow, PF, for one model and a perfectly mixed, PM, emulsion phase for the other model. The two models give the following expressions at the surface of the fluidized bed for first-order reaction mechanism ... 

A complete pathway for the mineralization of 4-chlorophenol can be described by the hydroxylation reaction through dechlorination, ring cleavage, and mineralization. Reaction kinetics of the 4-chlorophenol and its intermediates can be reasonably well approximated by using a complex parallel and consecutive first-order reaction mechanism. 

Thermal decomposition of Si-H, Sl-C and N-H bonds in PP-HMCTS proceeds by a first order reaction mechanism. 

SO that a first-order reaction mechanism can be assumed and a linear dependence of the kinetic rate upon substrate concentration, with a slope equal to RmaxIKm, is observed. 

The activation energies and reaction order for the decomposition reaction RCrO - RCrOj + jO2 have been determined by Doyle and Pryde (1976) and Roy et al. (1978). As these calculations are strongly dependent on the experimental and calculation methods, the significantly different activation energies obtained by the two groups cannot be directly compared. Nevertheless, it may be noted that both isothermal measurements (Doyle and Pryde, 1976) and nonisothermal measurements combined with another computational procedure (Roy et al., 1978) support a first-order reaction mechanism for LaCrO. ... 

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