Kinetic regularities

Lekishvili N.G., Katsitadze M.G., Nakaidze L.I., Khananashvili L.M. Some Kinetically Regularities of Polymerization Condensation Reaction of Organocyclosilazanes with Spacial Groups at Silicon Atoms with Aromatic Dihydroxy compounds. Bulletin of the Academy of Sciences of Georgia. Series of Chemistry. 152, 3 529-531 (1995) (Rus.). 

The determination of the kinetic regularities for different systems is important in the first turn for understandina of the process of the networks formation and for the study of sol and gel properties. On the other hand, the solution of the kinetic problem is of the great importance from the viewpoint of the further development of the general theory of macromole-cular reactions. 

These conceptions have given impetus to the development of two trends that must complement each other studies of the kinetic regularities of elementary acts and construction of the kinetic theory for complex reactions. 

As early as in 1934 Semenov said that "the classification of reactions by their kinetic regularities, even if it is much more complicated than the Mendeleev classification of elements by their properties (the periodic law), seems nevertheless to be possible [32, p. 538]. 

To repeat the route of chemistry in the kinetic aspect , that was the formulation of the problem. To our mind, however, in the 1930s "the rational classification principle , whose appearance was predicted by Semenov, could not be realized. The possibility of solving this problem appeared only in recent times in terms of the concepts of the graph theory and the qualitative theory of differential equations. The analysis of the effect of the mechanism structure on the kinetic regularities of catalytic reactions is one of the connecting subjects in the present study. 

Note that these problems, unlike those associated with the elucidation of the kinetic regularities in elementary acts, is not very popular, in particular among kinetic chemists. What are the reasons It is likely that they are historical and psychological. One must hope that in the near future the situation will change since to understand the way of "assembling a com-... 

At first it was believed that the main factor responsible for the kinetic regularities is the displacement or the "competition of reaction mixture components for the catalyst surface sites. An additional assumption was made concerning the high rate of the adsorption and desorption steps compared with the chemical transformations proper. 

V.A. Kritsman, Structural Kinetic Regularities, Nauka, Moscow, 1974 (in Russian). 

OBSERVED KINETIC REGULARITIES AND CHARACTERISTICS OF DETAILED MECHANISMS... 

Nevertheless even now it is possible to apply the qualitative investigation of kinetic models corresponding to simple model mechanisms, not only for a description of the established experimental kinetic curves, but also for the prediction of kinetic regularities in the parametric region that has not been examined by experiment [165]. 

Of special attention is the work [24] in which kinetic regularities of ethane oxidation by oxygen performed at 600-630 °C in a flow reactor in the low transformation zone were successfully and semi-quantitatively explained by the radical-chain mechanism with H202 as a source of two active particles ... 

Based on kinetic regularities following from the type of these curves, one may make an important conclusion that for every particular condition, the totality of reaction products will correspond to a constant value of the actor consumption or, in accordance with stoichiometry (scheme 3) of the inducer and the assumption (e.g. postulation) of its complete consumption, the following expression becomes valid ... 

The kinetics of consecutive, consecutive-parallel and parallel reactions of any complexity is discussed in classical monographs on chemical kinetics [1-3,11] and are not considered in the current monograph. The scope of kinetic regularities of these complex reactions mentioned will be minimally required for a clear understanding of their differences from kinetics of conjugated reactions. 

In fact, there are examples of chemical reaction in catalysis, which proceed on membranes not dividing the reaction zone into zones. They behave in the system as normal catalysts, e.g. obeying kinetic regularities of heterogeneous catalytic systems. 

Further experimental studies of kinetic regularities have shown that the totality of elementary stages currently presented is the most probable and adequate describes thermolysis of gaseous hydrogen peroxide [15,16]. Free radical decay in the gas phase on the reactor walls is more probable than the chain termination in the volume and, therefore, this circumstance should be reflected in the scheme. This was attempted in an article [17], according to which chain termination occurs by the following mechanism ... 

The bulk of experimental data makes possible the detection of several nontrivial kinetic regularities, among which the synchronized curves shown in Figures 4.14 1.17 are of special... 

Conjugated dehydrogenation of cyclopentane to cyclopentadiene passes through an intermediate formation of cyclopentene, and kinetic regularities of this reaction are identical to those for cyclohexane ... 

The scope of the experimental data allowed the determination of several kinetic regularities, among which the synchronized curves (Figure 5.2) are of special interest which demonstrate the induction effect of the primary reaction (hydrogen peroxide dissociation) on the secondary (inducible) reaction of CH4 hydroxylation. 

Thus, current kinetic regularities correspond to the suggested mechanism, according to which OH and H02 radicals are the main active sites in the CH4—H202—H20 system. 

Epoxidation and hydroxylation activity of iron(III) perfluorotetraphenylporphyrin biomimic was studied in a quartz flow reactor with the reaction zone 1.7 cm long and 1.8 cm in diameter. Kinetic regularities of monooxygenase reaction were studied at 180-320 °C and molar ratios C3H6 H202 equal 1 0.5 and 1 2. 

The catalyst indicated extremely high resistance to the effects of oxidants and their intermediates and relatively high temperature, e.g. it preserves the ability to epoxidize during the whole time of the biomimic tests. Owing to the mentioned properties of the mimic, kinetic regularities of current monooxygenase reaction were studied in a broad range of reaction parameters with reproducible results. 

The kinetic regularities observed lead to consideration of the hydroxylation mechanism in the context of modem ideas about enzymatic catalysis mechanism. 

The basic kinetic regularities of film growth must be considered to build the film deposition kinetic mechanism. In the case of Zr02 film growth from... 

I.C. Analysis of Kinetic Regularities of the System under Study... 

Since the surface properties of the colloid have a strong influence on the photoreduction kinetics, it seemed interesting to elucidate the effect of the added surface-active substances on the kinetic regularities of the reactions photosensitized by semiconductor colloid. The surfactant molecules are known to concentrate near the surface of the colloidal particle, so they may affect strongly the kinetics of photocatalytic reactions proceeding at the particles surface [52,53]. Fig. 2.30 presents the temperature dependencies of the initial rate of the MV photoreduction over colloidal CdS prepared at the excess of the sulfide ions. These dependencies were obtained at the addition of different amounts of PAA. One may see that both the initial rate and the observed activation energy of the methylviologen photoreduction do not depend, within the experimental error, on the concentration of... 

The kinetic regularities of heterogeneous defoaming, i.e. the acceleration of foam breakdown with the decrease in hydrocarbon molecular weight (respectively, the decrease in hydrocarbon surface tension and the increase in the contact angle between the meniscus and the substrate) and with the increase in both foam expansion ratio and reduced pressure, indicate that foam breakdown can occur due to the lowered stability of film borders at their contact with the substrate (worsened wetting). The fact that the foam situated between the cuvette wall and the capillary decayed at a considerably slower rate is in benefit to this statement. 

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