Kinetic path

Figure 5 Free energy surface at l l(Fig. 5a) [22, 24, 28] and 1 3 (Fig. 5b) [23, 24, 33] stoichiometries in the vicinity of disordered state ( f=0.0) at T—. 7Q and 1.6, respectively. The solid line in left-hand (right-hand) figure indicates the kinetic path evolving towards the L q LI2 ordered phase when the system is quenched from T—2.5 (3.0) down to 1.70 (1.60), while the broken lines are devolving towards disordered phase. The open arrows on the contour surface designate the direction of the decrease of free energy, and the arrows on the kinetic path indicate the direction of time evolution or devolution.

Kemkes256 assumes that the overall order relative to the esterification of terephthalic acid by 1,2-ethanediol in oligo(l,2-ethanediyl terephthalate) is two no mechanism has however been suggested. Mares257 considers that during the esterification of terephthalic acid with 1,2-ethanediol, two parallel kinetic paths take place, one corresponding to a reaction catalyzed by non-dissociated add and the other to a non-catalyzed process. In fact, Mares257 is reserved about the existence of protonic catalysis. Some other orders were found for the system terephthalic atid/l,2-ethanediol 0 (overall)318 2 (add) andO (alcohol)203 1 (add) and 1 (alcohol)181 1 (add)194 . These contradictory results could be partly due to the low solubility of terephthalic acid in 1,2-ethanediol. 

The oxidation by Mn(Iir) in a perchlorate medium follows two kinetic paths depending on the bromide concentration, viz. 

The direct reduction of Cu(Il) acetate to Cu(I) by CO at high pressures (up to 1360 atm) in aqueous solution at 120 °C shows several kinetic paths, the rate... 

We use these relations instead of Equations 13.5-13.7 when tracing a kinetic path. 

Irradiation of DAX in pentane with a nitrogen laser creates a transient species whose spectrum is quite similar to that of the species formed by the low temperature irradiation. The half-life of this intermediate in very dry solvent is ca 50 ps. Its reaction under these conditions follows a complex kinetic path that gives ultimately dimeric azine and bi-xanthylidene (22). These findings help in the assignment of a structure to the transient. Neither XAH" or XAH+ are expected to give these products, but XA easily accounts for both. 

Irradiation of DMDAF in benzene solution at room temperature generates a transient intermediate that appears within the rise-time of the laser and decays by a pseudo first-order kinetic path with a half-life of 51 ns. The optical spectrum of the intermediate is essentially the same as that observed in the low temperature irradiation experiment. 

Thus, there are two kinetic paths for the hydrogen evolution. The first path consists of charge transfer (CT) followed by chemical desorption (CD) path CT-CD. The second path consists of charge transfer (CT) followed by electrochemical desorption (ED) path CT-ED. Within each path, either of the consecutive steps can be slow and thus can be the rate-determining step (RDS). Each of these paths has two pKJSsible mechanisms. 

Hydrolyses of Schiff Bases. The behavior of Schiflf bases and their complexes has been sufficiently studied so that the similarities of the kinetic paths of their hydrolyses can be clearly delineated. The reaction is interpreted in terms of a change in the rate determining step as the pH is changed. In neutral solutions the rate determining step is considered (7) the hydration step ... 

It is impossible to understand all the complicated kinetic paths and to determine the elementary reaction rate constants without a detailed quantitative investigation of all the donor-acceptor interactions in the reaction system. Strictly speaking, at present there are no data on the elementary reaction rate constants even in low-molecular model systems. 

The thermodynamic path presented in Figure 5.1 will most likely not be the same as the kinetic path . For instance, the reaction may take place in several stages involving complex systems of reaction chains, etc. Nevertheless, the energy evolved depends only on the initial and final states and not on the intermediate ones. Once the reaction is completed, the net heat evolved is exactly the same as if the reactant molecules were first dissociated into their atoms, and then reacted directly to form the final products (Hess s Law). The heats of formation of some primary and secondary explosive substances are presented in Table 5.11. 

Scheme 20 [103] shows that the polymerization of 131 proceeds via a stable tris(alkylthio)carbenium ion 135. This species can be attacked in three different ways by the second monomer, producing 134, 133, and 132 via paths a, a, and b, respectively. Kinetically, path a should dominate over the others. Path a is one of the possible pathways, but presumably it is of minor importance. Although the conversion of 134 to 132 cannot be ruled out, 132 is more likely to be formed via path b, as is the case with six-membered spiro orthocarbonates. At high... 

Because of the possible complexity of the electrode process no general treatment is possible, but some of the main concepts may be illustrated in terms of a simple model in which we shall assume a definite kinetic path. Let us consider an electrolysis system that consists of an inert metal electrode in contact with oxidized and reduced forms of a dissolved ionic species which can react at the electrode according to the stoichiometric equation... 

The hyperspherical and related coordinates which have been considered in this work have served for the visualization of critical features of potential energy surfaces [91,92], crucial for the understanding of reactivity (role of the ridge [93] and the kinetic paths [94]). In [95], the PES for the O + H2 reaction was studied. A discrete hyperspherical harmonics representation is presented in [96] for proton transfer in malonaldehyde. 

V. Aquilanti and S. Cavalli, Hyperspherical analysis of kinetic paths for elementary chemical reactions and their angular momentum dependence. Chem. Phys. Lett., 141 309-314, 1987. 

V. Aquilanti, S. Cavalli, G. Grossi, V. Pellizzari, M. Rosi, A. Sgamellotti, andF. Tarantelli, Potential energy surfaces in hyperspherical coordinate abinitio kinetic paths for the 0(3P) + H2 reaction. Chem. Phys. Lett., 162 179-184, 1989. 

The short kinetic path length because of the high one-directional transport velocity of polymerizable species. 

Influence of the Kinetic Path Length on Properties of Coating... 

In this reaction scheme, CH4 is produced by two steps of radiative association with slow rate constants. Because the destruction of C by electron capture (radiative) is four orders of magnitude slower than the destruction of a molecular ion by dissociative recombination, there is not a rapid loss of C , allowing production of a saturated hydrocarbon. We recall that chemical equilibrium arguments predict preponderant conversion of carbon monoxide to methane and water. There is little evidence for this, as stated earlier. The gas-phase production of CH4 from CO and H2 then proceeds by a very high-energy kinetic path, namely He + CO = C +... 

The most recent computations of chemical reaction paths couple chemical kinetics, path calculations, and fluid flow models. This can be accomplished by alternating between fluid flow and reaction path calculations in small time steps, with reaction kinetics included as we have described above. Several examples of this type are summarized by Brimhall and Crerar (1987, pp. 302-306). With this kind of approach it should ultimately become possible to model the detailed physical and chemical evolution of quite complex natural mineral systems. With inclusion of three-dimensional space as well as temperature and pressure gradients, there are challenges for the foreseeable future. 

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