Controlled by kinetics

This last inflammability parameter presents problems. After stating its definition it will be seen that measuring autoignition temperature proves to be a difficult exercise because its measurement is sensitive to the experimental conditions, even more sensitive than for flashpoints. Worse, this parameter seems to be controlled by kinetic factors far more complex to master than the thermodynamic factors that probably control flashpoints (in fact it is a liquid/vapour equilibrium). So whilst the influence of the nature of the cup metal on a flashpoint has never been demonstrated, this demonstration was easily made with autoignition temperatures. 

Selectivity at formation of a respective inclusion compound and its thermal stability behavior might differ (cf. Tables 1 and 2), since for both representations different processes should be taken into consideration. Formation of a crystal inclusion compound is normally controlled by kinetics, whereas the thermal stability (decomposition property) is a result of thermodynamics. Thus, we speak of formation selectivity , on the one hand, and of binding selectivity , on the other. 

It is shown that the first step in the electrochemical reduction of cathodic material CoxOy(OH)z in power sources is controlled by kinetics. This process at the interface depends on the catalytic activity of compound, Figure 7 (a) the reduction of the bulk of cathodic materials is controlled by diffusion Figure 7 (b). 

To formulate a kinetic reaction path, we consider one or more minerals A whose rates of dissolution and precipitation are to be controlled by kinetic rate laws. We wish to avoid assuming that the minerals A- are in equilibrium with the... 

The important effect of increasing pressure on the kinetics of chemical reactions has been noted since the hrst chemical experiments at high pressure. The simplest expectation derives from the observation that in liquids the viscosity rapidly increases with pressure. As a result, in strongly compressed liquids, and hnally in glasses, diffusion-controlled processes can be retarded. In contrast, however, other reaction pathways can be substantially accelerated. In general, the evolution of a reaction at high pressure can be heavily controlled by kinetic aspects, and these deeply involve intermolecular effects. 

Such equilibria are governed by thermodynamics, and so the abundances of the different species in solution are dependent on their relative thermodynamic stabilities. If, however, such a mixture of species is applied in, for example, a conjugate addition reaction, the product formation will be controlled by kinetics, and it is most likely that Cu2Li2Mc4 would be kinetically the most active species present. 

Some of the disagreement in the metal binding work may arise from uncertainties as to whether binding was controlled by kinetics or thermodynamics. To illustrate what is meant, consider the addition of one zinc ion to apoenzyme. Is the site where this zinc ion is bound the most stable site or the one most accessible Evidently this might depend upon the time, and whether or not the concentration of zinc is controlled by a chelating agent. 

Hydrate growth (Section 3.2), which may be controlled by kinetic, heat,... 

As an example of hydrate nucleation and growth, consider the gas consumption versus time trace in Figure 3. la for an agitated system operated at constant pressure and temperature. An autoclave cell (e.g., 300 cm3) containing water (e.g., 150 cm3) is pressurized with gas and brought to hydrate formation (P, T) conditions. The gas is added from a reservoir to maintain constant pressure as hydrates form with time. The rate of consumption of gas is the hydrate formation rate that can be controlled by kinetics, or heat or mass transfer. 

The chemical reaction is very slow the experimental current is controlled by kinetics because the formation of O is very small, thus not giving the system the chance to build up a diffusion layer. In this case, a broad wave rather than a peak is observed. 

The use of sterically hindered bases raises the activation energy barrier for the pathway to the product predicted by Saytzeffs Rule. Thus, a sterically hindered base will preferentially react with the least hindered protons, and the product distribution will be controlled by kinetics. 

In the first step, stereochemical information contained in a matrix-complex is transferred to the substrate by the formation of a matrix-substrate complex in such a way that the substrate in the second step will be able to differentiate the direction of attack of a reagent. In the reaction chain the MS-complex may appear as an intermediate or a transition state. The transition from the MS-complex to the product may proceed in a reversible or in a nonreversible reaction. Therefore the product ratio of an asymmetric synthesis is not necessarily controlled by kinetic parameters, although this may often be the case. 

Generally, second-row metal clusters do not need to be thermally activated to afford CO substitution. The degree of substitution in these clusters therefore can often be controlled by kinetic factors, such as concentration and ratio of the reagents as well as reaction times. In this way high yields of each compound in the series Ru6C(CO),7 , P(OMe)3 (n = 1-4) (52) and Rh6(CO),i6-2n)(L L) (n = 1, 2, 3, L-L = dppm) (179) have been obtained. For HNCC of the heavier metal atoms, however, thermal activation must be employed. Because the temperatures necessary to activate CO substitution... 

The implication of these studies is of critical importance. Chemists generally think of the product distribution of a chemical reaction being controlled by kinetics or thermodynamics. Under kinetic control, the distribution favors the product that results from crossing the lowest activation barrier. Under thermodynamic control, the distribution favors the lowest energy product. Schreiner and Allen now add... 

Although crystallization is controlled by kinetic factors, it is a phenomenon that is thermodynamic in origin (a first-order phase transition). On the other hand, the glass transition may be purely kinetic. We ll say more about that shortly, but one manifestation of this is the dependence of the T on the rate of cooling. It is observed at a somewhat lower temperature if a sample is cooled slowly than if it is cooled quickly (Figure 10-16). 

It is often desirable, where applicable, to use the local equilibrium assumption when predicting the fate of subsurface solutes. Advantages of this approach may include 1) data such as equilibrium constants are readily available, as opposed to the lack of kinetic data, and 2) for transport involving ion exchange and adsorption, the mathematics for equilibrium systems are generally simpler than for those controlled by kinetics. To utilize fully these advantages, it is helpful to know the flow rate below which the local equilibrium assumption is applicable for a given chemical system. Few indicators are available which allow determination of that critical water flux. 

We also saw in Section 12.16 that lithium, although it is the strongest reducing agent, reacts more slowly with water than sodium or potassium. From the discussions in Chapters 10 and 15, we know that the equilibrium position for a reaction (in this case indicated by the %° values) is controlled by thermodynamic factors, but that the rate of a reaction is controlled by kinetic factors. There is no direct connection between these factors. Lithium reacts more slowly with water than sodium or potassium because as a solid lithium has a higher melting point than either of the other elements. Since lithium... 

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