The Role of Kinetics

Because thermodynamics deals only with equilibrium states, we can use it to show, for example, that calcite should dissolve in a certain solution, or that it should precipitate from another solution, but we are unable to say anything whatsoever about how fast such processes will occur, or indeed if they will occur at all (metastable supersaturated solutions are well known, after all). This is a serious limitation. Many important processes may be rate-limited by one or more slow reactions. 

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The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

Currently this model is one of the most commonly used in the theory of free-radical copolymerization. The formation of a donor-acceptor complex Ma... iVlbetween monomers Ma and in some systems is responsible for a number of peculiarities absent in the case of the ideal model. Such peculiarities are due to the fact that besides the single monomer addition to a propagating radical, a possibility also exists of monomer addition in pairs as a complex. Here the role of kinetically independent elements is played by ultimate units Ma of growing chains as well as by free (M ) and complex-bound (M ) monomers, whose constants of the rate of addition to the macroradical with a-th ultimate unit will be... 

In this case the role of kinetically independent elements in accordance with the extended Flory principle is performed by monomeric units of different kinds S0,...,Sf, while here the rate constants of the elementary reactions of condensation ky(z, =0,...,f-l) between functional groups belonging to units S and S act as the parameters of the FSSE model. It has been suggested [76] to characterize every molecule by vector 1 with components /0,...,/(,...,Zf equal to the numbers of units of types S0,...,S ,...,Sf that this molecule is comprised of. Kinetic schemes of the reactions between monomeric units as well as between molecules may be written down as follows ... 

It has been known for some time that Ag2+ ions could be stabilized by the use of strongly addic conditions.531 Studies in perchloric, sulfuric and phosphoric adds have emphasized the importance of silver(II)-solvent complexes and the role of kinetic factors in determining the lifetime of Agu with regard to its reduction by water.532,533... 

Polymorphic structures of molecular crystals are different phases of a particular molecular entity. To understand the formation of those phases and relationships between them we make use of the classic tools of the Phase Rule, and of thermodynamics and kinetics. In this chapter we will review the thermodynamics in the context of its relevance to polymorphism and explore a number of areas in which it has proved useful in understanding the relationship between polymorphs and polymorphic behaviour. This will be followed by a summary of the role of kinetic factors in detecting the growth of polymorphic forms. We will then provide some guidelines for presenting and comparing the structural aspects of different polymorphic structures, with particular emphasis on those that are dominated by hydrogen bonds. 

The uncertainty associated with the interpretation of the impedance response can be reduced by using an electrode for which the current and potential distribution is uniform. There are two types of distributions that can be used to guide electrode design. As described in Section 5.6.1, the primary distribution accounts for the influence of Ohmic resistance and mass-transfer-limited distributions account for the role of convective diffusion. The secondary distributions account for the role of kinetic resistance which tends to reduce the nonuniformity seen for a primary distribution. Thus, if the primary distribution is uniform, the secondary... 

The preferred structure of a carbocation is planar, and the nature of the bridgehead position is such that any carbocation formed at the bridgehead is unable to become planar. This raises the question of how easy is it to form a bridgehead carbocation The role of kinetics is significant... 

Middleton, J.C. Cooke, M. Litherland, L. The role of kinetic energy in gas-liquid dispersion. In Institute of Chemical Engineering Symposium Series, No. 136, Proceedings of the 8th European Mixing Conference, Cambridge, 1994 595-602. 

Secondly, the problem of selectivity has been thoroughly scrutinized as applied to catalytic chemistry of olefins, aromatic hydrocarbons, oxygenates, etc. However, in the case of light alkanes we are facing a very different set of problems originating from relatively low reactivity of the starting molecules as compared to the molecules of the desired products. As a result, the applicability of existing approaches for the development of selective catalysts becomes doubtful and makes the role of kinetic factors crucial. 

S. Solovyov, V. Ilyashenko, and J. Pojman, Numerical modeling of self-propagating fronts of addition polymerization The role of kinetics on front stability. Chaos, 7 (1997), pp. 331-340. 

The recent ceU adhesion paradigm has been developed to emphasize the role of kinetics. Conceptualized by Bell [1978] and refined by several authors [Hammer and Lauffenburger, 1987 Dembo et al, 1988], the reaction kinetics approach integrates the adhesive interaction of the cells with the surface into the... 

The conversion of a triferrous linear triple helicate to a pentaferrous circular heUcate with the addition of chloride as a guest for the larger structure has been observed. In this system, the helicate is determined to be a kinetic product during circular helicate formation. The study highlights the role of kinetic control in self-assembly processes and the complexity of possible mechanistic interpretations. 

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