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** Activated complex theory reaction rate **

** Chemical reactions activated complex theory **

** Chemical reactions reaction rates **

The activated complex theory of reaction rates in dilute gas mixtures is based on the statistical mechanical theory of chemical equilibrium. [Pg.1081]

The effect of pressure on reaction rate constant k can be explained by the activated complex theory. The theory postulates that the elementary chemical reactions occur via a transition state, such as A + B -> products, in which the reactants and transition state are assumed to be in equilibrium. The transition state (activated complex), Ivt, is defined as the state of the maximum energy along the reaction path reaction coordinate). The rate constant can be expressed as follows, based on the activated complex theory, [Pg.119]

The situation for a chemical, as opposed to an electrochemical, reaction is considered first. Simplified activated complex theory assumes an Arrhenius-type dependence of the forward rate constant, kf, on the chemical free energy of activation, AC, according to the following equation [Pg.34]

Now, according to the transition-state theory of chemical reaction rates, the pre-exponential factors are related to the entropy of activation, A5 , of the particular reaction [A = kT ere k and h are the Boltzmann and Planck constants, respectively, and An is the change in the number of molecules when the transition state complex is formed.] Entropies of polymerization are usually negative, since there is a net decrease in disorder when the discrete radical and monomer combine. The range of values for vinyl monomers of major interest in connection with free radical copolymerization is not large (about —100 to —150 JK mol ) and it is not unreasonable to suppose, therefore, that the A values in Eq. (7-73) will be approximately equal. It follows then that [Pg.268]

A more detailed form for writing the equation for parameter 8y can be based on the activated complex theory. The said theory predicts the following dependence for the rate of elementary chemical reaction i j [Pg.22]

A useful way to do this is to use the transition state theory of chemical reaction rates (e.g., see Glasstone, Laidler, and Eyring [55] also, for a current review, sec Laidler [56]). This is based on the hypothesis that all elementary reactions proceed through an activated complex [Pg.61]

The simple collision theory and the activated complex theory have appeared as two alternative treatments of chemical reaction kinetics. It is clear, however, that they represent only two different kinds of approximation to an exact collision theory based either on classical or quantum mechanics. During the past few years considerable progress has been achieved in the colllsional treatment of bimole-cular reactions /7,8/. For more complicated reactions, however, the collision theory yields untractable expressions so that the activated complex theory provides a unique general method for an estimation of the rates of these reactions. Therefore, it is very important to determine well the limits of its validity. [Pg.4]

Collision state theory is useful for gas-phase reactions of simple atoms and molecules, but it cannot adequately predict reaction rates for more complex molecules or molecules in solution. Another approach, called transition-state theory (or activated-complex theory), was developed by Henry Eyring and others in the 1930s. Because it is applicable to a wide range of reactions, transition-state theory has become the major theoretical tool in the prediction of chemical kinetics. [Pg.742]

Isotope effects on rates (so-called kinetic isotope effects, KIE s) of specific reactions will be discussed in detail in a later chapter. The most frequently employed formalism used to discuss KIE s is based on the activated complex (transition state) theory of chemical kinetics and is analogous to the theory of isotope effects on thermodynamic equilibria discussed in this chapter. It is thus appropriate to discuss this theory here. [Pg.117]

As a result of the development of quantum mechanics, another theoretical approach to chemical reaction rates has been developed which gives a deeper understanding of the reaction process. It is known as the Absolute Reaction Rate Theory orthe Transition State Theory or, more commonly, as the Activated Complex Theory (ACT), developed by H. Eyring and M. Polanyi in 1935. According to ACT, the bimolecular reaction between two molecules A2 and B2 passes through the formation of the so-called activated complex which then decomposes to yield the product AB, as illustrated below [Pg.68]

Other than the requirement that substances must be able to react, what conditions affect the rates of chemical reactions Recall the collision theory. In order to react, particles of reactants must have an opportunity to collide, they must collide in the right orientation, and they must collide with enough energy to form an activated complex. [Pg.171]

Transition-state theory is one of the earliest attempts to explain chemical reaction rates from first principles. It was initially developed by Eyring [124] and Evans and Polayni [122,123], The conventional transition-state theory (CTST) discussed here provides a relatively straightforward method to estimate reaction rate constants, particularly the preexponential factor in an Arrhenius expression. This theory is sometimes also known as activated complex theory. More advanced versions of transition-state theory have also been developed over the years [401], [Pg.415]

The first of the theoretical chapters (Chapter 9) treats approaches to the calculation of thermal rate constants. The material is familiar—activated complex theory, RRKM theory of unimolecular reaction, Debye theory of diffusion-limited reaction—and emphasizes how much information can be correlated on the basis of quite limited models. In the final chapt, the dynamics of single-collision chemistry is analyzed within a highly simplified framework the model, based on classical mechanics, collinear collision geometries, and naive potential-energy surfaces, illuminates many of the features that account for chemical reactivity. [Pg.373]

Many theories of kinetics have been constructed to illuminate the factors controlling reaction rates, and a prime goal of these theories is to predict the values of A and for specific chemical systems in terms of quantitative molecular properties. An important general theory that has been adapted for electrode kinetics is the transition state theory, which is also known as the absolute rate theory or the activated complex theory. [Pg.90]

A "diatomic model for radical-radical recombination seems to be a good approximation as well. Therefore, lor such reactions the maximum of the effective potential energy (8.IV), including a centrifugal potential, allows us to define a transition state (or "activated complex). This provides the possibility for an application of either the colli-sional or statistical formulations of the theory of chemical reaction rates these formulations will be compared in the following sections. [Pg.243]

Our approach is very simple, but it has the virtue of providing exact general rate expressions which are closely related to the traditional formulations of both the collision and activated complex theory as given by equations (3A) and (5A), respectively. Thus, it directly yields precise definitions of both the quantum and classical (or semiclassical) corrections to be introduced in these equations, as well as in the properly adiabatic formulations of transition state theory also discussed in this book. We hope, therefore, that the unified treatment presented will contribute to a full elucidation of the relations between the various theories of chemical reaction rates. [Pg.7]

** Activated complex theory reaction rate **

** Chemical reactions activated complex theory **

** Chemical reactions reaction rates **

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