Absolute-rate theory

Rosenstock H M, Wallenstein M B, Wahrhaftig A L and Frying H 1952 Absolute rate theory for isolated systems and the mass spectra of polyatomic molecules Proc. Natl Acad. Sci. USA 38 667-78... 

Mies F H 1969 Resonant scattering theory of association reactions and unimolecular decomposition. Comparison of the collision theory and the absolute rate theory J. Cham. Phys. 51 798-807... 

Finally, exchange is a kinetic process and governed by absolute rate theory. Therefore, study of the rate as a fiinction of temperature can provide thennodynamic data on the transition state, according to equation (B2.4.1)). This equation, in which Ids Boltzmaim s constant and h is Planck s constant, relates tlie observed rate to the Gibbs free energy of activation, AG. ... 

The most widely accepted treatment of reaction rates is transition state theory (TST), devised by Henry Eyring.17 It has also been known as absolute rate theory and activated complex theory, but these terms are now less widely used. 

This mechanism is given in equation (37). Absolute rate theory leads to equation (55), and making the same assumption as for the A1 case, equation (50), leads to the relevant rate equation, equation (56).145,161 This equation is derived on the assumption that all the acidity of the medium comes from solvated protons , H30+ in sulfuric acid it will require modification above 80 wt% acid as the medium acidity begins to be due to the presence of undissociated H2S04 molecules as well, see above.179... 

While the collision theory of reactions is intuitive, and the calculation of encounter rates is relatively straightforward, the calculation of the cross-sections, especially the steric requirements, from such a dynamic model is difficult. A very different and less detailed approach was begun in the 1930s that sidesteps some of the difficulties. Variously known as absolute rate theory, activated complex theory, and transition state theory (TST), this class of model ignores the rates at which molecules encounter each other, and instead lets thermodynamic/statistical considerations predict how many combinations of reactants are in the transition-state configuration under reaction conditions. 

Consider the adsorption of a species A with concentration ca in the bulk of the solution. The variation of the coverage 9 with ca, keeping all other variables fixed, is known as the adsorption isotherm. We regard the adsorption process as a reaction between the free sites on the electrode, whose number is proportional to (1 — 6), and the species A in the solution. Using absolute rate theory, we can write the rate of adsorption as ... 

The results are shown in Table 9. Based on absolute rate theory Rossi et a/.117a give AS for reaction (1) as 14.2+2.6 e.u. The mechanism proposed is... 

Rosenstock, H.M. Wallenstein, M.B. Wahihaftig, A.L. Eyring, H. Absolute Rate Theory for Isolated Systems and the Mass Spectra of Polyatomic Molecules. 

The measurement of exchange rates is important, since it gives us vital information on the transition state between reagents and products. Absolute rate theory states that the rate is given by eq. (1), in which k, h and R are Boltzmann s, Planck s and the gas constants, and T is the absolute temperature. The transmission coefficient, k, is usually taken as 1. The thermodynamic functions AG, AH and AS represent the change between the initial and transition states. 

In terms of the vibrational partition functions Q of the reactants ( and ") and of the activated complex ( ), the Absolute Rate Theory expression for k° is... 

Complex Theory, known also as Transition State Theory. See Absolute Rate Theory in Vol 1 of Encycl and in Cook (1958), p 134... 

Activated Complex Theory of Reaction Rates. Same as Absolute Rate Theory, described in Vol 1 of Encycl, p A4-R... 

Eyring (1935a, b) developed Transition State Theory , or Absolute Rate Theory , in the 1930s. 

According to Eyring s absolute rate theory (1), in which there is postulated the establishment of a quasiequilibrium between the reactants and an active complex, the rate constant may be expressed as... 

Absolute Rate Theory(also known as Transition State or Activated Complex Theory). A theory of reaction rates based on the postulate that molecules form, before undergoing reaction, an activated complex which is in equilibrium with the reactants. The rate of reaction is controlled by the concn of the complex present at any instant. In general, the complex is unstable and has a very brief existance(See also Collision Theoty of Reaction)... 

Activated Carbon orCharcoal. See Carbon (or Charcoal) Activated Activated Complex Theory. See Absolute Rate Theory... 

Eyring absolute reaction rate theory see Absolute rate theory 1 A4 6 E508... 

APPLICATION OF ABSOLUTE RATE THEORY TO BIMOLECULAR SURFACE REACTIONS... 

The application of Absolute Rate Theory to the interpretation of catalytic hydrogenation reactions has received relatively little attention and, even when applied, has only achieved moderate success. This is, in part, due to the necessity to formulate precise mechanisms in order to derive appropriate rate expressions [43] and, in part, due to the necessity to make various assumptions with regard to such factors as the number of surface sites per unit area of the catalyst, usually assumed to be 10 5 cm-2, the activity of the surface and the immobility or otherwise of the transition state. In spite of these difficulties, it has been shown that satisfactory agreement between observed and calculated rates can be obtained in the case of the nickel-catalysed hydrogenation of ethylene (Table 3), and between the observed and calculated apparent activation energies for the... 

As noted in Sect. 2.2 (p. 5) the determination of the kinetic parameters cannot of itself lead to the specification of a complete mechanism, although any postulated mechanism must be compatible with the kinetics. Furthermore, the interpretation of kinetic parameters in terms of absolute rate theory [42] has not, in general, been successful. 

The transport process within the zeolite pore system involves the passage of sorbate molecules through the windows between adjacent cavities. For molecules with critical diameters similar to the free aperture of the window ( 4.2 A for type A zeolites), an activated diffusion process is to be expected, and a molecule at the center of the window may be identified as the transition state. For the A-type lattice the following expression for the limiting diffusivity may be derived from absolute rate theory (14)... 

According to the absolute rate theory, the rate of the overall reaction corresponding to eqn. (126) is equal to the rate of decomposition of the activated complex corresponding to the highest activation barrier. 

The rate coefficient for a heterogeneous electron transfer reaction at an electrode can be written, according to the absolute rate theory [54], as... 

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