Activation energy terms

Under normal circumstances the true activation energy term in equation 12.3.85 will far exceed the diffusional activation term calculated from either equation 12.3.86 or equation 12.3.87 and, to a good approximation, it may be said that in the limit of low effectiveness factors... 

It is found that the propagation reaction has a rather low activation energy causing Ep to be much lower than Ej, Et. Therefore, the overall activation energy terms in equation (4.20) would be positive for which kR increases with decrease of the temperature. 

Assuming that we already know the mechanism of reaction and whether or not it is elementary, we may then proceed to the prediction of the frequency factor and activation energy terms of the rate constant. 

This means that the rate enhancement stems not from the activation energy term, but mainly from the entropy factors. 

A simple way of analyzing the rate constants of chemical reactions is the collision theory of reaction kinetics. The rate constant for a bimolecular reaction is considered to be composed of the product of three terms the frequency of collisions, Z a steric factor, p, to allow for the fraction of the molecules that are in the correct orientation and an activation energy term to allow for the fraction of the molecules that are sufficiently thermally activated to react. That is,... 

The saline hydrides are prepared by direct interaction at 300 to 700°C. The rates are in the order Li > Cs > K > Na, largely because of the activation energy term in the Arrhenius equation. Extremely active hydrides of Li, Na, and K can be made by interaction of hydrogen with BuLi + TMEDA in hexane (LiH) or of BuLi + M(OBu ) + TMEDA in hexane (NaH and KH). 

Since tab is the reciprocal of a unimolecular rate constant, it should be about 10 sec if we neglect activation energy. Any activation energy term can be absorbed in the experimental term. For alternate derivations see Kassel, op. city chap. 4. 

In both Equations 8.36 and 8.37, h is the average value of the flow behavior index for data at all the studied temperatures. Vitali and Rao (1984a, 1984b) showed that the activation energy terms in Equations 3 and 4 are related according to ... 

Tbe elearostatic effect may he diminished by the so-called tunneling effect (Fitch and Sbih, 1975) in which the uncharged end pulls the oligomer through the surface or reacts while the charged end still is in the aqueous phase. This may be important especially for hi er oligomers and may he calculated if the van der Waals attraction is included in the activation energy term. 

Then Ajo.kink is a constant including < ink, the kinetic constant Adep,kink. as well as the activation energy term of eq.(2.21)... 

The rate constant itself has a structure and consists of a pre-exponential term and die activation energy term as per the Arrhenius equation ... 

For isotopes of the lighter elements, the activation energy term makes the main contribution to the reaction rate isotope effect, while for the heavier elements the vibrational frequency causing the decomposition into the products plays the larger role. Because the energy states usually are more separated for the isotopic molecules of the products and reactants than for the transition state, isotope effects are usually larger in reaction kinetics than in equilibria. 

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