Activation energy, calculation definition

Because thermodynamic quantities are commonly expressed in kj mol", we have replaced the Boltzmann constants by the gas constant, R. We calculate the activation energy (in kJ mol ) by applying the definition ... 

Calculations carried out by Gottesfeld et al. [52], who borrowed from studies of thermal desorption of H2 from Cu [56, 57], indicate that H2 rather than H20 should be a product of formaldehyde oxidation at Cu at potentials up to ca. +0.4 V vs. RHE. This is provided conditions are such that the activation energy for hydrogen recombination and desorption does not exceed 10 kcal/mole. Obviously a relatively high activation energy (which appears never to be observed at Cu) favors eventual oxidation of adsorbed H atoms, before recombinative desorption can occur. Gottesfeld et al. s calculation is interesting, but perhaps not a definitive calculation since it is... 

At 315°C. the rate constant ki has a value of 7.0 X 1016 molecules/sec.-cm.2-atm. From the definition of kh this represents the rate of adsorption of methylcyclohexane per cm.2 of bare platinum surface at a methylcyclohexane partial pressure of 1 atm. From kinetic theory and statistical mechanics, one can calculate the number of molecules striking a unit area of surface per unit time with activation energy Ea. This is given by... 

An attempt has been made to analyse whether the electrophilicity index is a reliable descriptor of the kinetic behaviour. Relative experimental rates of Friedel-Crafts benzylation, acetylation, and benzoylation reactions were found to correlate well with the corresponding calculated electrophilicity values. In the case of chlorination of various substituted ethylenes and nitration of toluene and chlorobenzene, the correlation was generally poor but somewhat better in the case of the experimental and the calculated activation energies for selected Markovnikov and anti-Markovnikov addition reactions. Reaction electrophilicity, local electrophilicity, and activation hardness were used together to provide a transparent picture of reaction rates and also the orientation of aromatic electrophilic substitution reactions. Ambiguity in the definition of the electrophilicity was highlighted.15... 

For the first time the reaction of CO oxidation was considered in Refs. [137,138], However, the equations for two-site processes differ from corrected Eq. (62b) due to using in these works a different definition for the bimolecular reaction activation energy the term with Ey was absent in the reaction activation energy. Actually calculations were performed with simplified assumption about s = 0 (the collision model). The theoretical curves have given a qualitative agreement with experiment data. 

As can be seen in Table 4, the "activation energy" derived from the series of exposures that includes silk fabric heated at 150°C predicts a half-life for the strain-to-break of 85 years at 20°C. The half-life at 20°C calculated from the series of exposures that covers the 70°C to 110°C range is markedly different, only 32 years. Such a large effect produced by inclusion of only one data point indicates that results obtained at this temperature may be suspect. By definition, the activation energy must be independent of temperature over the range of extrapolation. 

We now turn to the numerous observations made on the activated adsorption of hydrogen on reduced copper. In this case a definite, large temperature coefficient or activation energy Ae has been found. It was calculated by the conventional formula... 

The kinetic parameters for the n order kinetic model have been obtained using these definitions of reactivity for the pure steam gasification experiments of birch. All the activation energies lie between 228-238 kJ/mol and the reaction orders between 0.54 and 0.58, apart from definition 3. The frequency factors are somewhat more scattered, lying between 5-10 and 3-10 . Regarding the uncertainty of the calculation, definitions 2, 5 and 4 seem to give more precise results and it is interesting to notice that the error of the reaction order calculation does not depend on how a representative reactivity value is defined. 

It is very important to analyse the influence of the reactivity definition (eqn. 8 and 9) on the kinetic parameters. Since all representative reactivity definitions are related to a fixed degree of conversion (or a fixed interval), the difference between r and r will be a multiplying factor, independent of temperature and pressure, and therefore absorbed in the frequency factor. This means that whether equation 8 or 9 is used, the activation energy and the reaction order calculation will give the same result. 

The definition of the reactivity will not affect the activation energy or the reaction order calculation. 

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