Activation free energy heterogeneous processes

My conclusion (based on double-layer theory) was that, under the usual experimental conditions, the image term is almost entirely screened off. When this is so, the dielectric contribution to the activation free energy is essentially the same for the homogeneous and the heterogeneous process. 

The phenomenon of compensation is not unique to heterogeneous catalysis it is also seen in homogeneous catalysts, in organic reactions where the solvent is varied and in numerous physical processes such as solid-state diffusion, semiconduction (where it is known as the Meyer-Neldel Rule), and thermionic emission (governed by Richardson s equation ). Indeed it appears that kinetic parameters of any activated process, physical or chemical, are quite liable to exhibit compensation it even applies to the mortality rates of bacteria, as these also obey the Arrhenius equation. It connects with parallel effects in thermodynamics, where entropy and enthalpy terms describing the temperature dependence of equilibrium constants also show compensation. This brings us the area of linear free-energy relationships (LFER), discussion of which is fully covered in the literature, but which need not detain us now. 

Because of their Gibbs free energy (see below), reaction (6.6) is shifted to the left much more than reaction (6.7). As a matter of fact, the literature shows that the equilibrium concentration of DMC in reaction (6.6) (R = Me) is less than 1 %, depending on the reaction temperature [20], whereas in reaction (6.7) it can easily exceed 20 %. Other alcohols, such as ethanol and allyl alcohol [21], show an analogous behavior. Unfavorable thermodynamics is not the only drawback of reaction (6.6) the water formed in the reaction pushes the equilibrium to the left and affects the catalyst structure and activity [20, 22,23] in both homogeneous and heterogeneous processes water traps have been used, either chemical- or process-based, and are discussed in Sect. 6.2.2.3. 

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