Transfer reactions activation energy

Static dielectric constant Electron transfer Reaction free energy Activation free energy Activation enthalpy Electronic coupling matrix element... 

Each of the following variables appears in only one dimensionless variable feed flow rate (Fo), heat transfer capacity (UA), coolant temperature (T ), recycle concentration (C3), reaction activation energy ( a)> and reaction enthalpy (-Af/)-Thus, the effect of each one can be easily investigated. 

It was suggested that a basic rule of thumb can be applied to determine which termination reaction predominates in a typical homopolymerization. Thus, polymerizations of 1,1-disubstituted olefins are likely to terminate by disproportionation because of steric effects. Polymerization of other vinyl monomers, however, favor terminations by combination unless they contain particularly labile atoms for transferring. Higher activation energies are usually required for termination reactions by disproportionation. This means that terminations by combination should predominate at lower temperatures. 

Aetivation overpotential arises from the kinetics of charge transfer reaction across the eleetrode-eleetrolyte interface. In other words, a portion of the electrode potential is lost in driving the eleetron transfer reaction. Activation overpotential is directly related to the nature of the eleetroehemical reactions and represents the magnitude of activation energy, when the reaction propagates at the rate demanded by the current. The activation overpotential can be divided into the anode and cathode overpotentials. The anode and cathode activation overpotentials are calculated from Butler-Volmer equation (3.33 and 3.34). 

Figure 5. Influence of various parameters on the region of parametric sensitivity reaction order n (A), heat transfer (B), activation energy y (C), inlet temperature 6 (E), Lewis number Le (E), interparticle mass transfer resistance Ag, [from Morbidelli and Varma (1987)].

Within this framework, by considering the physical situation of the electrode double layer, the free energy of activation of an electron transfer reaction can be identified with the reorganization energy of the solvation sheath around the ion. This idea will be carried through in detail for the simple case of the strongly solvated... 

In our simple model, the expression in A2.4.135 corresponds to the activation energy for a redox process in which only the interaction between the central ion and the ligands in the primary solvation shell is considered, and this only in the fonn of the totally synnnetrical vibration. In reality, the rate of the electron transfer reaction is also infiuenced by the motion of molecules in the outer solvation shell, as well as by other... 

Figure A3.8.3 Quantum activation free energy curves calculated for the model A-H-A proton transfer reaction described 45. The frill line is for the classical limit of the proton transfer solute in isolation, while the other curves are for different fully quantized cases. The rigid curves were calculated by keeping the A-A distance fixed. An important feature here is the direct effect of the solvent activation process on both the solvated rigid and flexible solute curves. Another feature is the effect of a fluctuating A-A distance which both lowers the activation free energy and reduces the influence of the solvent. The latter feature enliances the rate by a factor of 20 over the rigid case.

For many practically relevant material/environment combinations, thennodynamic stability is not provided, since E > E. Hence, a key consideration is how fast the corrosion reaction proceeds. As for other electrochemical reactions, a variety of factors can influence the rate detennining step. In the most straightforward case the reaction is activation energy controlled i.e. the ion transfer tlrrough the surface Helmholtz double layer involving migration and the adjustment of the hydration sphere to electron uptake or donation is rate detennining. The transition state is... 

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