Homogeneous activation free energy

It therefore seems reasonable that the deviations of the activation free energies for highly exoergic electrochemical and homogeneous reactions, illustrated in Figures 2 and 5, may arise partly from the same source, i.e., from values of for the oxidation half reactions that are unexpectedly small. That is not to say that other factors are not responsible, at least in part, for these discrepancies. Nonadiabaticity, work terms, specific solvation, and other environmental effects may all play important roles depending on the reactants. For example, there is evidence to suggest that the true rate constant for outer-3+/2+... 

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 final step of the convolution analysis is the determination of the transfer coefficient a. This coefficient, sometimes called the symmetry factor, describes how variations in the reaction free energy affect the activation free energy (equation 26). The value of a does not depend on whether the reaction is a heterogeneous or a homogeneous ET (or even a different type of reaction such as a proton transfer, where a is better known as the Bronsted coefficient). Since the ET rate constant may be described by equation (4), the experimental determination of a is carried out by derivatization of the ln/Chet-AG° and thus of the experimental Inkhei- plots (AG° = F E — E°)) (equation 27). 

The forward activation free energy is determined along the same lines as presented for homogeneous electron transfer since both problems are strictly equivalent [43,44,78,79]. Thus, is given as a function of the local driving force [AG° in Eq. (104)] and of the associated reorganization energy A by the expression in Eq. (105), which derives from Eq. (64). 

For homogeneous nucleation, activation free energy required for the formation of a stable nucleus... 

For the homogeneous nucleation of a spherical solid particle in a liquid solution, expressions for the critical radius (r ) and activation free energy (AG ) are represented by Equations 10.3 and 10.4, respectively. These two parameters are indicated in the plot of Figure 10.2b. 

The activation free energy for heterogeneous nucleation (AGhet) is lower than that for homogeneous nucleation (AGhom) a demonstrated on the schematic free energy-versus-nucleus radius cm es of Figure 10.6. 

Marcus s model assumes the validity of a linear response approximation and that a continuum electrostatic description of the interface is suitable for the purpose of calculating the activation free energy. Furthermore, to obtain expressions for the rate constant, the interface is assumed to be either a mathematically sharp plane or a broad homogeneous phase. Unfortunately, an insufficient... 

The concept of substance activity was derived by Gilbert N. Lewis in 1907 from the laws of equilibrium thermodynamics and is described in detail in the text entitled Thermodynamics and the Free Energy of Chemical Substances by Lewis and Randell (1923). In a homogeneous mixture, each component has a chemical potential (jjl), which describes how much the free energy changes per mole of substance added to the system. The chemical potential of water (pw) in a solution is given by... 

Intrinsic free energy of activation for homogeneous self-exchange, obtained from values of corr giVen in Table 1 using AGih = "RT ln(kcorr/Zh) where 2 x 1()11, -1 ... 

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