Diffusion-reaction problems potential effects

Section III focuses on problems of system topology and documents, using results obtained from a series of model calculations, how the separate influences of system size, dimensionality, and reaction pathway(s) can be disentangled, and the principal effects on reaction efficiency quantified. With these factors clarified. Section IV demonstrates how these trends and correlations change when a multipolar potential is operative between reaction partners, both confined to a compartmentalized system. More general diffusion-reaction systems are described in Section V, where effects arising from nonrandom distributions of reaction centers and, secondly, the influence of multipolar potentials in influencing catalytic processes in crystalline and semiamorphous zeolites are explored. The conclusions drawn from these studies are then summarized in Section VI. 

The real power of digital simulation techniques lies in their ability to predict current-potential-time relationships when the reactants or products of an electrode reaction participate in some intervening chemical reaction. These kinetic complications often result in a fairly difficult differential equation (when combined with the conditions for diffusion or convection encountered in electrochemical problems) that resists solution by ordinary means. Through simulation, however, the effect of any number of chemical steps may be predicted. In practice, it is best to limit these predictions to cases where the reactants and products participate in one or two rate-determining steps each independent step adds another dimensionless kinetics parameter that must be varied over the range of... 

We have only discussed two of the sixteen fields given in the figure, the prediction of the direction in which a reaction can proceed spontaneously by means of the chemical potential and the temperature and pressure dependence of p and its application. A next step would be to go over to mass action, i.e., the concentration dependence of p. This leads directly to the deduction of the mass action law, calculation of equilibrium constants, solubilities, and many other data. An expansion of the concept to colligative phenomena, diffusion processes, surface effects, electrochemical processes, etc., is easily possible. Furthermore, the same tools allow solving problems even at the atomic and molecular level that are usually treated by quantum statistical methods. 

There are features of these reactions which have attracted a great deal of attention to the problem of the coupling between outer-sphere electron transfer processes and solvent relaxation processes (a) the electron-transfer potential-energy surface is presumably somewhat cusp-like in the surface-crossing region, and this makes the reactions unusually sensitive to solvent fluctuations (b) the electron transfer step is often very fast and the bulk solvent translational diffusion properties are often not pertinent to the observed frictional effects. 

---