On the magnitude of ion interaction coefficients

Ciavatta [80CIA] made a compilation of ion interaction coefficients for a large number of electrolytes. Similar data for complexations of various kinds were reported by Spahiu [83SPA] and Ferri et al. [83FER/GRE], These and some other data for 25°C and 1 bar have been collected and are listed in Section B.3. 

Ciavatta [90C1A] has proposed an alternative method to estimate values of s for a first or second complex, ML or ML2, in an ionic media NX, according to the following relationships  

Ciavatta obtained [90CIA] an average deviation of 0.05 kg-mol between e estimates according to Eqs. (B.22) and (B.23) and the s values at 25°C obtained from ionic strength dependency of equilibrium constants. 

It is obvious from the data in these tables that the charge of an ion is of great importance for determining the magnitude of the ion interaction coefficient. Ions of the 

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Zeolites are somewhat like silica in their surface characteristics. Ketones and hydroxy-1,4-biradicals have very polar groups which can interact favorably with metal cations located along zeolite walls. The potential effect of the metal ions on the position of the reacting ketones is twofold. First, the cations may force a ketone molecule into a conformation or a site which it would normally not occupy based solely upon free-volume considerations. Second, the diffusion coefficient of a ketone or a hydroxy-1,4-biradical is probably much more than an order of magnitude smaller than that of benzene [289] so that the residence time of a ketone and its Norrish II intermediates in a zeolite site with at least one metal ion is expected to be closer to 100 ns than to 1 ns. 

For dissociation reactions in which the reverse, recombination step is slow, dissociation is virtually complete once the pair has separated to the contact distance. Under these conditions the magnitude of the interaction in the dissociated pair, in particular the screening of this interaction by ions, would not affect the dissociation rate. In terms of the Hammond postulate [22] and its extensions [23] an exothermic dissociation process would have its transition state close to the bound state, so that the equilibrium and recombination rate coefficients would change in parallel. In such a case one expects no salt effect on the dissociation reaction, in agreement with the classical picture of Bronsted and Bjerrum for kinetic salt effects [7]. 

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