Thermochemistry and Thermodynamics of Ion Exchange in a Crystalline Exchange Medium

A simple, robust calorimeter has been constructed and used to study the heats of exchange of the ion pairs Li ⇌ Na, K ⇌ Na, Rb ⇌ Na, Cs ⇌ Na, and Ca ⇌ 2Na in Linde sieve 4 A, and parallel measurements have been made of the exchange equilibria. In all cases the thermochemical and equilibrium measurements have been interpreted to give standard heats of partial exchange, and standard heats, free energies and entropies of full exchange, which have been discussed in relation to the energetic heterogeneity of distribution of the cations and other factors. Heats, free energies and entropies of mixing of the end members of the exchange to give the mixed, solid crystalline exchangers have also been derived and discussed.