Mechanism of isotopic exchange reaction between calcium ion and calcium oxalate

Abstract

The isotopic exchange reaction of calcium ion and calcium oxalate has been studied using 45Ca as tracer. The results show that the exchange phenomenon is a complex one. The rate is controlled by the super-position of a faster interfacial ion exchange process and a slower particle diffusion process in the solid particle. The exchange reaction is affected by the condition of preparation of calcium oxalate. The activation energies of the exchange reaction at interface, and the particle diffusion in the solid, are calculated to be 9·27 kcal per mole and 7·70 kcal per mole, respectively. The activation entropy for the interface mass reaction is −19·8 e.u./mole. This negative value implies that there exists an entropy barrier in the present system. The results also indicate that the effect of recrystallization can be neglected.