Determination of rate constant and diffusivity in heterogeneous isotopic exchange reaction

Abstract

The rate constant and particle self-diffusion coefficient of a heterogeneous isotopic exchange reaction are determined by the method suggested from a solution to the diffusion equation for a composite sphere in a limited bath. The values of the kinetic parameter, ζ 1 (ratio of forward surface mass reaction rate to intraparticle diffusion rate), particle self-diffusion coefficient, D, and rate constant, k, are obtained for the isotopic exchange reaction of the system CaCO 3(s) Ca 2+ (aq) at 25, 35 and 45°C by measuring the self-exchange reaction rate using 45Ca as a tracer. The values of D and k are calculated to be 0.87 × 10 −12 to 1.8 × 10 −12 cm 2/sec and 0.089 to 0.020 cm 3/mole sec, respectively, as the temperature is raised from 25 to 45°C. The activation energies for the surface mass reaction and the intraparticle diffusion are also calculated to be 7.2 and 6.3 kcal/mole, respectively.