Study of the Kinetics and Activation Parameters of Reduction of Mn(III) to Mn(II) by SO₃^2- Ion in (MnSiW₁₁O₄₀H₂)^5- Heteropoly Ion

K. Ali and U. Ashiq*

Department of Chemistry, University of Karachi, Karachi, Pakistan.

(Received 29 September 2003, Accepted 10 November 2003)

      In order to gain an insight into the mechanism of reduction of Mn(III) heteropoly ions, and also to establish the conditions for use of some of these ions as oxidizing agent, following measurements have been made. The pseudo-first order rate constants, k_obs, have been determined and specific rate constants, k, were calculated from the plots of k_obs against SO₃^2- concentrations. A plot of ln(k₂/T) against inverse temperature gives enthalpy of activation as 10.67  kJ  mol^-1  and  entropy  of  activation  as  -237.90  J K^-1mol^-1. Effects of ionic strength and pH have also been studied over a limited range.

Keywords: Heteropoly ion, Stopped-flow, MPLIX program, Rate constant, Enthalpy, Entropy