Kinetics of the Reaction Between S20 3 and I3 in Aqueous Solution

The kinetics of the reaction between Iäaq and S^O^g has been studied under conditions of production of iodine at a known rate by the persulfate-iodide reaction and its consumption by 5..03 . The effective concentration of iodine during the steady state is measured from its reduction potential at a bright platinum foil electrode. The reaction is of first order with respect to I3~ and 5..03 individually and hence of over all second order. The specific rate is 1.51 X105 M -1 sec-1 and the frequency factor is 1.69X1012 M -1 sec-1 at 25 °C. The energy of activation for the reac­ tion is 9.58 X103 cal/mole and the entropy of activation is —2.55 cal/mole deg.