Investigation of Copper(II) – Thiosulfate Reaction Kinetics

The kinetics of reaction between copper(II) and thiosulfate ions and formation of an intermediate complex, CuS2O3 aq, are investigated. The kinetics of fading of the color of this complex has been traced spectrophotometrically using a stoppedflow apparatus. The experimental reaction order (between 2 and 2.5) shows that the mechanism involves, in the first step, fast formation of the complex and, in the second, the reaction between two complex molecules. The influence of temperature on the reaction kinetics has been studied and the reaction’s activation entropy (−214 JKmol) suggests an associative nature for the transition state.