The investigation of thermodynamic parameters of kinetic reaction between o-phenylenediamine and gold (III)

Abstract

A visible spectrophotometric method has been developed for the reaction kinetics of o-phenylenediamine in the presence of gold (III). The method is based on the measurement of the absorbance of the reaction o-phenylenediamine and gold (III). Optimum conditions for the reaction were established as pH 6 at λ = 466 nm. When the reaction kinetic of o-phenylenediamine by gold (III) was investigated, it was observed that the following rate formula was found as ln ( A/ A 0) = − kt, according to absorbance measurements. The activation energy E a and Arrhenius constant A were calculated from the Arrhenius equation as 1.009 kJ · mol −1 and 3.46 · 10 −2 s −1, respectively. Other activation thermodynamic parameters, entropy, Δ S (J · mol −1 · K −1), enthalpy, Δ H (kJ · mol −1), Gibbs free energy, Δ G (kJ · mol −1) and equilibrium constant, K e were calculated at T = (283.2, 303.2, 323.2, and 343.2) K. The study was exothermic due to the decrease of entropy and was a non-spontaneous process during activation.