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

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/A0) = −kt, according to absorbance measurements. The activation energy Ea 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, ΔS (J · mol−1 · K−1), enthalpy, ΔH (kJ · mol−1), Gibbs free energy, ΔG (kJ · mol−1) and equilibrium constant, Ke 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.