Abstract: The rate constant of very fast chemical reaction generally can be measured by electrochemical methods, but can not by the thin layer electrochemical methods because of the influence of diffussion effect. Long optical path length thin layer cell (LOPTLC) with large ratio of electrode area to solution volume can be used to monitor the fast chemical reaction in situ with high sensitivity and accuracy. It enables the absorption spectra to be measured without the influence of diffussion effect.
In the present paper, a fast chemical reaction of Alizain Red S (ARS) with its oxidative state ha been studied. The reaction equilibrium constant (K) under different potentials can be determined by single step potential-absorption spectra in LOPTLC. An equilibrium constant of 7.94×10~5 l·mol~(-1) for the chemical reaction has been obtained from the plot of lgK vs. (E-E~0′_1). Rate constant (k) under different potentials can be measured by single step potential-chronoabsorptionmetry. At rate constant of 426.6 l·mol~(-1)·s~(-1) for the chemical reaction has been obtained from the plot of lgK vs. (E_E~0′_1) with (E-E~0′_1)=0.