A lumped parameter mathematical model has been developed, which simulates the operation of a gas-liquid stirred reactor in the transition domain between kinetic and diffusional regimes of absorption with reaction.In order to determine the rate constants and the coefficient of mass transfer, the model has been compared with experimental data for the ozonation of organic substrates in aqueous solution (maleic acid, fumaric acid and phenol). The upper working limit of the method has been determined at about Ha = 25.