The aim of the work is to obtain a mathematical model describing the kinetics of a volumetric chemical reaction occurring in one or two gravity flowing films. The initial data, the rate constant of the process, the end concentration of reagents and products, as well as the geometric parameters of the reactor (volume and length) required to obtain a given degree of conversion. The model is applied in experimental data analysis for the reactions of castor oil sulphonation with sulphuric acid and cumenehydroperoxide destruction using sulphuric acid as a catalyst. Both reactions are performed in a thin film reactor. The results indicate a good agreement of the calculated data with the experimental ones, the relative deviation with respect to the concentration being less than 2 percent for the first reaction and 16 percent for the second one.