The objective of this project was to predict the yield of a reactor operated under turbulent flow conditions with a Newtonian liquid in which reagents and products have been dissolved. There are no restrictions on the complexity of reactions. To predict the results of coupled reactions the approach chosen for modelling is a Lagrangian description of reaction zones in a Eulerian flow field. This means that the paths of reaction zones through the reactor (a stirred tank reactor) are tracked. The paths are determined by the average flow field and the turbulent flow properties. This flow field is calculated in a Eulerian way. The Eulerian flow field is verified experimentally by means of Laser Doppler Anemometry. As the reactions take place at and below the Kolmogorov scales, a description of this small-scale flow serves as a model for the reaction zones. This small-scale flow is believed to show a universal behaviour consisting of vortex tubes. For low turbulence intensity regions Laser Induced Fluorescence visualizations show mainly a single exponentially shrinking single layer containing the added fluid, which is accordance with a Cylindrical Strectched Vortex description of the small scales for these regions. Using such a one-dimensional description the yield of a parallel reaction set could be predicted satisfactorily. For a prediction of the yield in the high intensity regions the full two-dimensional Cylindrical Strectched Vortex model may be needed.