The way in which reagents are mixed can have a large influence on the product distribution of chemical reactions and the size distribution of particles of the solid product. To model effects of mixing on various scales on the course of chemical reactions and precipitation processes, a nonequilibrium multiple-time-scale mixing model and a beta distribution of the mixture fraction are applied in combination with a simple conditional moment closure based on linear interpolation of local instantaneous reactant concentration values. The mixing model is linked to CFD (standard k-is an element of model) and the model predictions are compared with experimental data for fast parallel chemical reactions and barium sulfate precipitation both carried out in the single-feed semibatch stirred-tank reactor.