The shrinking-core model for reaction control was applied to particle size distributions, particularly to the logarithmic normal distribution. Furthermore, a simultaneous comminution of the solid was considered in the model; in the first case the process of the batchwise comminution was described with a model including two kinetic parameters, in the second case a more complex material balance model was introduced and this operates with rates of breakage and distribution parameters. A comparison is given between model predictions and experimental results for the reaction of gaseous hydrogenchloride with metallurgical grade (MG) silicon to give trichlorosilane. The experimental results were obtained in a newly developed apparatus, the so-called reaction-mill, which can simultaneously act as a vibration mill and as a chemical reactor.