A stochastic coalescence-redispersion model for the simulation of chemical reactions and transport processes in heterogeneous systems is presented. In the model two adjacent cells are randomly selected, then chemical reactions are carried out in the two selected cells. The properties (mass and heat) of the two cells are then transferred. The operating parameters of the model are the frequency for pair sampling, and a partition parameter that defines the fraction of property to be transferred. The partition parameter was shown to assume the role of the transport coefficient. The model was shown to precisely simulate molecular diffusion accompanied with chemical reactions. The method was illustrated by oxidation and ignition of char in order to illustrate its usefulness in simulating steady and unsteady problems. In the present example, the bulk gas temperature was assumed 300 K and only heterogeneous oxidation was considered. Both time-dependent and steady-state solutions are given.