Theoretical investigation of a mechanically stimulated self-propagating reaction (MSR) has been carried out for the Zn-S system. The densities of heat sources at impact-friction contacts of zinc particles coated with sulfur were calculated based on an anomalous increase in sulfur viscosity caused by its polymerization taking into account the heat effect of Zn-S formation. The obtained densities of heat sources of viscous flow and chemical reaction where comparable with the density of the dry friction source in the order of magnitude.