The detonation of high explosives often generates energetic, secondary fireballs. For CHNO explosives, the detonation products that participate in these afterburn reactions include CO, H2, CH4, NH3, etc., along with carbonaceous soot. The present work has found that there are important differences in the way that particulates (soot) mix with the surrounding air that result in reaction rates that are drastically different from those involving gas phase species. Closed vessel detonations involving small charges of C-4 and Detasheet-C were carried out, with different amounts of oxygen in the vessel’s atmosphere. The closed vessel was part of a larger calorimeter, which measured the heat evolved. A simple model that describes the evolution of heat from the gas phase and condensed phase detonation products as a function of oxygen consumption was developed, and is used to show that the condensed phase species react much more effectively in the fireball than gas phase species.