We present the results of a quantum molecular dynamics simulation of the chemistry of HMX, a high performance explosive, at a density of 1.9 g/cm(3) and temperature of 3500 K, conditions roughly similar to the Chapman-Jouget detonation state. The molecular forces are determined using the self-consistent-charge density-functional-based tight-binding method. Following the dynamics for a time scale of up to 55 ps allows the construction of effective rate laws for typical products such as H2O, N-2, CO2, and CO. We estimate reaction rates for these products of 0.48, 0.08, 0.05, and 0.11 ps(-1), respectively. We also find reasonable agreement for the concentrations of dominant species with those obtained from thermodynamic calculations, despite the vastly different theoretical underpinning of these methodologies.