The shock compression of Reactive Particle Metal Mixtures (RPMMs) is studied at the microscale by direct numerical simulation. Mixture microstructures are rendered explicitly, providing spatial resolution of the coupled thermal, mechanical, and chemical responses at the particle level during shock compression. A polymer-bonded aluminum-iron oxide thermite system is the focus of this work; however, the computational methods developed here may be extended to other reactive particle systems. Shock waves are propagated through the mixtures in finite element simulations, where Eulerian formulations are used to handle the highly-dynamic nature of particulate shock compression. Thermo-mechano-chemical responses are computed for a set of mixture classes (20% and 50% epoxy content by weight) subjected to a range of dynamic loading conditions (particle velocities ranging from 0.300??00 km/s). Two critical sub-problems are addressed: (i) the calculation of Hugoniot data for variable mixture compositions and (ii) the prediction of sites that experience microscale reaction initiation. Hugoniot calculations are in excellent agreement with experimental data. Microscale reaction initiation sites are predicted in certain load cases for each mixture class, although such predictions cannot currently be validated by experimental methods.