We develop a model of chemical equilibrium mixtures containing the elements H, C, F, and Cl. The model is based on a recently developed equation of state for the exponential-6 fluid, combined with a simple equation of state for condensed carbon. We show that the shock response of a wide variety of molecular and polymeric fluorocarbons and chlorocarbons can be modeled as a chemical equilibrium mixture of a small number of dissociation product molecules. In particular, we predict that shocked polyvinylidine fluoride (PVF2) decomposes into a fluid phase composed mostly of HF, and a phase containing condensed carbon. HF is known to strongly associate in the supercritical fluid phase. We predict that such an association also occurs under shock conditions.