We report reactive Monte Carlo (RMC) simulations of reaction equilibria for both the nitric oxide dimerization and the ammonia synthesis reactions. We have applied the RMC technique to both a single bulk phase and also to a two-phase system, composed of the bulk gas and a slit-shaped pore, with pore parameters chosen to model activated carbon fibers. We achieve dose agreement with the experimentally measured conversions of nitric oxide and ammonia in the bulk phase. Both reactions involve a stoichiometric decrease in mole number, which should cause the yield of each to be enhanced by the increased density within the pore phase. We show that the effect of confinement on the yield of both reactions is significant, and is particularly dramatic for the nitric oxide reaction; in addition, the ammonia synthesis reaction is affected by the selective adsorption of nitrogen over hydrogen in the pore under certain conditions. (C) 2001 American Institute of Physics.