Theory of chemical equilibrium in a lattice

The chemical equilibrium is studied for the reactionA+B?C, assuming that, initially, the particlesB form a lattice and the particlesA are statistically distributed on interstices. A mass action law is derived which defines the numbersn _A, n_B, n_C of particlesA, B,C in the chemical equilibrium assuming the initial distribution to be known. It predicts a considerably larger numbern _C of fused particlesC compared to the mass action law for the gaseous phase. The result holds for an ordinary as well as for a nuclear lattice. Its possible relevance for the production of proton-rich isotopes in the universe is discussed.