Fluctuations in spatially homogeneous chemical steady states

The investigation of the properties of small fluctuations serves as a basis for the generalization of equilibrium and irreversible thermodynamics, to encompass all spatially homogeneous situations of stable chemical steady states. In terms of a Gibbs ensemble picture, the reactants are coupled to particle reservoirs, often in a more intriguing way than in usual grand canonical statistics. It is shown how these couplings can be represented as generalized forces, by postulating an equipartition theorem. Response functions connected with the action of external forces are introduced, and the fluctuation–dissipation theorem is derived as a consequence of the proper definition of forces. The symmetry properties of the systems, with respect to time reversal, provide a classification scheme for the large body of possible steady states.