Journal of Statistical Physics, Vol. 96, Nos. 12, 1999. p. 415-4271.
Given a thermodynamic process which carries a system from one equilibrium state to another, we construct a quantity whose average, over an ensemble of microscopic realizations of the process, depends only on these end states, even if at intermediate times the system is out of equilibrium. This result (1) can be used to express the entropy difference between two equilibrium states in terms of an irreversible process connecting them, (2) leads to two statistical statements of the ClausiusDuhem inequality, and (3) can be generalized to situations in
which the system begins andor ends in nonequilibrium states.