Jarzynski, C. “Microscopic analysis of Clausius–Duhem processes.” *Journal of statistical physics* 96, no. 1 (1999): 415-427.

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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 Clausius–Duhem inequality, and (3) can be generalized to situations in which the system begins and/or ends in nonequilibrium states.