Potential work: A statistical-mechanical approach for systems in disequilibrium

A statistical measure of the maximal amount of work available from a system coupled to a reservoir is introduced and applied. The measure is valid for any initial state of the system and for any reservoir and reduces to known particular results in different limits. Any work not extracted due to irreversibility is shown to be compensated by a corresponding amount of heat. The measure of work is interpreted as the information content of the initial state. During a completely irreversible process the initial information content is degraded entirely into entropy of the reservoir (i.e., into heat). For a given change in energy it is shown that systems in thermal disequilibrium are more informative, i.e., yield more work. An explicit example, the work available from the vibrational state distribution of the nascent products of chemical reactions, is provided.