A discussion of the first law of thermodynamics for open systems

Abstract

In this paper it is discussed to what extent the first law of thermodynamics is a physical law, and to what extent it is a definition, if it is generalized so as to be valid for open systems. The conclusion is reached that it is partly a definition. Different generalizations of the first law, which can be proposed, must be considered as different definitions. The usefulness of these different definitions is compared with respect to the shift of arbitrary constants in the internal energy and in view of the thermodynamics of irreversible processes.