The thermodynamics of complicated systems

Abstract The major aims of this paper are 1. (1) to formulate a few general principles, of use in the applications of thermodynamics to heterogeneous systems, where the properties of impermeability, rigidity and thermal insulation play an important part. 2. (2) to develop a macroscopic theory of irreversible processes applicable to systems which are not near to equilibrium. For these purposes, in addition to the conservation laws and Caratheodory's Principle, one further principle is needed, which may be stated as follows: ‘an unperturbed system tends to approach a state of equilibrium, which is completely determined by the extensive parameters in the equilibrium state’. This principle is applied to several fundamental questions concerning thermodynamical equilibrium. In the final section, a general formalism is developed for the description of irreversible processes, without requiring the usual (approximate) linear relations between fluxes and ‘forces’. Though this formalism is based on statistical considerations, it is independent of any molecular hypothesis.