The “Global” Formulation of Thermodynamics and the First Law: 50 Years On

Nearly 50 years ago, Henry Bent published his groundbreaking article in this Journal introducing the “global” formulation of thermodynamics. In the following years, the global formulation was elaborated by Bent and by one of the present authors. The global formulation of the first law focuses on conservation of energy and the recognition that all energy changes involve state functions. This presentation, different from the standard, “local” formulation, has led to a deeper understanding of the foundations of thermodynamics. In this article, for the first time, a complete account of the global formulation of the first law is presented. In particular, the various possible energy changes in all subsystems that make up an experiment, including the atmosphere, are summarized. By focusing on changes in state functions, all results apply as readily to irreversible processes as to reversible processes. The original global formulation excluded work and heat, which are, in general, path dependent and can be difficult to measure experimentally. However, a particular protocol for defining work and heat relies only on changes in state functions in the surroundings, and this approach allows the reconciliation of work and heat with the philosophy of the global formulation.