Thermodynamics—A Model Subject

The teaching of thermodynamics, not to mention the writing of a book on thermodynamics, presents a great challenge for anyone foolhardy enough to undertake it. How to present the subject?—historical or postulational; classical or statistical; macroscopic or microscopic; mathematical or non-mathematical; rigorous or close enough; applications or fundamentals; and so on. Then there is the uncomfortable fact that, as Reiss (1965) points out, one very probably doesn't completely understand the subject. But if teaching thermodynamics presents difficulties, what of the poor student who is subjected to an almost insuperable series of obstacles; everything seems to depend on infinitesimals, on the most unusual and unlikely hypothetical systems, on differentials which may or may not be integrable, and especially on reversible processes which are completely unimaginable and seem to be the key to everything. Somehow out of this mess come concepts and relationships which are very useful in the real world, and it can be argued that in introductory courses the goal should be an ability to use these relationships, not to understand them. At the same time the subject is so profound and esthetically pleasing to scientists that many feel the urge to rhapsodize on it. Lewis and Randall (1923), who wrote one of the more significant books on the subject after Gibbs, likened thermodynamics to a cathedral inspiring solemnity and awe; Einstein wrote that it was the only physical theory of universal content that he was sure would never be overthrown. The profundity of the subject comes from the seemingly universal applicability of its premises and conclusions to some of the most fundamental questions of science, and the elegance from the simplicity and symmetry of its mathematical operations. For example, it is quite amazing to realize that essentially all the geochemical applications discussed in this book involve a single equation, along with a few direct descendants, derived directly from the first and second laws of thermodynamics. It is a considerable challenge to show the meaning of this equation and how to use it. In this text we present the subject as we would have liked to have had it presented to us—with a careful and complete explanation of some fundamental points, a partial or complete neglect of others, a combination of historical, postulational, and statistical approaches as seems appropriate at the moment, and a smattering of applications in geochemistry.