Perturbations of Thermodynamic State Functions

Because small changes in thermodynamic quantities will play a central role in much of the development of thermodynamics, the key concepts are introduced in this short chapter. The First Law (conservation of energy) can be expressed simply in terms of infinitesimal quantities: a small change in the energy of a system is equal to the heat added plus the work done on the system. The theories of statistical mechanics and thermodynamics deal with the same physical phenomena. Exact and inexact differentials are defined, along with the important concept of an integrating factor that relates them. The useful equation relating small changes in heat to corresponding changes in entropy is derived.