9. Gas Kinetic Theory of Entropy

This chapter will attempt to provide a physical understanding of the concept of entropy based on the kinetic theory of gases. Entropy in classical thermodynamics is a mathematical concept that is derived from a closed cycle on a reversible Carnot heat engine. For many students it lacks physical meaning. Most students have a physical understanding of variables like volume, temperature, and pressure. Internal energy and enthalpy are easy to understand, if not intuitive. However, entropy is a bit more difficult. The discussion that follows is an attempt to provide physical insight into the concept of entropy at the introductory level. This discussion closely follows the excellent text “Elements of Statistical Thermodynamics” by L. K. Nash, Dover 2006 [1–4].