Abstract
Thermodynamics is taught in universities and colleges as a part of physical chemistry or general chemistry. It is a basic discipline and is required in later studies when the students specialize in various fields of science and engineering. There are different organizations of thermodynamics courses with respect to how the entropy is introduced: the traditional Carnot-Clausius-Kelvin-Planck approach, the axiomatic Caratheodory approach, the formal approach by Callen, and Boltzmann's statistical definition of entropy and Gibb's statistical mechanics. The author finds the combination of the traditional approach and elementary statistical method the most accessible for students in introductory thermodynamics courses. Based on the belief that the lack of thermal events in our daily experience in which the entropy is conserved lies at the core of the difficulty we have when we try to understand the entropy concept, the author has contrived an experiment for demonstration in thermodynamics courses in which the temperature of an elastic rubber band is measured as it heats and cools in response to elongation and contraction. Reversibility of the temperature change demonstrates the existence of a conserved quantity, other than the energy, in this thermal event. Connection of this experiment with the Carnot cycle and the Boltzmann entropy is made complete by the knowledge of the random structure of rubber polymers.
