Exploring Thermodynamics Using Non-Traditional Systems: Elastomers and DNA

Traditional undergraduate physical chemistry courses focus much of their efforts on matter in the gas phase. While a useful approach, the scarcity of applications of the first and second laws of thermodynamics to solids and liquids can leave students with the impression that thermodynamics is only applicable to substances in the gas phase. In this worksheet thermodynamic analysis is applied to elastomers. We begin with the concept of an equation of state and work through several examples analogous to the ideal gas law. The approach used here follows closely the work of B. Smith1,2 and J. E. Mark.3 The analysis is extended to DNA stretching data to illustrate even wider applicability of thermodynamic concepts and tools. Mathcad is particularly useful for elastomer and DNA analysis because experimental data for these systems are more complex and generally require more sophisticated mathematical treatment than their gas phase counterparts. This document can be used anytime after the first and second laws of thermodynamics have been applied to gases. It is most suitable for physical chemistry but may be used in biophysical courses as well. Introduction: The goal of this document is to provide students with an application of thermodynamics concepts to systems beyond those traditionally taught in undergraduate thermodynamics courses. The specific systems used in this work are elastomers and DNA. The worksheet can be used anytime after the First and Second Laws of Thermodynamics but does assume that the student has already seen application of these laws to gas phase systems. The worksheet relies on the use of data taken directly from the literature and requires the use of several Mathcad functions including, importing data, the coding environment, and symbolic mathematical operation. Specific objectives include: