Traditional undergraduate physical chemistry courses focus much of their efforts on matter in the gas phase. While this is 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 Smith (1, 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. 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 operations.
DNA force length indicator plot. The vertical axis shows force (in piconewtons) required to extend () or contract () the DNA. A structural transition occurs when the force reaches about 60–65 pN for β-DNA in high salt. This structural transition is called the overstretching transition (4)
Literature Cited
Smith, B. Using Rubber-Elastic Material–Ideal Gas Analogies To Teach Introductory Thermodynamics, Part I: Equations of State. J. Chem. Educ.2002,79, 1444–1452.
Smith, B. Using Rubber-Elastic Material–Ideal Gas Analogies To Teach Introductory Thermodynamics, Part II: The Laws of Thermodynamics. J. Chem. Educ.2002,79, 1453–1461.
Mark, J. E. Some Aspects of Rubberlike Elasticity Useful in Teaching Basic Concepts in Physical Chemistry. J. Chem. Educ.2002,79, 1437–1443.
Williams, M. C.; Rouzina, I; Bloomfield, V. A. Thermodynamics of DNA Interactions from Single Molecule Stretching Experiments. Acc. Chem. Res. 2002, 35, 159–166.
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) or contract (
) the DNA. A structural transition occurs when the force reaches about 60–65 pN for β-DNA in high salt. This structural transition is called the overstretching transition 
