John Hagen (California Polytechnic State University, USA)
Molecular structure determines physical and chemical properties; this is a central paradigm of chemistry. An accurate calculation of these properties requires the use of statistical mechanics, which students do not learn until their third or fourth year of undergraduate study, and detailed knowledge of the quantum states of the system. We have developed a physical chemistry experiment which emphasizes the connection between molecular structure and physical properties, but does not require any knowledge of statistical mechanics. In this experiment, students use multiple linear regression to construct a quantitative model that predicts the entropy of melting. This model is based on three parameters which quantify molecular size, flexibility, and symmetry. Students use their model to predict the melting entropy of two compounds, and then measure the melting entropy experimentally using DSC. We have used this experiment for several quarters in our physical chemistry lab course.