(559e) How to Teach Best a Basic Understanding of Molecular Interactions and Fluid Phase Thermodynamics

A basic understanding of the interactions of molecules and the resulting fluid phase thermodynamics is essential for practicing good chemical engineering. Nevertheless, it is not so simple to teach such understanding to students. Most simple concepts of polarity and dispersion are not able to explain the problems faced in modern chemical engineering. Group contribution methods are just frameworks of numbers, which do not provide a qualitative understanding of the molecules and their interactions, and molecular modelling also is too indirect and to slow for being useful in a chemical engineering course.

Being based on quantum chemistry, the COSMO-RS method provides vivid graphical pictures of the surface polarity of molecules, making use of the polarization charge density σ of the molecules virtually swimming in a conductor. The electrostatic and hydrogen bond interactions of molecules, as well hydrophobic interactions are quantified based on this surface polarity by simple expressions. As a result the interactions of the molecular surfaces can be easily and intuitively comprehended and students can simply understand why some molecules like each others and others do not, and why it gets warm when you mix acetone and chloroform. The methods leads straight to chemical potentials and activity coefficients, and hence to the entire fluid phase thermodynamics of pure liquids and mixtures.

Using the free educational version of the COSMOtherm program, the students can start to play around with ~300 diverse molecules, check mutual activity coefficients and binary phase diagrams, and do many other educative examples and exercises. They will keep in mind fluid phase thermodynamics as a vivid and colorful discipline.