Physics colloquium set for Feb. 23 A physics colloquium is set for 4 p.m. Friday, Feb. 23, in 211 Witmer Hall. Evguenii Kozliak (chemistry) will address "Positional Entropy: Its Significance, Limits of Application, and Relationship to Thermodynamics." Coffee and cookies will be served at 3:30 p.m. in 215 Witmer Hall. Detailed analysis of translational entropy (e.g., the entropy change in ideal gas expansion) as well as the entropy of mixing and residual entropy in crystals shows that these types of positional entropy and of thermal entropy yield identical numerical values for S. However, this is the case only when the system’s “dimensionless” energy gaps (/kT) between quantized energy levels are minimized by temperature to virtually infinitesimal values so that the spreading of energy in a system’s change becomes quasi-classical in nature. For instance, four different approaches to residual entropy (the entropy remaining in crystals comprised of non-symmetric molecules like CO, N2O, FClO3, and H2O as temperatures approach 0 K) based on combinatorics, thermodynamics, mixing, or statistical mechanics/probabilities yield the same numerical values. Considering the combinatorics of mixing, the translational partition function, and characteristic temperature leads to the conclusion that positional entropy calculations are significant because of their fundamental connection to the process of random dispersal of energy in a system. In turn, the use of positional entropy serves as an essential limiting factor for thermal calculations whenever the quantum molecular (wavepacket) size affects the number of microstates in a system. For further information, contact Kozliak at the Department of Chemistry, University of North Dakota, Grand Forks, ND 58202-9024 ekozliak@chem.und.edu -- Connie Cicha, Administrative Secretary, Physics, connie_cicha@und.nodak.edu, 701-777-2911