CHEMICAL PHYSICS SEMINAR AND PIZZZA
"Molecular Thermodynamics Visualized"
Texas A\&M University
Classical thermodynamics, developed in the 19th century, dealt solely
with macroscopic properties of matter. Quantum statistical mechanics
triumphantly provided means to evaluate all thermodynamic quantities from
molecular properties, via the partition function. This route to
thermodynamics has proved extremely useful, especially for gas phase
processes. As usually formulated, however, the partition function is not
easily visualized. Moreover, applications often involve a ratio of the
partition functions for two molecules having several atoms or groups in
common. The contributions of many of the degrees of freedom associated
with the common groups then tend to cancel, but this does not find natural
expression in the usual formulation. We present an unorthodox form of the
partition function for a polyatomic molecule that deserves to be better
known. This form has, for each atom, a factor that corresponds to free
translational motion of the atom within an effective volume defined by the
average vibrational amplitudes of the atoms and the geometrical
configuration of the neighboring atoms. When treating chemical reactions,
in many cases the only volume elements that do not cancel to a practical
approximation are those for the atoms in the vicinity of the reaction site.
Thus the important factors, in particular the large volume changes that occur
in transforming vibrational degrees of freedom into rotational and
translational ones, can be readily visualized.
Tuesday, October 4, 2011
IQSE 578, 11:30 a.m.
Mitchell Physics Building
(Pizza, salad, and soda to be served at 12:30 p.m. outside IQSE 578)
THE INSTITUTE FOR QUANTUM
SCIENCE AND ENGINEERING