CHEM 350 Lecture 7, 8, and 9, January 18, 20, and 22, 2010
Introduction to Statistical Mechanics.
There are two general approaches to the description of physical systems:
: large units of matter; units mol, mmol, etc.
: physical system examined in terms of individual molecules and their motions.
We can use either
(a) Classical mechanics: specify values of
, etc., for each molecule in the
each complete set of such values makes up a microstate.
(b) Quantum mechanics: specify wave function
) for each molecule in the sam-
ple, together with the appropriate quantum numbers characterizing the MICROSTATE.
It is appealing to attempt to explain or interpret macroscopic behaviour in terms of laws gov-
erning the microscopic constituents, BUT how do we work out the detailed behaviour of so many
In principle, this problem is intractable from such a point of view. We need a new branch of
laws of mechanics and electromagnetism, which are concerned with motions and
properties of atoms, molecules, etc.
: idea of arriving at a detailed description of the particle motions.