 
Summary: Statistical Mechanics
and
its applications
Dr A. Alavi
Part II Chemistry
20072008
1
I. INTRODUCTION
Statistical Mechanics is concerned with how to describe the behaviour of systems
containing large numbers of particles. Its remit is to provide the theoretical appara
tus to analyse the equilibrium properties of such systems in terms of the underlying
microscopic interactions between the particles. It is common experience (and indeed
experimentally verifiable) that the properties of systems containing very large numbers
of particles depend only on the specification of a few macroscopic parameters such as
total (internal) energy E, temperature T, volume V , pressure P, density , etc. On
the other hand, a detailed description of the microscopic state of a system requires
knowledge of a huge number (on the order of Avogadro's number) of rapidly fluctu
ating variables, such as the positions and momenta of each particle. The measurable
macroscopic properties should be obtainable via an appropriate averaging over the mi
crostates, and how this is done, as well as its theoretical justification, is the subject of
