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In this course, we are going to develop some machinery for interrelating
the statistical properties of a system containing a very large number of
particles, via a
statistical treatment of the laws of atomic or molecular motion.
It turns out that once we have developed this machinery, we can obtain some very
general results which do not depend on the exact details of the statistical
treatment.
These results can be described without
reference to the underlying statistical nature of the system, but their
validity depends ultimately on statistical arguments. They
take the form of general statements regarding heat and work, and are
usually referred to as *classical thermodynamics*, or just
*thermodynamics*,
for short. Historically, classical thermodynamics was the first sort of
thermodynamics to be discovered. In fact, for many years
the laws of classical
thermodynamics seemed rather mysterious, because their statistical
justification had yet to be discovered.
The strength of classical
thermodynamics is its great *generality*,
which comes about because it does not
depend on any detailed assumptions about the statistical properties
of the system under investigation. This generality
is also the principle weakness of classical thermodynamics. Only a relatively
few statements can be made on such general grounds, so many interesting
properties of the system remain outside the scope of this theory.
If we go beyond classical thermodynamics, and start to investigate the
statistical machinery which underpins it, then we get all of the
results of classical
thermodynamics, plus a large number of other results which enable the
macroscopic parameters of the system to be calculated from a knowledge
of its microscopic constituents. This approach is known as
*statistical thermodynamics*, and is extremely powerful.
The only drawback
is that the further we delve inside the statistical machinery
of thermodynamics, the harder it becomes to perform the necessary
calculations.

Note
that both classical and statistical thermodynamics are
only valid for systems in *equilibrium*.
If the system is not in equilibrium
then the problem becomes considerably more difficult.
In fact, the thermodynamics of
non-equilibrium systems, which
is generally called *irreversible thermodynamics*,
is a graduate level subject.

** Next:** Classical and quantum approaches
** Up:** Introduction
** Previous:** Microscopic and macroscopic systems
Richard Fitzpatrick
2006-02-02