Statistical mechanics can be studied by visualizing an ensemble, which
is an imaginary set of many replicas of the physical system.
In the microcanonical ensemble, all replicas in the ensemble have the
same energy. The treatment of dilute gases in Chapters 25 and 26 is
equivalent to using the microcanonical ensemble to represent that system.
In the canonical ensemble, all replicas in the ensemble have the same
temperature. Use of this ensemble provides an alternative approach to the
statistical mechanics of dilute gases, and results in the same formulas for
thermodynamic variables for dilute gases as in Chapter 26.
Statistical mechanics can be based on classical mechanics instead of on
quantum mechanics, and this approach is useful in the discussion of
nonideal gases and liquids.
