198
SYSTEMS COMPOSED OF MOLECULES.
|
(516)
|
or
|
(517)
|
This may be called the probability of the petit ensemble
. The sum of all such probabilities is evidently unity. That is,
|
(518)
|
which agrees with (506).
The average value in the grand ensemble of any quantity , is given by the formula
|
(519)
|
If
is a function of
alone,
i. e., if it has the same value in all systems of any same petit ensemble, the formula reduces to
|
(520)
|
Again, if we write
and
to distinguish averages in the grand and petit ensembles, we shall have
|
(521)
|
In this chapter, in which we are treating of grand ensembles, will always denote the average for a grand ensemble. In the preceding chapters, has always denoted the average for a petit ensemble.