#####
Terms

**
Average Value
** -
The Average Value of a Property *A* is the value expected if the
measurement were taken on every system in the ensemble and averaged, and
is written as < *A* >.

**
Closed System
** -
A system that maintains a constant number of particles, constant energy,
constant volume, and is free from any change in influences external to
the system, such as an oscillating magnetic field.

**
Conventional
** -
Conventional is a term applied to variables in common uses in the
natural sciences and chemistry, but which in turn are defined in
relation to their fundamental counterparts. We use the term to apply to
*T* and *S*, the conventional temperature and entropy. Compare to
fundamental.

**
Ensemble
** -
A collection of isolated systems, all of which are identical to each
other.

**
Entropy
** -
Entropy, represented by *σ*, is a variable that describes the
randomness of a system and is defined by *σ*(*N*, *U*)âÉálog *g*(*N*, *U*).

**
Fundamental
** -
Fundamental is a term applied to a variable to indicate that it is
naturally defined. We use the term to apply to *σ* and *τ*, the
entropy and temperature. Compare to conventional.

**
Fundamental Assumption
** -
The Fundamental Assumption states that any closed system has an equal
probability to be in any of its possible quantum states.

**
Laws of Thermodynamics
** -
The 4 Laws of Thermodynamics are postulates upon which the study of
thermodynamics historically rested. They exist in numerous formulations
that at times appear unrelated to each other, but can be better
understood from a statistical approach.

**
Multiplicity Function
** -
The Multiplicity Function *g*(*N*, *U*) yields the number of states with the
same values of *N* and *U*.

**
State
** -
The minimal collection of information about a system that is maximally
informative.

**
Temperature
** -
Temperature, represented by

*τ*, is a variable that describes the
thermal agitation of a system and is defined by

= .

#####
Formulae

*P*(

*s*) =

<

*A* > =

*A*(

*s*)

*P*(

*s*)