Entropy ~ a measure of the disorder of a

system.

A state of high order = low probability

A state of low order = high probability

In an irreversible process, the

universe moves from a state of low

probability to a state of higher

probability.

We will illustrate the concepts by

considering the free expansion of a gas

from volume Vi to volume Vf.

The gas always expands to fill the

available space. It never spontaneously

compresses itself back into the original

volume.

First, two definitions:

Microstate: a description of a system that

specifies the properties (position

and/or momentum, etc.) of each

individual particle.

Macrostate: a more generalized

description of the system; it can be in

terms of macroscopic quantities, such

as P and V, or it can be in terms of the

number of particles whose properties

fall within a given range.

In general, each macrostate contains a

large number of microstates.

An example: Imagine a gas consisting of

just 2 molecules. We want to consider

whether the molecules are in the left or

right half of the container.

See full article here

http://www.pa.msu.edu/courses/2005spring/PHY215/phy215wk4.pdf

## Friday, 14 January 2011

Subscribe to:
Post Comments (Atom)

## 0 comments:

Post a Comment