Re: entropy

["Richard W. Tarara" <rtarara@saintmarys.edu>]

I'm way out of my depth here, but let me offer the following:

Sears "Thermodynamics" seems to conveniently NEVER gives a verbal
definition of entropy but

Kittel "Thermal Physics" does:  (pgs 46-49)

<skipping a lot>
"This is a definition whose simplicity leaves us breathless:  the entropy
is the logarithm of the number of states accessible to the system."  {Note:
our common entropy S is Boltzman's constant times the quantitiy defined by
Kittel.}

later

"It is said that entropy is a measure of the randomness of a system; this
statement is made precise by the definition (sigma) = log(g).  The more
states that are accessible, the greater the entropy"    {here sigma is
Kittel's entropy and g is the degeneracy of the system}

later yet

"The definition {of entropy} leads to the statement below of what is called
the third law of thermodynamics.  The dignity of a law of nature should not
be conferred on what is essentially a definition.  However, in the early
history of thermal physics the physical significance of the entropy was not
known.  In that period, for example, the author of the article on
thermodynamics in the Encylopaedia Brittannica, 11th ed., wrote that 'The
utility of the conception of entropy...is limited by the fact that id does
not correspond directly to any directly measurable physical property, but
is merely a mathematical function of the definition of absolute
temperature.'  But we know now what physical property entropy measures, and
we know also that entropy is of central importance in thermal physics."

If this is OK with Leigh and the other Thermo-types, then what is the
difference between the number of accessible states of a system and 'a
measure of the disorder (or randomness) of the system'---in practical
terms.

Rick



> On Fri, 22 Nov 1996, Rauber, Joel              Phys wrote:
>
> > Leigh,
> > You wrote
> >
> > > *Perhaps the worst is the association of entropy with disorder. It is
> > > difficult to pry the student loose from this idea later on. I get to
> > > teach thermo next semester; I'll hit this barrier again
> >
> > Could you expand your thoughts on this further; I'd greatly like to
hear 
> > your opinions.  I'm about to talk about entropy in two weeks and would
find 
> > this fascinating.