Re: Why do we care about heat?

[Jim Green <JMGreen@SISNA.COM>]

> David Bowman may jump up and down and disagree with what I'm
> about to say, but the classical meaning of entropy is the one
> which is fundamental here. One can certainly prove that the
> Boltzmann interpretation set in a quantum mechanical frame is
> also correct, but the first applications of the concept were
> to engineering and chemical problems. Solution of such problems
> relies heavily on the distinction between heat and work in
> ideal models.

Yes, he may, Leigh, but David was talking about non-reversible
processes.  I essentailly agree with what you say above, but I am left
wondering how one separates "heat" and "work" in an irreversible
process.  It seems to me that some of the "work/heat" goes into W and some
into Q -- the fraction which contributes to the change in entropy.

I clearly agree that the difference has nothing to do with
temperature.  For example, in the Joule experiments, not all of the effort
of the crank goes into entropy change, but some does.  Maybe I should think
about that statement further. Hummm.

The only part of "heat/work" that goes into W does NOT change the
entropy.  The classical example is the reversible piston in a
cylinder.  However, if I beat the piston down with a 4 tom rock (I think
that I could just barely do that), _some_ work is done -- but not all.

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen