Re: Heating/Work

["Bob Sciamanda" <trebor@velocity.net>]

-----Original Message-----
From: Jim Green <JMGreen@sisna.com>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>
Date: Wednesday, July 22, 1998 9:19 PM
Subject: Heating/Work
> . . .

> As to the meaning of heating and work (I make it a practice not to use
evil
> four letter words) let me add the following:
> The only distinguishing characteristic between heating (an action)  and
> work (an action) is that heating changes the entropy and work does not.
> Thus a system sitting on a hot plate, being played on by a propane
torch,
> having an internal resistor energized by a battery (internal or external
> -- it doesn't matter), being bombarded by high energy particles/photons,
> being in a microwave oven, all are HEATING because they all (I think)
> change the entropy.  A moving piston compressing a gas does NOT change
the
> entropy and therefore does WORK.  (The proof of this is not yet on the
WWW
> page -- I will put it there if there is sufficient interest.)
> > . .
> Jim Green
> JMGreen@sisna.com
> http://users.sisna.com/jmgreen

I think you have a problem using entropy change to distinguish "heating"
from "working" , Jim.
Entropy is a state function - its change is independent of  "path".  A
moving piston irreversibly compressing a thermally insulated gas DOES
change the state and the entropy of the gas.  (It is true that  a
REVERSIBLE, adiabatic process results in zero entropy change of a CLOSED
system.)

Consider that the free expansion (into a vacuum compartment ) of an
isolated gas involves an entropy change with zero "working " or heating"
from the outside.  The state has changed, and so has the entropy, with no
possible correlation to any "working" on the system.

Entropy is determined by the system state.  Working and Heating refer to
the history of specific processes which (among many other "equivalent"
possibilities) led to that state.

-Bob

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor