[FRIAM] Entropy RE-redux

[Nicholas Thompson]

Dear Colleagues,
I am trying to "design" the simplest sort of phenomenon that demands the
concept of entropy.  My first description left many ambiguities which I
have attempted to correct in this revision.  Unfortunately, the revision
has gotten horribly long.  Still, I am hoping that at least a few of you
-- as you love me -- will respond.  Here is the prompt.

Our goal is to juxtapose two bodies of air, of equal temperature  and
volume but different histories  to see which can exert the most pressure.
Thus we hope to separate the effects of temperature, per se, from the
effects of how that temperature was arrived at.   We start with a single
cylinder of air at one bar (roughly  sea-level pressure) and 50 degrees C,
which contains three slidable/peggable dividers.  One is installed at the
exact middle of the cylinder, the other two at opposite ends.  All motions
of the sliders will be quasi- static (infinitely) slow).  The cylinders and
the sliders are designed to be adiabatic—no heat or mass can pass through
them—except in the following two respects.  Just  to the right of the
central slider are installed two ports, one through which air may be
admitted or released and a second through which heat may enter or depart
through conduction.     These ports will always  be assumed to be
adiabatically sealed unless explicitly described otherwise.  Finally, on
either side of the central slider is installed a temperature sensor so that
we may know the temperature within the two chambers.

With this equipment in hand, we begin the preparation of the two juxtaposed
chambers.  On the left, we push in the slider until the left chamber
reaches a temperature of 20 degrees C. and we peg it there.   We measure
the distance from the left slider to the central slider  . Now, we open the
heat and air ports on the right side of the central slider and  we push in
the right slider until it is the same distance from the central slider as
the left slider is on the other side.  (Thus we have guaranteed that the
volume of the two adjacent chambers is the same)    Now we close the air
port.   Through the still open heat port we admit just enough heat  to
bring the temperature up to 20 degrees C. and then we seal it.  So now we
have, as planned, two adjacent chambers, of equal temperature and volume.  Now
we unpeg the central divider.  Which way, if any, does it move and why?


-- 
nick
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