On 24.01.2012 22:56 meekerdb said the following:
In thinking about how to answer this I came across an excellent paper
by Roman Frigg and Charlotte Werndl
http://www.romanfrigg.org/writings/EntropyGuide.pdf which explicates
the relation more comprehensively than I could and which also gives
some historical background and extensions: specifically look at
section 4.
Brent
Brent,
I have started reading the pdf. A few comments to section 2 Entropy in
thermodynamics.
The authors seem to be sloppy.
1) p. 2 (116). "If we consider a cyclical process—a process in which the
beginning and the end state are the same — a reversible process leaves
the system and its surroundings unchanged."
This is wrong, as one runs the Carnot cycle reversibly, then the heat
will be converted to work (or vice versa) and there will be changes in
the surroundings. They probably mean that if one runs the Carnot cycle
reversibly twice, first in one direction and then in the opposite, then
the surrounding will be unchanged.
2) p. 2(116). "We can then assign an absolute entropy value to every
state of the system by choosing one particular state A (we can choose
any state we please!) as the reference point."
They misuse the conventional terminology. The absolute entropy is
defined by the Third Law and they just want employ S instead of Del S.
It is pretty dangerous, as when one changes the working body in the
Carnot cycle, then such a notation will lead to a catastrophe.
3) p.3(117). "If we now restrict attention to adiathermal processes
(i.e. ones in which temperature is constant),"
According to Eq 4 that they discuss they mean an adiabatic process where
temperature is not constant.
However, at the end of this small section they write
p. 3(117). "S_TD has no intuitive interpretation as a measure of
disorder, disorganization, or randomness (as is often claimed). In fact
such considerations have no place in TD."
I completely agree with that, so I am going to read further.
Evgenii
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