# Entropy: A Guide for the Perplexed

```On 24.01.2012 22:56 meekerdb said the following:

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``` 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,

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I have started reading the pdf. A few comments to section 2 Entropy in thermodynamics.
```
The authors seem to be sloppy.

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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."
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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.
```
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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."
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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.
```
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3) p.3(117). "If we now restrict attention to adiathermal processes (i.e. ones in which temperature is constant),"
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According to Eq 4 that they discuss they mean an adiabatic process where temperature is not constant.
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However, at the end of this small section they write

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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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