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I have read the Karlsruhe physics online courses and the authors are adamant that entropy is just what people call heat in daily life, not to be confused with heat as transfer of energy.

Do you think that this statement is true?

Disclaimer: I don't advocate this theory. I want to ask why it is wrong or correct

Michael
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  • Note: Some time ago, in a somewhat controversial move, the German Physical Society (DPG) released a report that deems the Karlsruher Physikkurs (KPK) partly confusing, partly wrong, and unfit for teaching physics. – ACuriousMind Jan 28 '17 at 14:17
  • @ACuriousMind I know that a controversy exists. I only ask about what other people may think. I don't care about DPG. What is your opinion on the essence of their arguments? All the rest are gossip –  Jan 28 '17 at 15:30
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    This issue goes back to Carnot himself and many historians of science have claim that what Carnot was talking about was indeed entropy and not "heat" because he was discussing some kind of conserved quantity that changes its ability to perform work proportionally to the temperature at which it is absorbed. The conserved quantity is entropy in a reversible process and it is the ratio of absorbed heat to temperature. Moreover that entropy is indeed transferred from/to the environment and it is conserved unlike "heat" that disappears in the process. – hyportnex Jan 28 '17 at 21:31

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No, it's not true. Entropy and heat are very closely related, but it's confusing and wrong to say they're the same. I suppose you could say, very informally and with some hand-waving about units, that what people informally call heat is one form of entropy. However, there are also other forms of entropy that are not heat.

As an example, consider what happens when you stretch an elastic band out for a while and then let it contract again. When the elastic relaxes, it cools down. Why? Because the relaxed rubber has a greater entropy than in the stretched state (follow the link for more details of why), and this means that entropy in the form of heat can be converted into entropy in the form of molecular configurations, allowing the amount of heat to decrease while the total entropy stays more or less the same.

It should be stressed though, that this is all really informal language and not quite correct. (In particular, there is not really such a thing as "the amount of heat".) If you want to learn the subject properly there isn't really any substitute for learning the proper language that physicists use to describe thermodynamics, and it's important to keep in mind that this way of thinking about it isn't quite correct.

Community
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N. Virgo
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    One should mention (see also my comment to the question) that OP seems to draw from an unorthodox source, namely the Karlsruher Physikkurs [German Wiki link]. There's a sizable controversy between its proponents and the experts appointed by the DPG about whether the statements it teaches are wrong or merely on the level of "alternative definitions/interpretations". – ACuriousMind Jan 28 '17 at 14:25
  • @ACuriousMind thank you for the comment, that's helpful to know. – N. Virgo Jan 28 '17 at 14:46
  • Your answer was useful, who cares about DPG? –  Jan 28 '17 at 15:33
  • If the relaxed rubber has a greater entropy than the stretched one, where does the entropy in the band go when you stretch it? It must go into the air right? And when you relax it, is the higher entropy in the band generated or is it taken from the air? – Michael Feb 07 '24 at 07:29
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In thermodynamics, heat is defined as the process of transfer of energy.

So you can't ask, how much heat an object has, only how much energy is going in or out of the system during some time period.

The definition of entropy is dependent on the area of physics you are dealing with, in thermodynamics it is defined as $S = k ln \Omega$.

If this looks too maths based for you, read this page Entropy and you might appreciate how straightforward it is, compared to the complications involved in explaining entropy in words.

Entropy is a measure of the number of states a system, such as those in which container of gas might be found in, over a period of time.

The main difference between energy and entropy is that energy is conserved, but entropy is not conserved and will increase over time.

  • Heat is not energy, and while it is always better to use it as a verb (to heat something) and not as a noun, if you insist on using it as a noun then it is much better to consider it as a form of work. – hyportnex Jan 28 '17 at 21:27
  • @hyportnex it's up to me to research deeper, so I won't take up your time with questions. I believe you, the book I use "Intro. To Thermal Physics" by Schroeder, does say P.18 "Heat is defined as a spontaneous flow of energy" and "energy transfered is called heat". But on an earlier TD related question, I used this book as a quote source and was told it was incorrect. I dug deeper and yes, the book was wrong. So, I will finish the book, as it contains a lot of interesting material, then read a more advanced book. Have you a link to recommend? Otherwise I will search. Thanks. –  Jan 28 '17 at 22:17
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    @Counto10 if you wish to think of heat as how Schroeder defines it, that is OK too but note that even then he defines it not as "energy" but rather as "the spontaneous flow of energy", the two are not the same. Energy flow or energy transfer is what work is. A very good article from which I stole the grammatical distinction (verb vs. noun) and one that you may wish to read on the subject is Romer: "Heat is not a noun", Am. J. Phys. 69 (2), February 2001, pp 107-109. Remember heat is not and cannot be contained in anything; a body has no heat, it has energy. – hyportnex Jan 28 '17 at 23:02
  • @hyportnex yes, my head hurt trying to figure out the nuances of those statements. They do sound a touch zenlike to me. But I really just wanted an overall view of the range of TD. But I have QFT as a self study learning goal, so if I get the general picture of TD I will be happy, its one of the many subjects I neglected in tbe past. Thanks for your advice. –  Jan 28 '17 at 23:18
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Entropy, $$\Delta S = \frac QT $$ provides us with a way to state the second law of thermodynamics.

Enthalpy, $$H=U+PV$$ is a quantifier of internal energy such that $P$ and $V$ are the pressure and volume, and $U$ is the internal energy. Enthalpy is an analogue of the first law of thermodynamics $$\Delta U=Q-W$$ applied to the case of constant pressure systems, $$Q=P\Delta V + \Delta U$$ hope this helps.

Infinite Monkey
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You may be talking about enthalpy. Enthalpy in the heat content of a body at constant pressure.

Entropy is just the degree of randomness.

Mitchell
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  • Entropy for sure is not a measure of randomness.Besides, randomness can't be measured –  Jan 28 '17 at 13:16