Talk:Entropy/Available Energy

message: I have rewritten the first paragraph for the following reasons.  
1. It contained an error, stating
"the entropy in the context of thermodynamics, is a measure of the amount of energy in a physical system that cannot be used to do work."
This is incorrect; entropy is in no sense a measure of energy.  A system can have high energy and low entropy (such as a set of bar magnets all lined up opposite to a magnetic field) or low energy and low entropy (such as a set of bar magnets all lined up in the same direction as a magnetic field). In both cases, you know the entropy is low, because the bar magnets are all lined up in a very organized fashion.  However, you know that the bar magnets lined up opposite to the magnetic field have higher energy, because you could get work out by releasing the magnets from that position.
2.  Because entropy is such an abstract concept, it is difficult to grasp it intuitively without a lot of experience (just as energy would be a difficult concept to grasp if we didn't talk about it all the time in daily life).  However, I think the popular confusion over the concept is exacerbated by the fact that two different definitions are given, and they seem quite different -- because they are.  I hope that my version of the new paragraph has better explained the relationship between the two definitions.
67.186.28.212 13:02, 23 August 2005 (UTC)
replies: text: Entropy is not the quantity of heat; heat is the quantity of heat!  Entropy is defined (in the clausius definition) as heat transfer divided by temperature, hence is not the same as heat.  Furthermore, the unit of heat is joules, and the unit of entropy is joules (or joule, as you like) per kelvin, and thus they cannot measure the same thing. 67.186.28.212 23:56, 21 September 2005 (UTC)

text: The bad design of SI is irrelevant to Wikipedia.  Wikipedia's purpose is to report, not to present original research. 67.186.28.212 23:56, 21 September 2005 (UTC)

text: You are correct in finding an analogy between voltage and temperature:  they are both potentials, in a sense.  I have never heard the term "quality" used to describe a potential, nor can I find this usage anywhere on the net ("quality of electricity" is is used on the net to talk about how steady and environmentally friendly the power supply is, but I cannot find it used to describe electric potential).  Can you cite a peer-reviewed source to justify your usage of the term quality? 67.186.28.212 23:56, 21 September 2005 (UTC)
replies: text: The present introduction states: The entropy can also be understood as the "quality" of heat flowing between two bodies. So here you find the word "quality". I object to this use, however. It is a misunderstanding. I wrote the alternative introduction which nobody liked, but the idea is this. The money (dE) you pay for buying some stuff is the product of the price (T) and the amount (dS). dE=TdS. The amount is the quantity and the price reflects the quality. The analogy is that the energy (dE) you receive from a hot body is the product of the temperature (T) of that body, and the emitted entropy (dS). So temperature is a quality and entropy is a quantity. It is better that saying that entropy is quality, which is the present sad state of affairs.   Bo Jacoby 14:14, 6 October 2005 (UTC)

text: Heat is not the same as energy, so you cannot substitute E for Q.  In the notation you propose, for instance, the first law of thermodynamics would be expressed dE=dE-dW, which is clearly nonsense (whereas the usual notation dE=dQ-dW shows the difference between dE and dQ very precisely). 67.186.28.212 12:00, 21 September 2005 (UTC)
thread_title:  First paragraph rewritten. 

message: I recently edited this page to include the ideas of free energy. However the changes were reverted. Is it not true that entropy is related to "trapped energy" or energy that is not free energy? The product given at the top of the page, S*TR is supposed to be the energy "unavailable to do work" this *is* the energy that isn't free energy. Entropy is a very misunderstood topic and gave me hell for trouble in chemistry - disorder is an awful way to describe entropy because it leads to so much confusion. In any case, I believe it is important to drive home that entropy is *not* disorganization - but is directly related to the energy in a system, namely the trapped energy.  Please discuss the addition of the concept of free energy to this article. 
Fresheneesz 20:16, 20 November 2005 (UTC)
replies: text: Well, I didn't do the reverting, but I think maybe a short section on the subject would be better. Free energy when precisely defined is not an intuitively obvious concept, so references to it seem cryptic to the less informed. PAR 22:11, 20 November 2005 (UTC)

text: Should it go in the free energy article, or the individual Helmholtz free energy and Gibbs free energy articles? PAR 23:11, 20 November 2005 (UTC)
replies: text: I think it should go in this article - after all, it would be about entropy. Saying something like "entropy is closely related to the energy in a system that is not free energy" belongs in the artcle about entropy, not free energy. 68.6.112.70 23:25, 20 November 2005 (UTC)
thread_title: Entropy and free energy

message: The second definition listed says "a measure of disorder in the universe or of the availability of the energy in a system to do work".
Can anybody verify if that is an accurate transcription from the original source, Gribbin's Q Is for Quantum: An Encyclopedia of Particle Physics?
I see it as potentially confusing that it describes entropy as a measure of the availability of energy to do work. Whilst it's probably not strictly incorrect, it would be less confusing to say it is a measure of the unavailability rather than of availability - consistent with saying it is a measure of disorder rather than of order. Alternatively point out that to the extent that entropy is a measure of availability of energy, it is an inverse measure rather than a direct measure.
Can anyone verify the accuracy of the transcription from the source? and if it is accurate, then is it a useful definition?
Mimiselfani (talk) 00:36, 5 February 2014 (UTC)
thread_title:  Standard Textbook Definitions