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Entropy is disorder = outmoded theory?

  1. Jun 27, 2010 #1
    "entropy is disorder" = outmoded theory??

    The wikipedia article I quote below is confusing me. I followed the links to Frank Lambert's website, where he claims that Peter Atkins, in the 8th edition of his Physical Chemistry, has come around to Lambert's idea that entropy is not related to disorder. Could this be true? I would be less surprised to learn that Atkins had become a born-again Christian. However, according to my old-fashioned understanding of entropy, even very improbable things happen occasionally, given a sufficiently huge number of trials. Seriously, I was about to start reading the 7th edition of Atkins Physical Chemistry, but now I'm wondering if I should look for a more reliable author.

    Traditionally, 20th century textbooks have introduced entropy as order and disorder so that it provides "a measurement of the disorder or randomness of a system". It has been argued that ambiguities in the terms used (such as "disorder" and "chaos") contribute to widespread confusion and can hinder comprehension of entropy for most students. A more recent formulation associated with Frank L. Lambert describing entropy as energy dispersal describes entropy as measuring "the spontaneous dispersal of energy — at a specific temperature."

    March 2006
    Atkins' "Physical Chemistry" has been the best selling text worldwide in this subject for many years.* The new 8th edition was published in the US March 16. However, in previous editions Atkins described systems and entropy change in terms of order and disorder or chaos.* Even though he long has used the phrase, "the dispersal of energy", it was confined to an order-disorder view of thermodynamics — for example, to spontaneous changes being "always accompanied by a dispersal of energy into a more disordered state".** (Or "to chaos" in his book "The Second Law".)
    In contrast to the Second Law chapter of the 7th edition, which had some 27 instances of using "order to disorder" as a rationale for change, "disorder" and "disorderly" are mentioned only 3 times in the new 8th edition.* Atkins, with co-author dePaula, now state that their view of entropy "summarized by the Boltzmann formula is consistent with our previous statement [earlier in the chapter, re the dispersal of energy in classical thermodynamics] that the entropy is related to the dispersal of energy.
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  3. Jun 27, 2010 #2
    Re: "entropy is disorder" = outmoded theory??

    How is dispersal of energy an explanation for why a drop of dye disseminates into a glass of water? Isn't there just a certain amount of molecular motion due to heat-energy, which causes particles to tend to move around randomly such that the dye particles are likely to randomly traverse the particles of clear water and vice versa? Is that energy dispersion or just expression of energy as molecular motion?
  4. Jun 27, 2010 #3
    Re: "entropy is disorder" = outmoded theory??

    Originators of new ideas are always claiming support from others...who knows what Atkins believes and whether that REALLY meshes with Lambert's idea.

    I would not disregard a proven text because of such a claim. I've never even heard of "dispersal" of energy nor do I know whether Atkins/Lambert agree on what it is.

    Entropy is a difficult enough concept that if someone has a better explanation, I'd like to read it.
  5. Jun 27, 2010 #4
    Re: "entropy is disorder" = outmoded theory??

    Energy "dispersal" is a generally logical concept. It is what happens when a cue-ball breaks a triangle of billiard balls. If you have a room of 40 degree air and you make a fire, convection is the result of high KE among air molecules next to the fire dispersing energy to other molecules they come in contact with. Eventually, the system temperature will reach equilibrium, except the heated air will be pushed up by the denser cool air, which will grow as parts of the warm air disperse their energy through the windows and walls and subsequently sink.

    Dispersal is just a pattern of transfer between high-energy particles and lower-energy ones. It's empirical common-sense, no?
  6. Jun 28, 2010 #5
    Re: "entropy is disorder" = outmoded theory??

    Actually entropy has a one-to-one relation to the probability of that particular state being a final state after a "sufficient amount of time" has passed. The relation is a very steep exponential so that slightly higher entropy is extraordinarily favoured by probability.
    But still lower entropy states do have a finite probability and will occur.
  7. Jun 28, 2010 #6

    Andy Resnick

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    Re: "entropy is disorder" = outmoded theory??

    There are several potentially confusing things in those sites. First, entropy relates to a given state, and so cannot be used to describe a process ('dispersal' of energy). Second, there seems to be loose control over discussion of entropy and changes to entropy. Third, 'entropy', like 'energy' is not that well defined outside of quantitative relationships.

    Personally, I see the entropy of a state as that amount of energy unavailable to perform useful work. The free energy is the total amount of energy available to perform useful work.
  8. Jun 28, 2010 #7


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    Re: "entropy is disorder" = outmoded theory??

    I wouldn't say it's an "outmoded theory". It's not a theory and never was. It's just an interpretation that helps explain it. As such it may be an outmoded way of explaining entropy.

    Equating entropy with disorder only makes sense in a few cases. Gas is more 'disordered' than liquid, both are more disordered than a solid. Mixtures are more disordered than pure substances.

    But beyond that, equating entropy with disorder doesn't have much use. Another, more general definition of entropy is "energy not available to perform work". How this relates to entropy being 'disorder' isn't obvious. (In fact, I'd say that once you reconcile these views, that's when you 'get' entropy)
  9. Jun 29, 2010 #8
    Re: "entropy is disorder" = outmoded theory??

    There are relationships between disorder, unavailable energy, and thermodynamic entropy. However, relationships do not appear to me to serve as tight enough explanations about: What is thermodynamic entropy as discovered and defined by Clausius.

    If thermodynamic entropy is a measure of un-usable energy or a measure of disorder then, why are equilibrium conditions necessary to calculate it? In other words: What is the relationship between absorbing and expelling heat under equilibrium conditions, clearly an ideal condition, but, still necessary in the original macroscopic thermodynamic definition, and the amount of heat that leaks away?

    There has already been a very detailed excellent discussion about the development of thermodynamic entropy in another thread. My intention in making this post is only to register an opinion and not to reopen the history of thermodynamic entropy. Even my question is posed without expecting an answer. It is intended to highlight something that I think is of significant importance, and, that I think is passed over in explanations.

  10. Jun 29, 2010 #9
    Re: "entropy is disorder" = outmoded theory??

    Heat can only "leak away" as long as there is something in the system that is not in equilibrium with whatever is leaking the heat.
  11. Jun 29, 2010 #10
    Re: "entropy is disorder" = outmoded theory??

    Nevertheless, that is a condition of the original definition. Is your point that the original definition is inherently mistaken and can therefore be disregarded in favor of other definitions that do not have to take into account that which Clausius discovered?
  12. Jun 29, 2010 #11
    Re: "entropy is disorder" = outmoded theory??

    entropy as a measure of disorder has WIDE application....to the evolution of the entire universe, for example, as long as one understands the effects of gravity on entropy disorder.

    Entropy is a subset of information theory. and is extremely useful in understanding black hole event horizons. and is linked to decoherence in quantum mechanics which like entropy lets you know which way time is running. The idea that strings in string theory have entropy goes back to the earliest days of string theory.
    Last edited: Jun 30, 2010
  13. Jun 29, 2010 #12
    Re: "entropy is disorder" = outmoded theory??

    The genealogy and hermeneutics of "the original definition" may be of consequence if your interest is the history of science, but empirical logic makes it clear that heat can't go anywhere unless there is something in disequilibrium with something else. The fact that you define the system in exclusion of the thing that is in disequilibrium with it is a methodological failure to include everything in the system that is influencing the parts of it you are studying.
  14. Jun 29, 2010 #13
    Re: "entropy is disorder" = outmoded theory??

    Clausius defined the system.
  15. Jun 29, 2010 #14
    Re: "entropy is disorder" = outmoded theory??

    I don't know which system you're saying Clausius defined, but I doubt it is any specific system that you have access to study empirically. You have to apply the methodology to test it.
  16. Jun 29, 2010 #15
    Re: "entropy is disorder" = outmoded theory??

    The system is an irreversible carnot cycle.
  17. Jun 29, 2010 #16
    Re: "entropy is disorder" = outmoded theory??

    In other words, theoretical rather than empirical.
  18. Jun 29, 2010 #17
    Re: "entropy is disorder" = outmoded theory??

    Of course. So is a frictionless surface. Still, the question remains. Is your point that the original definition is inherently mistaken and can therefore be disregarded in favor of other definitions that do not have to take into account that which Clausius discovered? This is not my work. Clausius discovered thermodynamic entropy.
  19. Jun 29, 2010 #18
    Re: "entropy is disorder" = outmoded theory??

    My point is that if heat is moving in a system that is "in equilibrium," then there is some element that is receiving the heat, which means that the system is not in equilibrium, probably because it has been defined in exclusion of whatever it is that is receiving the heat.
  20. Jun 29, 2010 #19
    Re: "entropy is disorder" = outmoded theory??

    Ok you have made your point. I posted my first message because my opinion is that Clausius' discovery is of fundamental importance and remains unexplained. It was ideal and impractical, but it worked and gave us knowledge of a very important property. For some reason, the conditions that he defined are necessary to correctly calculate thermodynamic entropy. I think it is important to know why. If you disagree, that is fine.

    We have reached a point where you are repeating your message. I understood your message the first time. You are correct in what you say. However, the ideal circumstances can be very closely approximated by having the heat exchanged very very slowly. The use of very very slow actions is common in the derivations of thermodynamic properties since thermodynamics is defined as applying to equilibrium conditions. Temperature is an equilibrium condition, yet we can still make use of the concept of changes in temperature if the process proceeds very very slowly.
  21. Jun 30, 2010 #20
    Re: "entropy is disorder" = outmoded theory??

    The reason some authors may want to disassociate entropy from disorder has nothing to do with a rejection that entropy increase involves mixing unlikely macro-states into statistically more probable macro-states, or uniformity of a system. That remains, just as your old fashion understanding of entropy indicates. The term "disorder" in thermodynamics has an opposite meaning in everyday use, and discussions of this is often misunderstood as somehow rejecting the classical interpretation, which is not the case.

    The "at a specific temperature" qualifier Lambert's definition used refers only to the total temperature of the system in question, not a uniform temperature of that system.
    You can read Lambert's own words here:
    And in J. Chem. Educ., 2002, 79 (2), p 187

    Then there are micro-state issues I find interesting:
    (preprint) http://arxiv.org/abs/1005.1683" [Broken]

    Heat does not have an existence separate from the motion and physical state of the system that defines it. It's an abstraction of the state of things, not itself a substance that flows. Take a tank of of gas with no heat flowing in or out of it, a perfectly enclosed system in thermal equilibrium. Does this mean heat is not moving in this system? No!

    Heat is, at the molecular level, is the kinetic energy of the molecules, 1/2Mv^2, a product of molecular velocity. The only way to stop heat from moving in this system is to stop all molecular motion within the tank relative to the tank. This can NEVER happen without heat escaping the tank. The 2nd law makes no claim that motion eventually stops as entropy increases. So what does "in equilibrium" mean?

    "In equilibrium" merely means that, on average, the temperature is the same everywhere in the tank, such that if you read the temperature at one place in the tank you know the temperature everywhere in the tank. Yet the molecules are still bouncing around trading energy. Thus heat is perpetually moving in a system, whether in equilibrium or not. The 2nd law, entropy, only requires heat in non-equilibrium to evolve toward equilibrium, not stop moving.
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