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B Correct statement of 2nd law of thermodynamics?

  1. Dec 4, 2017 #1
    Thermodynamics is stated in different ways. E.g.
    In isolated systems entropy never decreases
    Heat never spontaneously pass from colder to warmer body
    Total energy quality decreases in all processes.
    Energy disperses

    But what is it exactly? What is the correct description of the 2nd law of themodynamics?
  2. jcsd
  3. Dec 4, 2017 #2


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  4. Dec 4, 2017 #3

    Mister T

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    Those two statements are logically equivalent. (That is, if you assume either one as a premise you can show that the other follows as a consequence.)

    They are each statements of the 2nd Law. There is no way to say that either one is more or less correct than the other. And there are several other logically equivalent statements that are also equally correct statements of the 2nd Law.

    These, on the other hand, seem more descriptive. They are perhaps consequences of the 2nd Law? But I wouldn't refer to them as statements of the 2nd Law.

  5. Dec 4, 2017 #4
    Would you like to see a mathematical statement of the 2nd Law of Thermodynamics?
  6. Dec 5, 2017 #5
    2nd law of Thermodynamics says that total entropy never decreases in a closed system (in the universe).

    In this link entropy is explained as "nr of possible arrangements": https://aatishb.com/entropy/
    If you take a quick look at the link, according to the link above, more energy quants in a body can have more nr. of possible arrangements. Less energy quants in a body can have less nr. of possible arrangements.
    Then that means any system that's cooling down (e.g. hot coffee cooling down) has a decreasing entropy, because the systems' energy quants decreases?
  7. Dec 5, 2017 #6


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    ... plus the "quants" increasing in the reservoir given up by the "coffee cooling." At least as much for a "reversible" process, zero net change, and for any "real process" occurring in less than infinite time, a greater than zero change.
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