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Is change of phase always reversible?

  1. Dec 24, 2009 #1
    If not please give me an example. I can't think of any.... I also didn't come across any on the Internet...
     
  2. jcsd
  3. Dec 24, 2009 #2
    The only example that comes to mind is that of a thermosetting polymer.
     
  4. Dec 25, 2009 #3

    Andy Resnick

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    I can't tell what you mean, exactly- clearly, if water freezes and the ice is kept below 0 C, the phase change is irreversible. I wonder if you mean something more like a chemical reaction- when concrete sets for example, it will never revert back to it's dehydrated form... I don't know if it can be ground up and somehow processed back to the way it was.

    Often 'irreversible' and 'equilibrium' must include the qualifier- 'how long do you want to wait'?
     
  5. Dec 25, 2009 #4
    In principle, yes, but carbon for example has 6 or more allotropes, including diamond, buckyballs, nanotunbes, etc. See
    http://en.wikipedia.org/wiki/Allotropes_of_carbon
    So melting or subliming some of these may not be reversible except in extreme conditions.
    Bob S
     
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