Is change of phase always reversible?

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Discussion Overview

The discussion revolves around the reversibility of phase changes, exploring whether all phase changes can be reversed or if there are exceptions. Participants consider examples from materials science and chemistry, including polymers and carbon allotropes, and discuss the implications of time and conditions on reversibility.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions the generality of phase changes being reversible and requests examples of irreversible changes.
  • Another participant cites thermosetting polymers as an example of an irreversible phase change.
  • A different participant argues that freezing water can be seen as irreversible under certain conditions, such as maintaining ice below 0°C, and compares this to chemical reactions like concrete setting.
  • One participant introduces the concept of carbon allotropes, suggesting that phase changes involving these forms may not be reversible except under extreme conditions.

Areas of Agreement / Disagreement

Participants express differing views on the reversibility of phase changes, with no consensus reached on whether all phase changes are reversible or if there are definitive examples of irreversible changes.

Contextual Notes

Participants note that the concept of irreversibility may depend on time and specific conditions, indicating that the discussion is nuanced and context-dependent.

trelek2
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If not please give me an example. I can't think of any... I also didn't come across any on the Internet...
 
Science news on Phys.org
The only example that comes to mind is that of a thermosetting polymer.
 
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'?
 
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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