Is change of phase always reversible?

In summary, the conversation discusses the concept of irreversibility and equilibrium in various examples, such as a thermosetting polymer and the different allotropes of carbon. There is also a mention of the qualifier of time when considering these processes. The conversation concludes with the idea that some phase changes may not be reversible under certain conditions.
  • #1
trelek2
88
0
If not please give me an example. I can't think of any... I also didn't come across any on the Internet...
 
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  • #2
The only example that comes to mind is that of a thermosetting polymer.
 
  • #3
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'?
 
  • #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
 

1. What is a phase change?

A phase change, also known as a physical change, is the transition of a substance from one state of matter to another, such as from a solid to a liquid or from a liquid to a gas.

2. Is change of phase always reversible?

No, change of phase is not always reversible. It depends on the conditions in which the phase change occurs. Some phase changes, such as melting and freezing, are reversible, while others, such as evaporation and condensation, are not.

3. What factors affect the reversibility of a phase change?

The factors that affect the reversibility of a phase change include temperature, pressure, and the nature of the substance itself. For example, increasing the temperature and pressure can make a phase change irreversible, while using a substance with strong intermolecular forces can make a phase change more reversible.

4. Why is the reversibility of a phase change important?

The reversibility of a phase change is important because it affects the behavior and properties of substances. For example, substances with reversible phase changes can be used in technologies such as refrigeration and air conditioning, while substances with irreversible phase changes can be used to store and release energy.

5. Can a phase change be both reversible and irreversible?

Yes, a phase change can be both reversible and irreversible depending on the specific conditions. For example, melting can be reversible if a solid is heated slowly and evenly, but it can also be irreversible if the solid is heated quickly and unevenly. Similarly, condensation can be reversible if a gas is cooled slowly and evenly, but it can also be irreversible if the gas is cooled quickly and unevenly.

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