Why does the physical state of a substance primarily depend on its temperature?

  1. Let me know if i am correct here. Temperature is just the amount of energy associated with that particle or molecule? So why does that determine if it is solid, liquid, or gas? Why doesnt water turn into ice at room temperature when you compress it into itself enough? Like in star wars when they are trapped in the garbage shoot and the walls are caving in (haha), but coming from every direction and squeezing a sample of water, or anything, into itself. Wouldnt the h2o particles eventually become close enough to eachother to become a solid?
  2. jcsd
  3. mfb

    Staff: Mentor

    It does. But you need a really high pressure for that.
  4. Last edited by a moderator: Sep 25, 2014
  5. Correct me if I'm wrong, but I don't think you can compress liquid water into a solid, but just because solid water is LESS dense than liquid water. If water was "normal", you would be able to do it.
  6. mfb

    Staff: Mentor

    That is true at atmospheric pressure, but not for higher pressures. See the phase diagram at Wikipedia, for example.
  7. Most solids are crystalline, with very ordered structure that represents a lowest energy configuration. It doesn't change shape because of that.
    I don't think that if you could compress a liquid enough it would ever form a crystalline solid. You'd just have a very, very dense liquid that still flows.
    The question is how do you define 'solid'?

    Other solids are glasses, which are very viscous, slow flowing liquids. You might make something like that - but can you call it a solid?
  8. Vanadium 50

    Vanadium 50 18,482
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    You can compress water into a solid. It happens just over 1 GPa at room temperature. I believe the crystalline form is tetragonal rather than the hexagonal that we are used to.
  9. mfb

    Staff: Mentor

    Glasses are solid materials. They are not liquids, which is a common misconception.
    If you want long enough, every solid material with finite temperature will have some re-ordering of the atoms. But the typical timescale is so long that this is not relevant.

    Well, it does (at least in general). You press the atoms into some dense structure.
  10. The common misconception is the 'proof' of glazing glass flow by observation of blown glass windows, not the fact that many glass-like materials exhibit flow, particularly thermoplastics, various resins and rubbers.
    The question is as to exactly when very slow movement becomes no movement.
  11. Surely a solid has a(n attempt at) a regular crystal structure or arrangement of molecules.

    Fluids and glasses do not, as do other amorphous states of matter.

    Chemists and physicists also differ in their interpretation of the word 'state of matter', recognising many more than do physicists.
  12. Vanadium 50

    Vanadium 50 18,482
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    I think we've answered the OP's question. Other things besides temperature matter. Pressure. Temperature history (glass vs. quartz). Pressure history (graphite vs. diamond)
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