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Pressurization in an enclosed space

  1. Jul 22, 2010 #1
    I have a question regarding the calculation of pressure. Not quite homework but just curious on how things work.

    If I had an enclosed 18 mL (1 mol H2O) container that is indestructible/incompressible filled with water, and boil it so that all the water turns into water vapour, I get 22.4 L of gas, or would the pressure force the gas to remain in liquid form in some way or another, or would I get some combination of the two?

    I'd also assume there'd be a large amount of pressure acting on the container as well due to expansion and whatnot.

    I'm not so sure the Ideal gas law applies in such a situation, as the gas is produced from a liquid and the other values don't quite apply... (as temperature increases, the pressure increases linearly?)

    Am I looking for a case of thermal expansion rather than gaseous expansion, or do both apply? I'm also unsure what else is relevant for this situation.

    Thanks in advance!
  2. jcsd
  3. Jul 23, 2010 #2
    Read up on phases and phase diagrams.

    http://www.chemguide.co.uk/physical/phaseeqia/phasediags.html" [Broken]
    Last edited by a moderator: May 4, 2017
  4. Jul 23, 2010 #3
    The water would not boil. It would reach critical point at about 374 °C where it becomes a supercritical fluid, neither gas nor liquid.
  5. Jul 23, 2010 #4


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    The 22.4L/mol thing is only applicable to standard temperature and pressure. You have neither.

    And yes, if the container does not give, the liquid will become supercritical.
  6. Jul 23, 2010 #5
    Thanks for the prompt replies.

    However, it seems that the premise of my question is faulty.

    I'm more interested in how much pressure would be acting upon the container due to the heating... How would that be calculated?

    Also, how would the behaviour change if say, instead of just increasing the temperature, I changed the internal properties of the water itself, such as converting that container into an electrolytic cell and performing electrolysis (somehow)?
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