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Gas pressure

  1. Nov 29, 2014 #1
    i wonder if "gas pressure > out pressure" this can be possible. if so how?
     
  2. jcsd
  3. Nov 29, 2014 #2
    Ahem. What?
     
  4. Nov 29, 2014 #3

    Danger

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    Gold Member

    Copy that...
     
  5. Nov 30, 2014 #4
    sorry for bad translation. that was all i can do
     
  6. Nov 30, 2014 #5
    I do not understand the question in #1. Rephrase it.
     
  7. Nov 30, 2014 #6

    russ_watters

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    Staff: Mentor

    It is not a translation problem, it is a description problem. You only gave us part of one sentence! Please write a much longer description of the problem and translate that.
     
  8. Dec 1, 2014 #7
    as we know when the gas pressure of a liquad is equal with the outside pressure, liquid starts to boil. im asking that if the gas pressure of a liquid can be "bigger" than the outside pressure.
    and yeah its both description and translation problem
     
  9. Dec 1, 2014 #8
    No, that is not true. At every free air-water interface (every lake, river, sea) the pressures are exactly equal. Is there any boiling?
     
  10. Dec 1, 2014 #9

    russ_watters

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    Staff: Mentor

    That would be a translation/comprehension issue: tjukzzhd is referring to vapor pressure.

    The answer is no, the saturation pressure in the liquid cannot be higher than the vapor pressure outside of it. If it tries to be, the water just instantly flashes to steam (this happens when hot, pressurized water flows through a valve or nozzle, lowering its pressure).
     
  11. Dec 1, 2014 #10
    I am not sure I follow this. You said the question was about vapor. If vapor pressure exceeds ambient pressure, then it just expands, possibly part of it condensing or even solidifying in the process.

    But then you gave an example involving a liquid, not vapor. What are we really discussing here?
     
  12. Dec 1, 2014 #11

    russ_watters

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    Staff: Mentor

    Not vapor, vapor pressure. We're talking about what is happening in the liquid and if/why it turns to gas. Saturation pressure and vapor pressure are equal here.
     
  13. Dec 1, 2014 #12
    What about super-heated water? I heard if you microwave deionized water in a clean cup you can get this.
     
  14. Dec 1, 2014 #13
    Heat and cool several times in a smooth container which does not promote bubbling to increase probability.

    But the only way is to decrease temperature of the liquid, at a high enough temperature every liquid turns to gas... the atmospheric pressure keeping bubbles in is comparatively minor in respect to that.
     
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