Can Gas Pressure Exceed Out Pressure?

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Discussion Overview

The discussion revolves around the question of whether gas pressure can exceed outside pressure, particularly in the context of liquids and their boiling points. Participants explore concepts related to vapor pressure, boiling, and super-heated water, with a focus on the conditions under which these phenomena occur.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant wonders if gas pressure can exceed outside pressure and asks for clarification on how this might occur.
  • Another participant expresses confusion regarding the initial question and requests a more detailed description.
  • A later reply clarifies that when gas pressure of a liquid equals outside pressure, boiling occurs, and questions whether gas pressure can be greater than outside pressure.
  • Some participants discuss the concept of vapor pressure, noting that it cannot exceed ambient pressure without resulting in a phase change.
  • There is a mention of super-heated water and its behavior when heated in a microwave, suggesting that it can exist in a state where pressure conditions are altered.
  • Participants debate the distinction between vapor pressure and the pressure of the liquid, with some asserting that saturation pressure and vapor pressure are equal in certain contexts.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial question, with multiple competing views regarding the relationship between gas pressure, vapor pressure, and boiling. The discussion remains unresolved, with ongoing clarification and debate about the concepts involved.

Contextual Notes

There are limitations in the clarity of the initial question and the definitions used by participants, leading to confusion and differing interpretations of the concepts of gas pressure and vapor pressure.

jukzzhd
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i wonder if "gas pressure > out pressure" this can be possible. if so how?
 
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Ahem. What?
 
voko said:
Ahem. What?
Copy that...
 
sorry for bad translation. that was all i can do
 
I do not understand the question in #1. Rephrase it.
 
jukzzhd said:
sorry for bad translation. that was all i can do
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.
 
as we know when the gas pressure of a liquad is equal with the outside pressure, liquid starts to boil. I am asking that if the gas pressure of a liquid can be "bigger" than the outside pressure.
and yeah its both description and translation problem
 
jukzzhd said:
as we know when the gas pressure of a liquad is equal with the outside pressure, liquid starts to boil
No, that is not true. At every free air-water interface (every lake, river, sea) the pressures are exactly equal. Is there any boiling?
 
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).
 
  • #10
russ_watters said:
If it tries to be, the water just instantly flashes to steam

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?
 
  • #11
voko said:
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?
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.
 
  • #12
What about super-heated water? I heard if you microwave deionized water in a clean cup you can get this.
 
  • #13
Khashishi said:
What about super-heated water? I heard if you microwave deionized water in a clean cup you can get this.
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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