What happens to P when a vessel of water with no headspace is heated?

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Discussion Overview

The discussion revolves around the behavior of pressure in a completely filled vessel of water when heated, specifically addressing the implications of having no headspace. Participants explore the applicability of vapor pressure equations, the compressibility of liquid water, and the effects of reaching supercritical conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the equations for vapor pressure apply in the absence of vapor space when heating a fully filled vessel.
  • Another participant expresses uncertainty about the specific equations governing pressure changes and whether these change with varying amounts of headspace.
  • A participant raises the question of liquid water's compressibility and the validity of vapor pressure equations without vapor present.
  • One contributor speculates that pressure will increase significantly due to water's expansion when heated, suggesting that under supercritical conditions, the distinction between liquid and gas may disappear.
  • Another participant proposes that as temperature increases, the liquid water may transition into a supercritical fluid without a sudden phase change.
  • A later reply suggests performing calculations to verify the consistency of water remaining in a liquid or supercritical state under constant density conditions.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of vapor pressure equations and the behavior of water under heating without headspace. There is no consensus on the specific equations or models that should be used to describe the pressure changes.

Contextual Notes

Participants note the complexities involved in the behavior of water under extreme conditions, including the potential for exotic ice forms and the transition to supercritical fluids, but do not resolve these complexities.

Who May Find This Useful

This discussion may be of interest to those studying thermodynamics, fluid mechanics, or phase transitions in materials, particularly in the context of water's unique properties.

benwade90
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Assume we have a vessel capable of withstanding infinite pressure. What happens to the pressure inside the vessel when that vessel is filled completely with water, with no air space at the top, and is then heated? Do the equations for vapor pressure still apply if there's no space for a vapor?

Also, what happens when you reach supercritical temperature/pressure combinations?
 
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What do you think will happen?
 


Well I don't know precisely, which is why I'm asking for help. Obviously pressure will increase, but what I don't know is if it's predicted by a whole different equation than the equation for vapor pressure. Does it change as a function of the amount headspace (0% headspace vs. 15% vs 58%, for example)? Does it change to a whole new regime under supercritical conditions? Stuff like that.
 


Is liquid water compressible or incompressible? If there is no vapor, will the vapor pressure equation be valid?
 


I reckon not. That's what I was trying to ask with "Do the equations for vapor pressure still apply if there's no space for a vapor?" So that being said, how do you describe pressure in a heated liquid that has no room for expansion?
 


I don't know, but I can guess. Water expands quite a bit when heated, so, given an invincible container, the pressure must get very large very fast. So no gas will form. Now either, you keep increasing the temperature beyond the critical temperature of water, and the distinction between liquid and gas disappears, or, perhaps even weirder you will get some exotic forms of ice like ice VII, X, or XI, according to the phase diagram here.
http://www.lsbu.ac.uk/water/phase.html
(Water is crazy!)

I don't think you will actually get these ice forms, because those exotic ice forms are denser than water, so the pressure would not increase beyond a certain point. Rather, you would probably move in a curved path that takes you from liquid water over the critical point, and you will have a supercritical fluid. Note that there is no sudden change from a liquid to a supercritical fluid. As you increase the temperature, the liquid just gradually transforms into a supercritical fluid.
 
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I think Khashishi is correct. But, why don't you do a calculation just to see? If the container does not expand, then the average density of the water in the container is constant while you heat it. See if this is consistent with the water remaining all liquid (or supercritical liquid). Almost certainly it is.
 

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