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I recently read an answer by Aman Rusia for this question: Is a liquid in a container always in equilibrium with its vapour?

In it, they say that

You can't have a container filled with only liquid. Think about that for a moment. Similarly you can't have a container filled with only ice. Some water, or water vapour, or even combination of the two will appear alongside.

However, my textbook says that

Imagine that you have a sample of water in a cylinder fitted with a piston at low pressure. Suppose that the temperature is held constant at 50 °C, and that weights are placed on a piston to exert a pressure of 1.0 atm. Only liquid water is present. The piston presses on the surface of the liquid. Now gradually reduce the pressure by removing some of the weights. At first, nothing seems to happen. The high pressure is keeping all the water molecules in the liquid state, and the volume of a liquid changes very little with pressure. However, when so many weights have been removed that the pressure has fallen to 0.12 atm (the vapor pressure of water at 50 °C), vapor begins to appear. The sample is now at the vapor-liquid boundary on the phase diagram. The pressure remains constant so long as the liquid and vapor phases are both present at equilibrium and the temperature remains constant. You are free to pull up the piston by an arbitrary extent, but enough water will evaporate to maintain the pressure at 0.12 atm. When you pull the piston out far enough, the liquid phase disappears; you are now free to modify the pressure of the vapor at will.

Atkins, Jones, and Laverman, Chemical Principles

So, is it true that you can have a container filled with only liquid?

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    $\begingroup$ Of course you can. Dive to the bottom of a lake (short of a lake, a bucket will do), and open your container there. Will some water magically boil and turn into vapor inside it? I don't think so. Maybe it will when you close the lid? Still unlikely. $\endgroup$
    – Ivan Neretin
    Commented Jul 9, 2019 at 15:44
  • $\begingroup$ Considering my textbook's information, what if gaseous nitrogen with a partial pressure of 1 atm was introduced to the piston? At what total pressure would the water vapor start to form, and at what total pressure would the liquid water completely vaporize? $\endgroup$
    – Cyclopropane
    Commented Jul 9, 2019 at 16:15
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    $\begingroup$ You can't have just liquid if its volume is smaller than that of the container. Is the wird "filled" that makes the difference, and in this sense the answer you mention is not accurate. The P of the liquid must balance vapour pressure. See @Karl answer $\endgroup$
    – Alchimista
    Commented Jul 11, 2019 at 9:19
  • $\begingroup$ Note that even your question can be interpreted. I would perhaps say "no" to the title question but answer "yes" to the last sentence. $\endgroup$
    – Alchimista
    Commented Jul 11, 2019 at 9:26

1 Answer 1

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In a tight, solid vessel, you can of course have a liquid (or any condensed phase) completely fill it.

There are basically three possibilities

  • the inside is at (potentially very) high pressure. no problem, water is compressible, just not very much, and also the vessel has a finite $E$ modulus
  • the inside is just at the vapour pressure of its content, but (because of the different expansion coefficients of vessel and content) the temperature must be kept perfectly constant at exactly the level where this is the case
  • the inside is below vapour pressure, but no gas bubble has evolved yet, that's principally an unstable condition, but if the deviation isn't large, it can stay practically forever.

Because of surface tension, there is even a small pressure range where the last case is actually stable.

I say your statement is basically right: You can have a completely filled vessel, but you can't do anything useful in it before it either bursts or bubbles.

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    $\begingroup$ For case 1, imagine a balloon filled with a liquid such as gallium (negligible vapor pressure at STP). Or a bellows, for that matter. $\endgroup$
    – DrMoishe Pippik
    Commented Jul 9, 2019 at 22:24
  • $\begingroup$ @DrMoishePippik So? The vessel excerts a certain pressure on the liquid, which tries to push back with its vapour pressure. If one of them wins, you are at points one or three, if they are identical, point two. $\endgroup$
    – Karl
    Commented Jul 9, 2019 at 22:35
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    $\begingroup$ Just citing an example... $\endgroup$
    – DrMoishe Pippik
    Commented Jul 9, 2019 at 23:09

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