What happens to water in an unbreakable pressure cooker?

I posed this question to my high school chemistry teacher who didn’t have an answer. It came up when he was explaining about how the boiling point is higher at higher atmospheric pressure. So then I asked him, what if you have a hypothetical unbreakable pressure cooker with no escape valves, and you fill it completely with water so there is no air at all? He didn’t know. Does it stay liquid forever? Turn to steam? Plasma? I’ve heard that the gas giant planets may have a core of metallic hydrogen due to the extreme pressures, would you get metallic water?

If the unbreakable container was filled 100% with water and not even a minute amount of air space, it couldn’t turn to steam because there would be no room.

Since liquid water is the most compact form (water is one of the rare things that actually gets bigger when it turns solid) it would probably stay liquid, but with absolutely no boiling point. You could get that sucker to 2 thousand degrees, and it’d still be water.

This is probably more than you wanted to know, but somewhere around figure 5.12 is the phase-diagram of water:



Lifting the lid to have a look-see is not advised, however.

'bout water n its solid form being larger then its liquid form.
What if you flash-froze water very very quickly? Somehow removed the heat from it so fast that it didn’t get a chance to align into its crystaline form?
Wouldn’t it become a solid, a glass, with a greater density then the liquid?

I specifically remember studying this type of situation in my college physics courses. Mikahw has it right. When water phase-changes to steam, it is because the water molecules are excited enough by the heat they’ve absorbed to break their normal bonds (such as surface tension) and spread out into the gas we know as water vapor. If this happens within a confined space, it generates quite a lot of pressure, which is the principle a steam engine runs on. But in the situation described, it is impossible for the phase change to take place. The water cannot change into a form with more volume, because there is no more space for it. So it would essentially become super-heated, while building up an incredible amount of pressure inside this hypothetical cooker. If the volume was increased at all, a certain amount of the water would instantly turn to steam.

Kyberneticist, I think that you’d get liquid water that was below the normal freezing tempature of water. It would begin to turn to Ice after a short time. I think anyways. Not like I have a Master’s degree in water phase changes, heh.

Conversely, if you put a can of beer in the freezer, it will turn into subzero liquid beer. If you then open it, it will instantly freeze.

My wag
at temp increased the vapor pressure might compress the liquid enough to allow some steam. (water IS compressable - but not much - and that no wag) as temp further increased the water ‘might’ hit a state where the whole thing became gas/plasma in a very short time (less then 1 second). After the plasma, the bonds might break between H and O. further the H’s might get together to form He or heavy H in some fusion reaction. further still and the nucleuses might become fly apart to form a diffren ttype of plasma that I can’t remember now - i think that’s about it. If it was compressed you might be able to combine electrons and protons into neutrons (i.e. neutron star). Maybe the quarks would seperate out.

Imagine what that pressure cooker would do to chicken!

Mmmm…chicken singularity…

The key to this part of your question is the fact that hydrogen is a metal. It is the only metal that is gaseous at STP. Becoming metallic is not something that happens when a substance is compressed, but it is an innate property of the element itself. Water is not a metal since it is a compound of hydrogen and oxygen and compounds, by definition, cannot be metals. One of the most basic properties of all metals is the conduction of electricity. Pure water is not a conductor.

Actually, if you keep adding heat to the water, it reaches a critical point at something like 373 degrees centigrade. At this point, neither the liquid nor the gas phase is favoured, and you would get something like boiling and raining at the same time in the cooker. Above this temperature, you would have a container of supercritical fluid. This is very useful stuff for making decaffeinated coffee etc.

Secondly, liquid is not the most “compact” phase of water. The phase transition from liquid to Ice II (that’s ice two) involves a decrease in volume, for example.

Aww, Hibernicus, I was gonna say that! (Guess what my chem class coverd today). But yeah, eventually it would get to the critical point, and the gas and liquid parts would be the same density, and there wouldn’t be a line between them. It looks really nifty. :slight_smile: