[another_someone]

Yes. It gives off heat because the particles become more closer together and lose energy. But still isnt the "thing" itself, cold? Not the thing which is given off.

There are two different issues - the heat caused by compression, and the heat brought about by the change in state (from gas to liquid, and from liquid to solid).

You are correct, that as heat is merely the action of atoms bouncing off one another, so the closer to push the atoms, the more opportunity they have to bounce of each other, and so you get more heat.  In terms of the heat of compression, this is the simple answer.

When you get to a change of state, it gets a little different, because you are the amount of freedom that the atoms have to move by the structures they form (in a gas, atoms have total freedom of movement, in a liquid they are constrained by certain forces but still have a fair degree of movement, while in a solid, the atoms are all locked into place).  In creating those structures heat is given off that is nothing to do with the heat of compression.

[Seany (OP)]

OK. So we could make heat energy by compressing water?

[another_someone]

You will certainly have the heat of compression as water is compressed.

The bit I am not sure about is the formation of ice.

As I said above, in most materials, the liquid is very loosely bound, and when the material becomes a solid, the form in which the atoms are locked into the crystal structures of the solid is more compact than the loose form of the liquid.  If one was talking about most other materials, and one discussed compressing the liquid, I would have no doubt that it would form a solid crystal, and as it does so, it will give off even more heat than would be accounted for merely by the compression of the liquid.

The problem is that water is in fact a very strange substance with unusual properties.

If you look at a water molecule, it is H₂O, while a molecular weight of 18, while the oxygen gas in our atmosphere is simply O₂ with a molecular weight of 32.  Looking simply at the weights of the molecules, water ought to be a gas at room temperature (steam is in fact lighter than oxygen at the same temperature).

Because of the peculiar way the hydrogen and oxygen create an electric field around the water molecule, it causes water molecules to be strongly attracted to other water molecules in a way that oxygen molecules are not attracted to other oxygen molecules.  So, this attraction between water molecules allows water to become a liquid (at normal atmospheric pressure) at temperatures at 376 kelvin (100 centigrade), while oxygen will not become liquid until you get down to 90 kelvin (-186 centigrade).

The attraction between water molecules is so strong, that below around 4 degrees centigrade (280 kelvin) it can actually keep the water molecules more tightly packed in a liquid form than they would be allowed to be in the solid lattice structure of ice.  For this reason, while in most matterials, if the solidify, the solid lumps will fall to the bottom of the liquid; whereas with water, the solid form (i.e. ice - such as icebergs) will float on the water.  It is also the reason why, if water within pipes is allowed to freeze, the expanding ice can cause the pipe to burst.

It is for this reason that I am not sure if you compress water it will form ice.  Since the ice is going to try and expand, and you are applying high pressure to the water, it will have nowhere to expand to, so I am not sure how it will react.

[Seany (OP)]

Yes.. That was most interesting. Let's just try Neil's method of squeezing it with our fingers. []

[Ben6789]

This question can have quite a few answers, depending on variables.

Firstly, while most liquids can shrink by becoming sold, water is one of the exceptions in that crystalline ice takes more space than water at the same temperature.  It is possible you may form amorphous ice.

If you squeeze hard enough (harder than would be possible with anything on Earth), the electrons would fuse into the nucleus of the atoms, creating neutons (this is what happens in a neutron star - but under immense gravitational force).

Increase the pressure even harder, and you will form your own black hole (although a very small black hole would be unstable).

Making black holes just by adding lots of pressure? If it did..what would happen to the thing compressing it? Would that get warped? Destroyed? Would anything happen to it at all?

[Seany (OP)]

Ahh.. That is so interesting Ben.. But personally, I don't think a black hole can be made by adding lots of pressure.

I thought that blackholes were made, when stars run out of gases to burn and eventually shrinks so small, but with a mass so big, turning into a black hole. Well, that's what I thought.

[DrDick]

I have tried to make a crude phase diagram for water using the diagram creation ability of the board.  I haven't tried this before - let's see how it works.   []

Compression of water has different effects depending on the conditions at the time.  Compression does release heat, but if you do it slowly enough, the heat is lost during the compression.

Looking at the phase diagram, there is a region where if you increase the pressure at constant temperature, solid water (ice) will change into liquid water (melting).  For quite some time, it was thought that this was how skating worked, by melting a thin layer of ice below the skates.  Now it is realized that any melting from this effect would be too slow to have any effect, and there are other (more complex) reasons given.

If you keep increasing the pressure, however, the liquid will eventually solidify again - not from getting colder, but from increased pressure.  Of course, this would be a different kind of ice than what we're used to.  There are several different phases of solid water, with phase boundaries between them just as there are phase boundaries between solid and liquid phases, or liquid and gas phases, etc.

Eventually, with enough pressure, the molecules of water would get close enough that the hydrogen atoms would start combining and you would get nuclear fusion.

Keep going, and you would eventually get the black hole mentioned earlier.

Dick

[Seany (OP)]

Oh. Thanks DrDick. It makes sense now. Quite scary, the whole thing []

[DrDick]

Oops, I forgot to insert the drawing into the message. [:I] Let's try again.   (Should've previewed the message first, I guess.)


[diagram=185_0]

[Seany (OP)]

Lol I was wondering what you were going on about the diagram lol []

[paul.fr]

the first thing that happens when pressure is applied to a molecular system such as water is that the distance between the molecules is reduced and if there are any rotations or phase changes etc. that can happen to reduce the stress [LeChatelier’s principle] they will happen. This is what happens in the water-normal ice [Ice Ih or hexagonal ice]. This ice is less dense that water so if a pressure is applied to a system of this ice and water the ice simply melts [or possibly vaporizes if the pressure is from an inert gas] to reduce the pressure and the freezing point lowers.

http://www.madsci.org/posts/archives/mar97/859148048.Ph.r.html ice is described here" http://skua.caltech.edu/hermann/ice.htm

The next link describes it all with a good phase diagram. http://www.ill.fr/AR-97/page/05chemi.htm

It is rather difficult to compress the space between atoms in a simple molecule because there is no space; there are electrons in their lowest orbitals. These orbitals usually occupy the smallest possible volume and while they are compressible the energy required is fantastically high and there are no readily available relaxation processes that allow a lower volume. One possible mechanism is positive ion formation with ejection of an electron [piezoelectric effect] since positive ions are usually much smaller than the neutral atom or molecule. Topics to look up here are Vibrational and electronic spectra of molecules and the Franck-Condon Principle. These show that pressure, while raising the energy of a molecule, doesn’t usually permit excitation of that molecule to higher energy states because the higher states are of greater volume. So what can happen?

Molecules can rearrange to forms that are of less volume; the classic example is the graphite to diamond transformation. Crystal forms can rearrange to more compact forms. Finally in water there are weak bonds, hydrogen bonds, that have longer than normal bond lengths. These are compressible. All these things happen in ice at extremely high pressures. It also happens that some of these ice forms are stable at temperatures above zero C to really quite high temp possibly even to the critical point. The second and third links describe the processes well. The third link has a good phase diagram describing the many phases of ice and several models of some of the structures.  however, the compression still is not really taking place in the atom but in the longer bonds between molecules. However, at least one form might contain hydronium[H3O+]] ions which means that the space between the H and O atoms was compressed to force a rearrangement.

[Seany (OP)]

Sorry Paul! I know you're trying to help, but as a 13 year-old.. I really can't understand. I've read it through twice []

[Batroost]

Or if you want to see it from a slightly different point of view... Ice comes in different kinds which depend on both pressure and temperature.

Try typing Ice I, Ice II, Ice III, Ice IV, Ice V, Ice VI etc... into Google.

Ice I is the 'normal' Ice you find in a fridge. The others form under different pressures and temperatures.

Ice VI looks particularly interesting:- forms from Water at ~273 K (that's its normal 'freezing point') and 1.1 GPa pressure (that's about 10,000 atmospheres)! Appears to be stable at higher temperatures (>80 degrees C) if you increase the pressure and has a higher density than water.

So... depending on how you vary the temperature and pressure there are a range of different Ices you could end-up with.

[Ben6789]

But what about the black hole? After it's created what will happen to the equipment compressing it? Warped? Destroyed? Sucked to another dimension?

[Seany (OP)]

Ben, I guess we will never find out []