Eli5: Why does water expand while freezing, and what would happen if it was frozen in pressurized enviroment/container that cannot expand?
In: Physics
The water forms a crystal structure when it freezes. There is more room between the water molecules in the crystal structure. If the environment is pressurized enough, you can prevent it from freezing, you would need a very strong container though, because water freezing can crack through concrete and steel like it wasn’t even there.
There are a bunch of different types of ice, based on the temperature and pressure attained.
[https://en.wikipedia.org/wiki/Phases_of_ice#/media/File:Phase_diagram_of_water.svg](https://en.wikipedia.org/wiki/Phases_of_ice#/media/File:Phase_diagram_of_water.svg)
Edit: typo
When freezing the molecules arrange themselves in a fixed pattern, That pattern is more spread out than liquid water, thus expanding the volume. When cooling water below zero in a container part of the water would freeze increasing the pressure in the container and preventing more water to freeze. The cooler the water the more of it freezes. You can look at the phase diagram to see how much pressure is needed to keep water liquid under certain temperatures.
It expands because of how the water molecules are shaped and bond together. While liquid they can get very close, to form an ice crystal they have to take a specific orientation to each other. That orientation has pretty large gaps.
If you compress it one of two things happens: it remains liquid or it breaks the container. It takes a lot of pressure to keep it liquid, but it can be done.
This is why engine coolant has antifreeze in it. The pressure exerted by water when freezing is extreme. It will break open the steel of an engine block if it freezes.
Fill a steel pipe with water and cap it and submerge it in liquid nitrogen, [you get a boom](https://www.youtube.com/watch?v=t5mdZD00POs#t=4m15s).
> what would happen if it was frozen in pressurized enviroment/container that cannot expand?
There’s no such thing as a container that doesn’t expand as the internal pressure increases. The only way to achieve zero volume increase would be to actively increase the external pressure to compensate.
As the ice froze, the pressure would increase and this would compress the ice, keeping it smaller than it would be at normal pressures. The common water ice we see is hexagonal but there are many other water ice “phases”. Some of those that form at high pressures are denser than liquid water.
Molecules have a fairly rigid shape to them, in the case of water they’re shaped a bit like a flattened V. The ends of the V are attracted to the bottom of other Vs, (this is called hydrogen bonding – a bit beyond ELI5), but in a liquid they are moving with enough energy that they don’t stick. When water freezes, it’s because the molecules no longer have enough energy to overcome this attraction, and the tips of the Vs start to stick to other molecules. This causes the molecules to form a sort of structure – what we call a *crystal lattice*. This structure has more space in between the molecules because they form gaps to all line up well.
Moving passed ELI5, theres actually several forms of ice, go to [this](https://en.m.wikipedia.org/wiki/Phases_of_ice) page and scroll down to the section on crystal structure for some great renderings
Interesting to note that if ice didn’t expand and therefore float on water, our oceans would all be frozen as ice would sink to the bottom and not melt much
This is why pipes burst. The pressure the pipe puts on the water prevents it from freezing. When the pressure exceeds what the pipe can hold the water freezes all at once and pop goes the pipe.
Water expands when it freezes because the molecules arrange themselves in a way that takes up more space. If water is frozen in a pressurized container that cannot expand, the pressure will continue to increase until the container eventually breaks.
Water molecules have a peculiar property, in that they’re banana/boomerang shaped, with a permanent positive and negative electric charges at the ends (hydrogensl and the middle (oxygen) respectively. They’re a dipole.
When water freezes in normal conditions, this results in the crystal taking on a sort of sponge structure, with big voids between a lattice of water molecules. These voids are why the solid crystal occupies more volume.
As for what what happens if it’s contained, it depends on the strength of the container. Most will burst at their weakest point. But if they’re strong enough, they can force the water to stay liquid below a temperature where it would normally freeze, or take on a solid crystal structure that occupies less volume than the usual one.
Turns out ice can take on like twenty different arrangements at different temperatures snd pressures, with different properties.
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