Eli5: Why does water expand while freezing, and what would happen if it was frozen in pressurized enviroment/container that cannot expand?

Question

Eli5: Why does water expand while freezing, and what would happen if it was frozen in pressurized enviroment/container that cannot expand?

In: Physics

Answer 1

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