Eli5: How does water expand in a closed container? Shouldn’t it shrink and be compact as it forms into a solid which has tighter molecules?


Context: I was trying to figure out why my coke glass bottle exploded in my freezer.

Update: As it turns out, water is a weird one amongst other liquids.

In: 3

Water is one of very few compounds that expands when it freezes. It expands because the solid crystalline structure has large voids, whereas the liquid form doesn’t.

Frozen water is a rare material that expands when it freezes. It’s why ice floats. The way the molecules stick together pushes them apart compared to the free floating liquid. Most solids don’t do this.

Water does, in fact, shrink as it cools. However, as it freezes the hydrogen atoms of each molecule want to bond with each other and that forces the molecules to push apart to form those bonds.

Think about it like this: you get a bunch of people and squeeze them closer and closer together. This is the water cooling. Now, in order to form a solid, everyone needs to hold hands. You can imagine that since the people are so close together they need to push apart a little to be able to actually hold hands. This is like the water starting to freeze. As more bonds are made (hand holding) they need to spread further out because their bodies are in the way.

Edit: as u/Saavedroo pointed out below, my analogy here implies the hydrogen bonds with each other instead of with the oxygen. I made a slight edit for more clarity but in hindsight I should have replaced “hold hands” with “place a hand on another’s shoulder.”

Plutonium is of the few other substances that behaves in the same way.
When plutonium melts it forms a denser liquid than the solid metal – and plutonium being plutonium this means things could get very exciting indeed as a subcritical block of plutonium metal could become critical simply by melting – shortly after which everything else begins melting.
In fact plutonium is just plain weird – it has six different crystal forms with wildly different densities. Heating and cooling the metal makes it change crystal form – and once again it can go from reasonably safe sub criticality to ruin-your-day criticality just by a temperature change. Nuclear weapons avoid this problem by alloying plutonium with a small amount of gallium, aluminium or indium which prevent it from changing crystal forms.

Answer: Water is magnetically charged, with positive and negative sides. You can bend falling water with an electric charge.

Warm water has a lot of energy, which is greater than the magnetic force. Cold water will attract itself while hot water won’t.

Even cold water has enough energy for the molecules to have enough energy to not stick magnetically. Once it does have that energy, the magnets take over and form a crystal much larger and stronger than the water before.

Water is like a magic puzzle, if you move the pieces all around they fit in a tiny box and flow, if you let the piece slow down, they will form the picture on their own as be much bigger than the pile of pieces.