Why does water expand upon freezing?

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My mother always asks me not to fill the ice cube tray with water to the brim because it’ll expand and break the box. But doesn’t matter shrink in volume when heat is dissipated, so why does the ice cube expand?

Sorry in advanced, if I word it incorrectly, English is not my first language. Thank you.

In: Physics

5 Answers

Anonymous 0 Comments

While heat tends to favor things expanding, it’s really about stability and (relatedly) free energy, really. While the general trend is that if you heat something up, it will expand, the state transition for water is different here.

Basically, water in solid form has a crystal structure. This structure is less dense than its liquid form. When all the molecules are free to move and slide around each other, they actually compact slightly better than if they were rigidly held in place.

Relevant image: https://chem.libretexts.org/@api/deki/files/78717/CK12_Screenshot_15-2-1.png?revision=1&size=bestfit&width=508&height=249

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