Expanding Cold Water

Most recent answer: 10/22/2007

Q:
When anything is cooled the molecules shake less violently. They contract, right? And when the sea is warmed it expands, right? So why is it that when you put a bottle of water in the freezer, there is less room in the bottle? As though the water has expanded?
- Seb (age 16)
Sydney, Australia
A:
It does expand when it freezes. It happens that water molecules can settle into a low-energy (cold) solid state in a particular arrangement that’s expanded a little compared to the liquid jumble. That’s unusual for liquids, but happens for a few. There’s no law of nature that says that the low-energy states are always more compact.
There’s a trace of this behavior even noticeable in the liquid state, which quits contracting and starts to expand when cooled below 4°C.

Mike W.

(published on 10/22/2007)