Why Does Water Freeze?

Most recent answer: 05/06/2015

Q:
Why water get solid when we cool it?
- Krishna Kant (age 15)
Patna,Bihar,India
A:

We discuss the answer here:

https://van.physics.illinois.edu/qa/listing.php?id=1730

Here's a simpler version.

Things tend to arrange themselves in whatever way makes the most possible microscopic (quantum) states. (We say that "entropy is maximized.") Liquid water has more states than ice, because the molecules can tumble around different ways in the liquid instead of lining up in the ice pattern. So why does the liquid freeze when it's cold?

When the molecules line up to make ice, they arrange in a pattern that has lower energy than the jumbled liquid. The energy released help other things around reach more quantum states. How many more? That depends on temperature. Below 0°C, enough more to more than make up for the loss of states when the molecules line up. Above 0°C, not enough to make up for that loss.

Mike W.


(published on 05/06/2015)