Question about ice

[Joolee1980]

I put a new unopened room temperature 500ml bottle of mineral water in the freezer to cool it down quickly and forgot about it for nearly 3 hours. When I went to take it out I was surprised to see it was still clear and unfrozen looking, but as I held the bottle the water turned to opaque ice starting from the top and reaching the bottom in about 3 or 4 seconds. How did that happen?

[MarkRae]

Pressure.

[DTCwordfan]

Look up Boyle's and Charles' laws if you want the physics......

[Joolee1980]

What do you mean "pressure"?

[Hymie]

How has the pressure within the bottle changed – just as it was taken out of the freezer?

[heathfield]

Watch and learn...

http://www.bbc.co.uk/...dson/super_cool.shtml

[Joolee1980]

Heathfield - thanks for that useful link, that makes complete sense to me now. Nucleation then, not "pressure".

[beso]

An interesting product that uses a supercooled liquid with a nucleation source are those little heat packs.

The crystals in the pack are melted by immersing the pack in hot water. Then it is allowed to cool to room temperature. It remains a liquid because there is no nucleation source.

They are activated by pressing a small button inside. This exposes a nucleation source and the immedialtely crystallise giving out a considerable amout of latent heat of fusion.

Another example involving boiling is putting a very clean Pyrex container full of water in a microwave. The water superheats but will not boil because there is no nucleation source.

Removed from the microwave the disturbance can cause nucleation and the whole container of water boils violently. It is a very common source of scalding injuries.