question about the basic properties of water

[theben]

sometimes when i take a .5L bottle of water out of the freezer, it is in a liquid state but when i open the bottle, it then starts to partially freeze. it turns into a slushy, clouded mixture from its usual transparent, liquid state. it seems to develop some ice crystals. i have a feeling the act of opening the bottle may speed up or start this process, but i am not sure because i always open the bottle (no testing of other outcomes)

what is going on

[udontknowmickey]

change in pressure possibly?

At lower pressures substances tend more towards the fluid state (that's not a good description, but it's the best I could come up with)

[pzhon]

The water is probably supercooled (http://van.hep.uiuc.edu/van/qa/section/States_of_Matter_and_Energy/Melting_and_Freezing/20030802043219.htm). Phase transitions don't have to happen at the usual freezing and boiling points, and water can easily be in a somewhat unstable supercooled or superheated state if there is no impurity or singularity about which to start the transition.

I'm not sure what is going on as you open the bottle. I've noticed the slush formation in 16 oz. glass bottles of soda, too. It could be that changing the pressure makes it easier for ice to form at the surface, and then it propagates. However, there might be something else going on with the change of pressure.

[theben]

i also should add the water in the bottles is refilled, carbon filtered tap water

[chezlaw]

[ QUOTE ]
sometimes when i take a .5L bottle of water out of the freezer, it is in a liquid state but when i open the bottle, it then starts to partially freeze. it turns into a slushy, clouded mixture from its usual transparent, liquid state. it seems to develop some ice crystals. i have a feeling the act of opening the bottle may speed up or start this process, but i am not sure because i always open the bottle (no testing of other outcomes)

what is going on

[/ QUOTE ]

Just a guess but some of the water turns to gas when the bottle is opened (gas being held in liquid form due to the pressure?). The gas is at the same temp' as the water and some energy is needed for latent heat. This cools the water, ice forms.

chez

[Girchuck]

When you have slightly supercooled water you need crystallization nodes for the ice to form. When you open the bottle, dust in the air outside comes in contact with the water inside and serves as just such nodes.