Cloudy ice cubes

[Jimmyjazz]

Recently I put a couple of ice cube trays into the freezer. After a couple of hours I opened the freezer and before my eyes the cubes suddenly turned cloudy, seemingly from the bottom up.

Obviously there was some kind of chemical reaction going on, can anyone tell me exactl what?

[remesses]

there are a few posibilities
but before i explain let me ask you why is snow white and ice see through?
well this kinda explains your question some parts of the cubes cools faster than others if it cools slowly it will form a transparent latice but if it cools to quickly it crystalises and apears opaque... hence your ice compries of both of these variations. obvioulsy your ice cooled unevenly and it was colder at the bottom of the tray than at the top.

[gen2]

If clean water is cooled in a clean container and left undisturbed, it does not freeze as soon as its temperature drops below 0 degrees C. Instead, it becomes 'a supercooled liquid'. The disturbace caused by opening the freezer triggered the freezing process.

[Space]

I agree with gen2,
you just witnessed supercooling

[brachiopod]

Yep, you witnessed the 'instant freezing' of a supercooled liquid.

This, of course, is a physical reaction, not a chemical reaction, as it only involves a change of state (ie liquid to solid) - not a change in chemical composition.

[Andy Peaty]

Just pop a few cubes in a glass of beer and chill out. Andy