Le 2011/09/05 18:50, Patrick Elliott a écrit :
> On 9/5/2011 10:47 AM, Darren New wrote:
>> On 9/5/2011 8:52, Invisible wrote:
>>> Yes, but under /normal/ circumstances, it boils at 100°C, which is why
>>> it's
>>> defined that way. :-P
>>
>> No it doesn't. At 100°C, it's in equilibrium. Just like at 0°C, it's
>> neither getting more frozen or less frozen.
>>
> Worse than that, in certain conditions you can "hyper-heat" water, and,
> I assume, probably super cool it, without changing state. In the former
> case you just need a container that has "no" places for bubbles to form.
> Not sure what you would need to do in the later case to make it happen,
> if you could.

You can have water that stay liquid down to -10°C and possibly even 
less. You need a container with very smooth surface and no particles in 
suspention. In this state, a vibration can be just enough to cause 
almost instant crystalisation.

If you slowly heat very pure water, it can bet a good bit warmer that 
100°C before it start to boil. There will be vapour escaping from the 
surface, but no ebulition, even in a open container. It's a dangerous 
situation, as any disturbance can cause explosive ebulition projecting 
scalding water everywhere.

If you slowly cool down steam and don't give it any nucleation point, 
that steam may stay totaly gaseous at relatively low temperature. You 
get hyper-saturated steam. It appens in, and around, clouds. Again, it's 
an unstable situation and even a very faint sound, or a dust particle 
can cause almost instant condensation.

But you can't prevent ice from melting as you slowly heat it.

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