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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.
--
Darren New, San Diego CA, USA (PST)
How come I never get only one kudo?
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On Mon, 05 Sep 2011 16:52:50 +0100, Invisible wrote:
> On 05/09/2011 04:43 PM, Jim Henderson wrote:
>> On Mon, 05 Sep 2011 10:35:45 +0100, Invisible wrote:
>>
>>> that water freezes at 0°C (actually no, it
>>> doesn't) and boils at 100°C
>>
>> It also doesn't always boil at 100C - reduce the atmospheric pressure
>> and see when it boils.
>
> Or increase it. Or add impurities. Or whatever.
>
> Yes, but under /normal/ circumstances, it boils at 100°C, which is why
> it's defined that way. :-P
Not here at 4,000 feet - "normal" circumstances here have it boiling at a
slightly lower temperature. :P
IOW, it all depends on how you define "normal". (Hence my suggestion of
reducing the atmospheric pressure, because here, lower pressure is
'normal').
Jim
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On Mon, 05 Sep 2011 13:17:32 -0400, Warp wrote:
> Alain <aze### [at] qwerty org> wrote:
>> Pure water at average sea level presure boils/condense at 100°C and
>> melt/freeze at 0°C at the same presure level. Both by definition. In
>> fact, it's the definition of 0°C and 100°C.
>
> So, does water freeze or melt at exactly 0 degrees celsius?
Yes, at some altitudes, it does.
Jim
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>> Yes, but under /normal/ circumstances, it boils at 100°C, which is why
>> it's defined that way. :-P
>
> Not here at 4,000 feet - "normal" circumstances here have it boiling at a
> slightly lower temperature. :P
96.2°C, a piffling 3.8° lower.
> IOW, it all depends on how you define "normal". (Hence my suggestion of
> reducing the atmospheric pressure, because here, lower pressure is
> 'normal').
This is why the /actual/ specification is far more complicated. But for
any sane real-world purpose, you can more or less ignore such
technicallities.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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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.
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> Alain<aze### [at] qwertyorg> wrote:
>
> So, does water freeze or melt at exactly 0 degrees celsius?
>
At sea level, yes. Melt if you add energy, freeze if it looses energy,
As you climb or reduce presure, the freezing point slowly climb, but not
much.
As you go lower or increase presure, the freezing point goes into the
negative.
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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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On Mon, 05 Sep 2011 21:12:15 -0400, Alain wrote:
> 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.
Which is actually quite cool to see - I've seen it done with beer before.
Jim
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On Mon, 05 Sep 2011 19:32:49 +0100, Orchid XP v8 wrote:
>>> Yes, but under /normal/ circumstances, it boils at 100°C, which is why
>>> it's defined that way. :-P
>>
>> Not here at 4,000 feet - "normal" circumstances here have it boiling at
>> a slightly lower temperature. :P
>
> 96.2°C, a piffling 3.8° lower.
Which is still not 100C no matter how you slice it. The difference in
humidity, altitude, and other things makes cooking things that require
precise measurements (usually baked goods) slightly different than at
other altitudes and in other conditions.
>> IOW, it all depends on how you define "normal". (Hence my suggestion
>> of reducing the atmospheric pressure, because here, lower pressure is
>> 'normal').
>
> This is why the /actual/ specification is far more complicated. But for
> any sane real-world purpose, you can more or less ignore such
> technicallities.
Baking is a real-world purpose. An awareness of the 'normal' as well as
'current' environment are, for some things, absolutely *critical* in
order to be successful.
Jim
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On 06/09/2011 06:25 AM, Jim Henderson wrote:
> On Mon, 05 Sep 2011 21:12:15 -0400, Alain wrote:
>
>> 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.
>
> Which is actually quite cool
I see what you did there.
I've got a box of hand warmers at home. They contain a super-saturated
solution (of what I don't know). Once you provide a nucleation point,
the whole lot crystallises within a few seconds. It also gets quite warm
in the process. (This is what makes it good for warming your hands.)
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