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.

Jim

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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

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Le 2011/09/05 11:52, Invisible a écrit :
> 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

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.
(0°F is defined as the freezing poing of sea water and 100°F as the body 
temperature of a "healthy" human male, but the "healthy" human male who 
was used for the original mesure was somewhat feverish at the time, and 
had the flue the next day...)

Change the presure and you also change freezing temperature.


Alain

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Alain <aze### [at] qwertyorg> wrote:




  So, does water freeze or melt at exactly 0 degrees celsius?

-- 
                                                          - Warp

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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] qwertyorg> 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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