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Old 26 September 2008, 04:39 PM
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Glasses Freezing/boiling: hot water vs. cold

Comment: PLEASE put to rest the widely held belief that cold water boils
faster than hot water!

The myth may have arisen from the fact that cold water does absorb heat
faster than hot water. However, once the water gets to a hotter (not yet
boiling) temperature, it absorbs heat at a slower rate, and from that
point it takes just as long to bring the water to a boil as it would if
the water were hot to begin with. And because it takes cold water some
time to reach the temperature of hot water, cold water actually TAKES MUCH
LONGER TO BOIL THAN HOT WATER DOES.
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Old 26 September 2008, 04:39 PM
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Glasses

Comment: I remember hearing years ago that hot water freezes faster than
cold water because hot water has less oxygen in it. This seems
counter-intuitive. Today I heard the same thing told to me as fact.
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  #3  
Old 26 September 2008, 04:51 PM
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geminilee geminilee is offline
 
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Quote:
Originally Posted by snopes View Post
Comment: I remember hearing years ago that hot water freezes faster than
cold water because hot water has less oxygen in it. This seems
counter-intuitive. Today I heard the same thing told to me as fact.
It is true, sort of. Boiling water does freeze faster, because of evaporation cooling it very quickly, and also because as it evaporates there is less volume to freeze. So you end up with ice quicker, but there is less of it.

I have no idea where anyone got the idea that cold water boils quicker, though. That one my (admittedly limited) knowledge of chemistry says is bunk.
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  #4  
Old 26 September 2008, 05:34 PM
bcampbell
 
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Quote:
Originally Posted by snopes View Post
Comment: I remember hearing years ago that hot water freezes faster than
cold water because hot water has less oxygen in it. This seems
counter-intuitive. Today I heard the same thing told to me as fact.
This is the Mpemba Effect and it deals with warm water vs cold water, not hot or boiling. As the article states, there are many possible explanations for the effect.
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Old 29 September 2008, 04:50 PM
Kahdra Kahdra is offline
 
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Quote:
Originally Posted by geminilee View Post
I have no idea where anyone got the idea that cold water boils quicker, though. That one my (admittedly limited) knowledge of chemistry says is bunk.
Someone explained it to me using "boiling point elevation" (the colligative property). Basically, the warm tap water has more stuff from the pipes dissolved in it, so it boils at a higher temperature than cold tap water. I don't believe this. I mean, I believe in colligative properties, but I do not believe that warm tap water can dissolve enough stuff to measurably effect its boiling temperature.
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  #6  
Old 01 October 2008, 06:28 AM
Troberg Troberg is offline
 
 
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Quote:
This is the Mpemba Effect
That's such a cool story! Mpemba definately has the mind of a scientist!
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  #7  
Old 01 October 2008, 06:49 AM
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llewtrah llewtrah is offline
 
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Quote:
Originally Posted by geminilee View Post
I have no idea where anyone got the idea that cold water boils quicker, though. That one my (admittedly limited) knowledge of chemistry says is bunk.
When I was still primary school age, my mother used to tell us to put cold water in the kettle as "it boils hotter". By the time I learnt enough chemistry (impurities, boiling/freezing points of elements, mixtures and compounds) and physics (pressure/temperature/volume relationships) to dispute this statement, she'd forgotten ever making it
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