Why does warm water freeze faster than cold water?

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   Astra Nomikposted 12 years ago

   Why does warm water freeze faster than cold water?

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   JThomp42posted 12 years ago

   The hot water is more likely to be supercooled. This means that the hot water's temperature is more likely to cool to temperatures below zero degrees Celsius. In the cold non-supercooled water, ice crystals form and float to the top, forming a sheet of ice over the top of the water, creating an insulating layer between the cooler air and the water. This ice sheet also stops evaporation. In the hot water that has become supercooled (thus, no longer hot) the water, when it does freeze, freezes throughout, creating more or less of a slush before freezing solid.
   
   Why is hot water more likely to be supercooled? Because hot water is less likely to contain tiny gas bubbles. Gas bubbles form from dissolved gasses as the water cools. When the hot water was heated, these dissolved gasses may have been driven out. In cold water, ice crystals use the tiny bubbles as starting points for formation (in physics, we call them nucleation points). But in the hot water, there are no bubbles, so there aren't as many starting points for the ice crystals.
   
   Dissolved gasses also lower the freezing point. Since heated gas is less likely to contain dissolved gasses, it's more likely to freeze first.

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      Astra Nomikposted 12 years agoin reply to this

      Wow, what a great explanation, JThomp42... 

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      JThomp42posted 12 years agoin reply to this

      Thank you!!

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   tussinposted 12 years ago

   it actually doesn't freeze faster than cold water and this is a common misperception that you can disprove experimentally at home.  Get equal sized containers and fill one with hot water and one with cold water. Place them both in the freezer away from each other and check on them periodically.  The container with cold water should solidify slightly earlier than the one with hot water. 
   
   I've done it and I can tell you that the container of hot water does not become ice sooner than the cold water.
   
   The reason why people say the hot water container will freeze faster is because initiially the *rate* of cooling is higher for the hot water container.  but once it cools sufficiently, it freezes at the usual rate.
   
   What JThomp42 said about the dissolved gasses is true.  But as the hot water cools, more gasses from air get dissolved in it, making it just like the cold water.

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      Astra Nomikposted 12 years agoin reply to this

      This sounds interesting.....

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   livingstaposted 12 years ago

   I am not very clear here, but you can check the 2 links below!
   
   http://library.thinkquest.org/C008537/c … reeze.html
   
   http://en.wikipedia.org/wiki/Mpemba_effect

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      Astra Nomikposted 12 years agoin reply to this

      Thank you for the links... they are awesome...

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   Teylinaposted 12 years ago

   I CANNOT ANSWER; however, I know six people (two of whom are "genius" level, and one Russian chemistry Ph.D. who sound just like JThomp, so I go w/him Glad livingsta remembers something! I have heard some of Tussin's points, but I also heard and saw them dispelled.
   ME??  I could care less.  All I know about freezing water is it can kill you or save your life, but if it is already frozen, all you gotta do is bust it up, stick in a warm can of beer, and in 5 min, 3 sec. it's the perfect cold to drink!  A ten people, 10 answer question

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   daskittlez69posted 12 years ago

   Basically when the water was heated it dissolved all over the tiny gas bubbles that were in the water. Because of this, ice crystals can not form and float to the top like in cold water.  So instead of freezing from the top down the water would freeze everywhere.

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