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Thread: diffrence in temperature

  1. #1 diffrence in temperature 
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    Earlier today i was told that if you put to samples of water into a freezer, one was boiling and one was at room temperature, the boiling one would freeze faster.
    can somebody explain to this to me please....


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  3. #2  
    Forum Isotope Bunbury's Avatar
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    I'd suggest it is possibly true under some conditions, but by no means always true. The hot water will lose mass by evaporation so the mass of water that has to be frozen will be smaller than the mass of room temperature water. The key would be the geometry of the container. A flat wide dish with a large surface area would lose a lot of water by evaporation. This might mean that the remaining smaller mass of water would freeze faster than the larger mass of water that started at room temperature. A container with a small opening would lose less by evaporation. In a completely sealed container the hot water would clearly take longer to freeze than the room temperature water.

    The "boiling" sample would not actually be boiling. It might be at 100C, but it would stop boiling the instant you took it off the heat source.


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  4. #3  
    Universal Mind John Galt's Avatar
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    You may wish to google the Mpemba effect, but I found this article satisfying by its common sense approach married with sound thinking.
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  5. #4  
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    Very interesting link, John.

    When solving a problem, understanding its exact terms is as important, if not more, than knowing how to solve it.

    I hate when people try to mislead you by ill-defining the problem.

    In a closed system (with no exchange of matter), a fixed amount of water in a given container will take less time to freeze when its initial temperature is lower. There are well-known equations from which you can even calculate the time needed.

    A statement such as 'hot water freezes faster than cold water' is meaningless, because in the absence of some additional information its truth value just can't be established.
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