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Re: cooling water



Richard W. Tarara wrote:

The various references that have been given on this topic all lead to the
same ultimate conclusion. If you put _equal masses_ of hot and cold water
in the freezer, you will end up with a smaller mass of ice from the hot
water. Under the right conditions, this hot water may well freeze before
the cold, but to end up with equal masses of ice, then simple Calorimetry
will dictate that the hot source will take longer than the cold. To do
this, you'd have to start with more hot than cold since evaporation seems a
major component in the process.

So your experiment needs to precisely measure the masses both before and
after freezing.
Which is why it is important to closely examine the phrasing of a
claim before debunking it. The claim that is usually phrased that you can
freeze a bucket of hot water faster than a bucket of cold water - and if there
is no lid on them then due to evaporation, you often can. The stuff about
masses being equal at the end is presumptions of the listener.

Another factor that I've heard plays a role is that water that has been heated
will contain fewer gases that inhibit the cyrstallization. This gives the hot
water another slight advantage. This may be the dominant factor in the related
claim that hot water pipes freeze faster than cold water pipes. In this case
the system is somewhat closed, so evaporation is not as likely - but water
sitting in a hot water pipe and water sitting in a cold water pipe will have a
similar starting temperature (if the taps have been off for a while).


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| Doug Craigen |
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| If you think Physics is no laughing matter, think again .... |
| http://www.cyberspc.mb.ca/~dcc/phys/humor.html |
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