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From: prgclb@ihuxm.UUCP
Newsgroups: net.misc
Subject: Re: boiling hot water
Message-ID: <434@ihuxm.UUCP>
Date: Mon, 15-Aug-83 12:37:25 EDT
Article-I.D.: ihuxm.434
Posted: Mon Aug 15 12:37:25 1983
Date-Received: Mon, 15-Aug-83 20:10:45 EDT
References: <2859@decwrl.UUCP>
Organization: BTL Naperville, Il.
Lines: 27

All other conditions being equal, an ice cube tray
filled with hot water would freeze faster than
a tray filled with cold water.

It takes heat to evaporate water, so unless an
external heat source is applied (such as using a stove
to boil a teakettle full of water), the heat comes from the
liquid itself.  Loss of this "heat of vaporization"
results in a lower temperature for the remaining liquid.
(I'm sure you've all experienced this principle
at the doctor's office -- you get swabbed with disinfectant alcohol
before getting stuck with a syringe -- the alcohol evaporates quickly,
taking the heat of vaporization from your skin, leaving your skin cold.)

Hot water will evaporate faster than cold water,
resulting in more heat of vaporizaton loss,
resulting in faster temperature loss in the liquid.
Cold water, on the other hand, will evaporate very
little, and therefore has to lose its most of its heat
(and temperature) through radiation and convection,
both slower processes.

>From the armchair chemist . . .
				Carl Blesch
				Bell Labs - Naperville, Ill.
				IH 2A-159, (312) 979-3360
				ihuxm!prgclb