Date: Thu, 20 Nov 1997 21:05:32 -0800
Message-Id: <v01520d02b09a456ccef1@[205.179.255.161]>
To: pinhole@exploratorium.edu
From: mafifi@redshift.com (Marc Afifi)
Subject: Re: MP/FP
>Can anybody out there explain the exact difference between a freezing
>point and a melting point? Are they the exact same temperature (like 0
>degrees for water)?
>
>What about a millionth of a degree above zero, wouldn't that (or even
>less than that) be the melting point of water?
>
>Ian Bleakney
It occurs to me, and I may be wrong as I have been so many times before,
that the definition of melting point is the temperature at which the solid
and liquid phases are in equilibrium. Coincidentally, this is also the
definition of the freezing point. Ipso facto, they are the same
temperature. Not a millionth of a degree above, nor a millionth of a degree
below. Exactly the same temperature. This is the only temperature at which
the two can exist in equilibrium. If the temperature is even slightly above
the MP/FP (even a quadzillionth of a degree) some of the solid will absorb
the energy by melting. This will cause an increase in the amount of liquid.
On the flip side (and almost everything I say is flip), if the temperature
is even a quintillionth of a degree below the FP/MP then some of the liquid
will solidify to release energy to compensate for the excess energy. So,
melting point and freezing point are the SAME temperature, it just depends
on which way you look at it. Is the solid heating up? Ore is the liquid
cooling down? That's how we decide if it's a melting point or a freezing
point. Heating up = melting point. Cooling down = freezing point.
For a more in depth discussion of equilibrium, ask another question. (At
your own risk!)
-Marc
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Favorite Oakland Raiders motto: Marc Afifi
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