Re: pinhole freezing ice cream

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Sun Jun 26 2005 - 10:00:22 PDT 

Message-Id: <b7236c11e0d640893fd2bb1b66b87576@exploratorium.edu>
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole freezing ice cream
Date: Sun, 26 Jun 2005 10:00:22 -0700

Hi Laura

There is a great article on this by Don Rathjen in the ICE issue of
Exploring magazine, get a copy of the article next time you visit the
Explo.

1. Water molecules are always going from solid ice to liquid and back
again in an equilibrium at the freezing point.
Salt in the liquid phase or indeed any other molecule gets in the way
of water molecules returning to the solid phase but does not impede
them leaving the liquid phase. This shifts the equilibrium so that
there is more liquid than solid. To make the liquid from solid hydrogen
bonds must be broken and this requires energy, the energy comes from
the kinetic energy of vibration of the molecules and so adding salt to
ice lowers the temperature of the ice/water mixture.

Paul D

On Jun 26, 2005, at 9:16 AM, L. Randall wrote:

> I'm having a hard time with why the salt and ice combination has a
> lower freezing point than ice alone. Does any one have an accurate,
> simple explanation or model for what is happening?
> Thank you,
> Laura Randall
>
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