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Water Equilibrium of Melting and Freezing
By Juliet Myfanwy Johnson
Freezing
The freezing point of water
is 0 degrees Centigrade (32 degrees Fahrenheit).
More accurately, 0 degrees
is the point at which water is melting at the same rate it is freezing,
creating a balance.
At 0 degrees, water
molecules are moving very slowly, and a solid begins to form out of the water,
which is ice.
How Does Salt Affect the
Ice?
When the water has reached
an equilibrium at 0 degrees, the ice, undisturbed, will remain ice.
If any foreign substance is
added to the ice like salt, the water molecules can't attach to form ice as
quickly, and so the freezing point (or ice formation rate) is lowered, while
the melting rate is unaffected.
So, ice is forming less
quickly, with the salt disturbing the process, and melting is continuing.
Because of the lower
freezing point, the rate of melting has continued, while the rate of freezing
has slowed. So, water begins melting before it can form more ice.
Salt is Not the Only
Solution
Any foreign substance can
disturb the equilibrium of melting and freezing water molecules at 0 degrees
Centigrade.
Alcohol and sugar, among many
other common substances, will have the same affect.
Salt is used to help melt
ice on roadways because it is cheap and abundant.
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