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Name: Karen
Status: Other
Age: 40s
Location: N/A
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Does altitude change the freezing point of water?

By itself? If you put the water in a sealed, insulated container and lofted it in a balloon? No. Altitude by itself is a measure of how far away from the Earth's center you are, which in turn means how strong gravity is. Gravity has very little influence on the freezing point, because water is essentially incompressible.

However, you probably mean freezing in an open container, exposed to the surrounding atmospheric pressure. In that case the answer is: yes, for several reasons. First of all, the freezing point of water increases with a decrease in the pressure applied to it. Hence the freezing point of water will be less at high altitude and low pressure. But this effect is small. The freezing point of water rises a mere hundredth of a degree per atmosphere of decrease in pressure.

It is also true that water collected at high altitude, for example water droplets in high-altitude clouds, is exceptionally pure. This water will not freeze easily, because ordinarily water needs some ``seed'' to grow a crystal of ice around. That seed is commonly a speck of dirt or the walls of the container, but there isn't either at high altitude, so liquid water droplets exist up there down to ridiculous temperatures, -40 or so I believe.


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