How does air pressure affect the freezing point of water?

Answer 1

It does not very significantly because melting does not involve gas-phases molecules. Boiling, on the other hand, is strongly affected.

See the Related Questions for how the boiling point of water is affected by air pressure.

Answer 2

Generally, the melting point of a substance increases as the pressure increases. There are some notable exceptions, however, water being one.

Yes, it does have an effect, but it is a small one (not nearly as large as the effect on boiling points for instance). This is because the volume change from solid to liquid is not usually very large for most substances (again, as opposed to liquid to gas transitions), and the atmospheric pressure is mostly an effect due to this volume change. Therefore it does have an effect, but unless the pressure is very extreme (either very high or very low), the difference will be very small.

Answer 3

Lower pressure allows the molecules in a solid to expand the distance between themselves, and to become more active. This is the same as the effect of raising the temperature. If you lower the pressure enough, you can make the molecules so active that they become liquid, without ever adjusting the temperature. You are, in effect, lowering the melting point by lowering the pressure.

However, many substances, at sufficiently low pressures, completely skip the liquid state and got directly from solid to gas. This is called sublimation. It is readily obervable with carbon dioxide because atmospheric pressure is below the sublimation point of carbon dioxide. Dry ice, which is just frozen carbon dioxide, does not melt at all, but goes directly from a solid to a gas.

My point is, if you lower the pressure enough, you completely do away with the melting point.

Added:

In 'Related links' attached to this page (lower left corner) a diagram-picture of

"Melting point: Temperature and Pressure" is shown as

Green line for most 'normal' solids

and of

Water-Ice: it is the Green-Dotted line.

Answer 4

A decrease in atmospheric pressure will cause a slight increase in the freezing point. Beginning at 0 degrees Celsius at pressure point of 1 ATM, it will increase to 0.01 Celsius at 0.006 ATM. Known as the tripple point of water, temperatures below this will always be frozen.

Answer 5

Well, I've experienced a wierd event in the dead of winter last year; At 12F there was liquid water in my car's plastic (PET) water bottle... I had drank about 1/3 of the bottle the evening earlier, then resealed it with the bottlesomewhat crushed. This "crushed" condition must have kept the contents in a reduced pressure state. The water was at 12F and still liquid. Upon removing the sealed cap, the (and the bottle regained it's shape, the contents quickly became solid before my eyes in a few seconds. Cool!

Answer: The freezing temperature of water while in a reduced pressure state can stay liquid below 32F... I've seen 12F. (This was drinkable... bottled water, it may not be "pure" H2O.)

Answer 6

pressure does not effect the melting points of solids because pressure has nothing to dowith the intermolecular space of matter. if it could effect then the heavenly bodies as such they seem they couldn't be seem so.

Answer 7

The greater the pressure, the higher the melting point.

The same as for the boiling point.

Answer 8

as pressuse increases the melting point of ice decreases

Answer 9

Yes, generally as pressure increases the melting point increases.

The only exception to this is water, for which the opposite is true: increased pressure lowers the melting point.