|Can you freeze air? And if you can, will it
freeze in layers, one layer for each type of
molecule? (e.g. oxygen, carbon dioxide etc.)
|Question Date: 2002-12-02|
Yes, indeed. A combination of low
temperatures and high pressures results in the
different components of air condensing out as
liquids. Air is about 78% nitrogen and 22%
oxygen (the remaining components are mostly carbon
dioxide, water and argon, all in very small
quantities and can be neglected). First, the
oxygen condenses into the liquid at 90.2 K (which
is negative 182.9 degrees C,) and then nitrogen
condenses into the liquid at 77.4 K (which is
negative 195.75 degrees C). This process of
condensation is in fact used industrially to
separate nitrogen and oxygen. When cooled further,
these liquids freeze into solids.
Air is made up of several different gases,
which all freeze at different temperatures. If you
were to place an air-tight box into an incredibly
cold freezer, the gases would freeze at different
times as the box cooled, and so theoretically, you
would get layers of different frozen gases.
However, there are so few molecules of any gas in
air relative to the volume it occupies, you
probably wouldn't be able to see the layers.
Instead, when you opened the box (assuming you
could do so without melting the crystals or
freezing yourself), you would probably just see a
few crystals sprinkled on the bottom of the box.
The first gas to freeze would be water vapor.
This is why the air is so dry in very cold
places. Then carbon dioxide would freeze, and then
nitrogen. The last gases to freeze would be oxygen
and argon. At absolute zero, all the atoms in the
different gas molecules would merge into one atom
(see the question this week on
absolute zero ).
For scientists living at the South Pole in the
dead of winter it can get as cold as minus 80
degrees Celsius. This makes it very hard for them
to breath outside without a special air supply. At
such cold temperatures, the carbon dioxide freezes
and drops out of the air. (Remember that it is
the amount of carbon dioxide in our blood, not the
amount of oxygen, that triggers our brain to take
a breath. The scientists would pass out simply by
"forgetting" to breathe.)
Yes, you can freeze air, and yes, each
of air will freeze at a different temperature, so
that if you were to take a jar of air and slowly
make it colder and colder, each different
ingredient would freeze into a different layer,
just as you suggest.
Water, for example
(which is often present in air as humidity),
freezes at 32 degrees Fahrenheit, or 0 degrees
Celsius. You can see this happen sometimes on cold
nights, when there is frost on the windows. This
frost is moisture which used to be in the air and
then froze in a layer onto your window. If your
windows got really cold: about -200 Celsius or
-330 Fahrenheit, then the nitrogen in the air
would liquefy on your window, and at about -220
Celsius or -365 Fahrenheit, it would freeze solid,
giving you a layer of solid nitrogen. The other
ingredients of air freeze at intermediate
The only gas which doesn't
freeze solid is Helium. It liquefies at -270
Celsius or -450 Fahrenheit, but it will never
freeze solid unless you squeeze quite hard on it.
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