|If you melt dry ice, can you swim in it without
|Question Date: 2003-05-15|
If you melt dry ice, can you swim in it without
Dry ice isn't frozen water- its
frozen carbon dioxide, and it "melts" directly to
carbon dioxide gas, so there will be nothing to
swim in. Most chemicals can exist as solid,
liquid, or gas, and which of these three forms a
chemical takes will depend on temperature and
pressure. The temperature and pressure dependences
are different for each chemical. For example: at
atmospheric pressure, water is solid below 32
degrees F and gaseous above 212 degrees F. On high
mountains the air pressure is less, so water boils
(becomes a gas) at lower temperatures- this is why
things take longer to cook at high altitudes. High
in the upper atmosphere where pressure is very
low, water's boiling point is actually reduced all
the way to its freezing point, so liquid water
cannot exist. With carbon dioxide this critical
pressure is much higher than atmospheric pressure,
so liquid carbon dioxide cannot exist out in the
open, even at sea level.
It must be kept in a
As it turns out, there isn't really any way to
melt dry ice under normal circumstances. Let's
explain: the state of matter, gas, liquid, or
solid, basically depends on its temperature and
also the pressure. By pressure, I mean how much
force is pushing on it from all sides; we feel
pressure from the atmosphere all the time. In
fact, if we left the earth's atmosphere (like on a
space walk without a space suit), our skin would
probably be damaged from trying to hold us
together without air pressure to help (among other
things -- the reduced pressure might also cause
our blood to start turning to a gas -- good
reasons for space suits!).
Dry ice is
carbon dioxide, CO2, which is a gas at
room temperature and atmospheric pressure. If you
stay at atmospheric pressure but make
CO2 cold, it goes straight to dry ice
-- solid -- instead of becoming liquid.
is no liquid form of CO2 at atmospheric
pressure. I'm not sure, but I suspect you might be
able to get liquid CO2 if you increased
the pressure, though I doubt you would feel "wet"
from it if you could stick part of yourself in it.
To learn more about how CO2 goes
straight from solid to gas, try looking up the
Dry ice is called dry ice because the solid turns
to gas when heated, without turning into a liquid
first. However, if we apply pressure and heat, we
can turn it into a liquid, and sure, we can swim
in it. We know this because of something called
the phase diagram of carbon dioxide (the "stuff"
of dry ice). It will be cold though !
You cannot swim in melted dry ice because dry ice
(frozen carbon dioxide gas) does not melt.
Instead of melting, dry ice "sublimates",
which means it turns straight from a frozen solid
into a gas. If you tried to jump into a pool
filled with carbon dioxide gas, first you'd hit
the bottom of the pool and then you'd suffocate.
It is true that most compounds have three phases
-- solid, liquid and gas. However, for some
compounds, one or more of those phases only occurs
at special pressures. Carbon dioxide is a solid
and a gas at normal (atmospheric) pressure
depending on the temperature, but is a liquid only
at very high pressures. These are pressures you
and I would normally never experience, and so we
will probably never see liquid carbon dioxide.
Where would you expect to find really high
pressures on the earth?
Molecules and atoms exist in certain physical
forms (solids, liquids, and gases) on earth
because of the temperature and pressure that the
earth has. The temperature and pressure varies
depending upon where you live. But most molecules
(except water) and atoms are in the same state no
matter where on earth you are. For instance,
carbon dioxide (CO2) is always a gas
when in the earths atmosphere. Carbon dioxide is a
gas, unless it is cooled down to really low
temperatures and under a lot of pressure. Dry ice
is solid CO2. It is solid because it is pulled out
of the air when the air gets reallyyyyyyy cold
(way colder than the north pole), and reallyyyy
high pressure. Once the CO2 is a solid,
it stays like that until you bring it out in the
earths atmosphere. Then you see it start to
"smoke". This is when it is going back to its
normal state (gas) in the earths atmosphere.
This process is called sublimation, which
means that the molecule goes straight from the
solid form to the gas form. Most molecules melt,
where they go from being a solid to a liquid.
Although it is possible for dry ice
(CO2) to be a liquid, it would never
exist like this under "normal" atmospheric
conditions. So although it may be possible to get
liquid CO2, you could never swim in it
because it would be wayyyyy to cold for you to
survive. And if you did swim in it, you most
certainly would be "wet".
If you melt dry ice, can you swim in it without
getting wet? If you melt dry ice at normal
atmospheric pressure -- you only get gas since
liquid carbon dioxide has such a high vapor
pressure. If you did your experiment under
pressure -- say at the bottom of the ocean, it is
possible to get a liquid, but you'd probably not
want to swim in it, as you'd freeze very quickly.
It might be possible to find a solvent in which
you could dissolve a lot of CO2 (e.g. several
liters of acetylene can be dissolved in a small
amount of acetone) but it would still require
pressure and still be fairly uncomfortable.
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