|Why is it that dry ice is colder than regular
ice? What different "elements" make it colder?
|Question Date: 2004-03-13|
Regular ice is made from freezing water.
freezes at zero degrees Celsius, or +32 degrees
Fahrenheit. (Most of Europe and all scientists use
Celsius because we're lazy and it's easier, but
the US is still stuck on the Fahrenheit
"Dry ice" is made from frozen
carbon dioxide gas. Carbon dioxide is an odd
substance because at regular pressure, it is only
found in gas and solid forms: the stuff in the air
you breathe and dry ice. So when dry ice
"melts" it goes directly into the gas form! At
really high pressures, carbon dioxide does form a
liquid phase. Anyway, dry ice is much, much
colder because carbon dioxide freezes at a lower
temperature:-79 degrees Celsius or -109 degrees
It's very dangerous to handle dry ice
because it will freeze your skin and cause frost
bite in less than a minute, causing a painful "dry
ice burn". Did you know that in Antarctica, the
air can sometimes get so cold that the carbon
dioxide in the air will freeze, turning into dry
ice? This makes it very hard to breathe the
air, because without carbon dioxide, our brain
doesn't know when to make our body take a breath.
(The brain uses the amount of carbon dioxide in
our blood as a signal to breathe rather than the
amount of oxygen. Go figure!)
Dry ice is made of solid carbon dioxide
(CO2) while ice is made, of course, of
Almost all substances have a freezing
point which depends on their unique physical and
chemical characteristics. I'm not sure,though,
how well we understand why a particular substance
has the exact melting point it does.
Much of the stuff we deal with on a daily basis
is solid, meaning that it has a freezing point
(transition from liquid to solid) that is higher
than "room temperature," or about 20 degrees
Celsius. A lot of room temperature liquids, such
as water, alcohol, and gasoline have freezing
points below 20 C but, perhaps, not too far below
Substances that are normally gases at 20
C and one atmosphere pressure, such as
CO2, oxygen, and nitrogen, have much
lower freezing points. The temperature of dry ice
is around -80 C or 195 K (195 degrees above
absolute zero). Oxygen, argon, and nitrogen
freeze at around 65 K.
Neon and hydrogen freeze
at 10 to 20 K. Normal helium, as it turns out,
doesn't ever freeze exactly.
One interesting thing about dry ice is that
carbon dioxide doesn't exist as a liquid at
room temperature and one atmosphere pressure.
So dry ice doesn't melt (hence it is "dry") but
sublimates - meaning that the
CO2 goes directly from solid
to vapor as it absorbs heat. The
CO2 cylinders that are used to put
bubbles in soda are filled with liquid
CO2 but have to be pressurized at
around 17 atmospheres.
Lots of things that are gases at room
temperature can be frozen into liquids or solids
at cold temperatures. Ice is just water frozen
into a solid. Even though dry ice is called
"ice", it's not.
Dry ice is actually a gas at room
temperature - carbon dioxide - frozen into a solid
at about -110 degrees. At ice temperatures,
carbon dioxide is a gas - and as you probably know
is already in the atmosphere and air you breathe.
So if you are playing around with dry ice, you
want to make sure to be in a large,
well-ventilated room so the carbon dioxide level
in the room doesn't get to high as the dry ice
melts. By the way, -110 degrees is cold enough to
hurt you if you touch it without gloves and
definitely shouldn't be tasted (which you
Something to notice is that dry ice,
unlike water, melts directly into a gas without
being a liquid. This is called
sublimation. There are colder things than
dry ice. 70% of all the gas in air is nitrogen.
Nitrogen can freeze into a liquid at -320
degrees. Colder than that is liquid helium
which has a temperature very close to absolute
zero. Thanks for the questions.
Dry ice is carbon dioxide ice, not water
Carbon dioxide freezes at somewhere around -70 C
(I think)whereas water freezes at 0 C. Water ice
can get that cold, of course, but if you have
dry ice, it takes energy (and a lot of it) to take
something from a solid to a gaseous phase, so
it stays at that temperature until it evaporates
(carbon dioxide does not form a liquid at
atmospheric pressure, no matter how hard you
As a result, the solid stays at its evaporation
temperature. Water, by contrast, heats up to its
melting point before plateauing for the same
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