If dry ice melts into a gas, how does it become a solid?

Answer 1

Technically, Dry Ice "Sublimes" into a gas. Melting would imply it turns into a liquid.

In order to make dry ice, Carbon Dioxide (CO2) is cooled under pressure until it reaches the solid state.

It is possible for Carbon Dioxide to be a liquid, although, not under normal atmospheric condictions.
Looking at the phase diagram of CO2,
http://scifun.chem.wisc.edu/chemweek/CO2/CO2_phase_diagram.gif
You must put CO2 under quite a bit of pressure before it will liquify at any reasonable temperature.
Also from the phase diagram, you can see that at room pressure (~1 atm, 25 degrees C), you can see why dry ice goes directly into the gas state as its temperature increases.

Answer 2

Dry ice is solid supercooled Carbon Dioxide (CO2) gas. When the CO2 gas is cooled to 78.5 degrees celsius, it forms a solid. It is not stable in liquid form, therefore when it is in the solid state and is heated it sublimates directly to gas form. When that gas is cooled back down it forms a solid again.

There are places in the world where water sublimates directly into gas, i.e.- at the top of mt kilimanjoro.

Answer 3

It is generally compressed and cooled at the same time to form a solid. CO2 can exist as a liquid but not at normal pressures. Under moderate pressure like in a compressed gas cylinder it can exist as a liquid.

Answer 4

Dry ice, or solid carbon dioxide, has no liquid state.
In fact, its state transitions have entirely different terms:
--- Solid ==> Gas = Sublimation
--- Gas ==> Solid = Deposition

Answer 5

dry ice sublimates into a gas. CO2 cannot exist as a liquid at normal pressures. It is frozen by cooling and pressurizing it.

Answer 6

It doesnt become LIQUID at normal pressures. Dry ice (frozen carbon dioxide) is sublime. If you increase the pressure enough you can get a liquid.

Answer 7

Pressure. Lots and lots of pressure.