Why can #CO_2# be easily solidified?

2 Answers

The process of making #CO_2# actually speeds up the process of turning it from the liquid to the solid state.

Explanation:

In the dry ice industry (I hope there's one), before #CO_2# can be made into solid form (which is dry ice), it first has to become a liquid.

In reality, there are two ways of making dry ice:

The cheaper and more efficient way is by pressurising and cooling #CO_2# into a liquid. As the #CO_2# liquefies, the ambient pressure is reduced, allowing some of the liquid #CO_2# to vaporize.
As the #CO_2# vaporizes it causes a rapid decrease in temperature. This inverse temperature-pressure relationship allows the liquid #CO_2# that doesn’t evaporate to turn into a snowy substance that is compressed into dry ice blocks/pellets that you see.

The not-so-cheap but faster way is by increasing the pressure much higher than the above method and cooling the #CO_2# rapidly. This causes the #CO_2# to deposit, that is, from gaseous state directly to a solid state.

As for your statement about why #CO_2# is easily solidified, I believe it's just because humans have had more practice and done more research into solidifying #CO_2#.

Apr 2, 2018

It's not that easy to solidify it... In fact, I would say it is HARDER to solidify #"CO"_2# than water...


Let's ACTUALLY look at the phase diagram:

http://ch302.cm.utexas.edu

How dry ice is usually made is that it is pressurized into a liquid at typical cold temperatures (#0^@ "C"# is doable), and then cooled down to cryogenic temperatures to get it into a solid.

https://www.continentalcarbonic.com/

That means we first move UP the phase diagram from a gas to a liquid, and then LEFT from a liquid to a solid.

It's not to say that is easy... but after releasing the dry ice into normal atmospheric pressure conditions, it spontaneously will sublime, crossing the solid-gas coexistence curve rightwards at the #(P,T) = (1color(white)(.)atm,-78.5^@ C)# point.