# Making Liquid CO2

I recently saw a video on making liquid $\ce{CO2}$: https://www.youtube.com/watch?v=8AN_XMcD3yI

Basically we seal some dry ice in a container. As the dry ice sublimates the pressure inside the container increases and so at about 5 atm we reach the triple point of $\ce{CO2}$, at which point the solid $\ce{CO2}$ melts instead of sublimating.

At some point in the video, the teacher cautions that the same experiment should not be done with a Gatorade bottle (similar to a water bottle). However, I'm not sure why this is the case.

Certainly the usual "dry ice bomb", which also has warm water poured into the sealed bottle, is not a good idea. In the present scenario, once all of the solid $\ce{CO2}$ had melted and the liquid $\ce{CO2}$ then goes into the gas phase, the increase in pressure could lead to an explosion: isn't this the same principle as in the case of the "dry ice bomb"? Is the warning because a Gatorade bottle (or water bottle, etc.) cannot withstand 5 atm of pressure?

• I'd say the plastic bottles go below their glass temperature and have very low strength in their glassy phase whereas a pyrex bottle would have thermal stability to maintain strength but I don't know the temperature involved and it would depend on which plastic a bit. It may even be chemical damage of the plastic. Commented Jul 30, 2015 at 5:21
• @user2617804 you should add that as an answer. It didn't even occur to me to consider the effects of temperature on the plastic. Commented Jul 30, 2015 at 16:00

I think these three links nicely summarize what can potentially go wrong when a plastic bottle explodes.

As for your question about how much pressure the Gatorade container can hold, that's a little trickier to figure out. It looks like the Mythbusters found that soda bottles can hold up to 150psi (~11 atm), but gatorade and water bottles aren't designed to hold carbonation, so I'm guessing they'd be closer to the 60psi (~4 atm) that they found for water coolers.

I think ultimately the answer is that the teacher is playing on the safe side: sure, you might be able to hold 10 atm of pressure in a soda bottle at home, and get some cool-looking CO2 out of it, but seeing as you could lose an eye if your bottle was even slightly damaged (and seeing that this has happened before!), is it something you'd want to let high schoolers do on their own?

• Thanks for that! I don't suppose you have any suggestions of common containers that would be suitable for such an experiment and/or simple methods of determining if a container could withstand that much pressure safely?
– John
Commented Jul 30, 2015 at 16:14

Most likely the plastic would suffers thermal and physical shock so it would shatter- that is when it suffers rapid temperature changes and rapid physical stress- plastics have very poor thermal shock resistance due to poor crack resistance and low thermal conductivity- conductivity that would stop the heat transfer occurring in one place.

If the conditions aren't rapid enough to cause shock then it probably could still fail though its hard to tell with the CO2 phase diagram (quick google search finds it) so the plastic bottles go below their glass temperature and have very low strength in their glassy phase whereas a pyrex bottle would have thermal stability to maintain strength but I don't know the temperature involved and it would depend on which plastic a bit. It may even be chemical damage of the plastic.