Friday, September 16, 2016

Seeing Liquid CO2

In the atmospheric conditions in which you tend to find humans carbon dioxide can only exist as a solid, dry ice, or as a gas. Solid carbon dioxide has the interesting property of transitioning directly to as gas when it is heated though a processes called sublimation but what if we wanted to see it as a liquid?

To turn a gas into a liquid we can do two things, cool it off (which will just give us dry ice), or you can squeeze it to increase its density. By putting some dry ice into a heavy walled plastic bottle preform it is possible to force dry ice into melting, allowing us to see carbon dioxide as a liquid. At around 100psi is is just possible to have CO2 exist as a liquid as long as you keep it around -55c (the dry ice helps), however as more dry ice melts the temperature and pressure starts to increase, if it all melts the pressure will quickly rise to over 1000psi so it is important that the tube is vented well before all the dry ice is gone.

An interesting side effect of venting the tube is that the liquid instantly begins to boil, transitioning from a liquid to a gas consumes energy and all the liquid that does not boil is frozen instead!

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