Originally Posted by
himespau
So I'm confused (like perpetually). Some have said the CO2 in the cartridges is in liquid state. For some reason, I have a vague recollection from a chemistry class somewhere saying that CO2 was never liquid, it just sublimated directly from solid to gas. Though I suppose pressure might put it in an unnatural state. Any chemistry whizzes want to enlighten me?
Liquid CO2 doesn't exist at normal atmospheric pressure. There is no temperature where it remains liquid - it will always turn into either a solid or a gas.
As you might also remember from chem, the freezing and boiling points of substances changes with pressure.
As you increase the pressure on CO2, the boiling point moves away from the freezing point creating a gap for liquid to exist.
Another interesting fact about CO2 (and similar volatile non-polar liquids) is that the pressure in a container, so long as it is not depleted (with no liquid left) or overloaded, is determined entirely by temperature, and not how much CO2 is in it. A CO2 tank at room temperature is at about 850 PSI, no matter if it is full of half empty.
Now, for the scary part, pressure increase is logarithmic with temperature. A 2x increase in the temperature of a CO2 tank results in a 10x increase in pressure, and above about 91F CO2 really doesn't want to be a liquid anymore no matter the pressure (The critical point). It's about this time when a release valve would go off if your tank was big enough to need one. Luckily small CO2 cylinders are incredibly over engineered for what they do, so you're still pretty safe.