Question #bb37f

1 Answer
Dec 21, 2014

The deposition temperature of CO₂ at 1 atm pressure is -78.5 °C. At 20 °C, solid CO₂ is not stable unless the pressure is greater than 5000 bar.

So how could he get solid CO₂ at room temperature?

Here's that video again.

And here's the real phase diagram for CO₂.

www.cgenpower.com

The pressure inside a CO₂ fire extinguisher is 60-70 bar. This means that, at 20 °C, the CO₂ exists as a liquid in equilibrium with its vapour.

www.marineinsight.com

When you open the valve, the pressure inside the extinguisher drops.

This causes instantaneous boiling in the liquid. The boiling speed is so fast that the contents as they approach the valve are part liquid and part gas.

The energy needed to convert the liquid to vapour must come from the liquid itself. The liquid cools so fast that the temperature drops below -78.5 °C.

What you see coming out of the nozzle is a mixture of solid CO₂ and frozen water vapour that was in the air, plus invisible CO₂ gas.