Witnessed Supercooled Liquid Phenomenon

[RJ Emery]

I had a two liter soda bottle stored outside in the cold. When I retrieved it, the contents was still liquid. Upon opening it, however, when the CO2 bubbles began to escape, the entire contents froze almost instantly around the bubbles. I am curious about what phenomenon I witnessed.

 

[Vanadium 50]

As the CO2 goes out of solution, the melting point rises. When the melting point exceeds the temperature, it freezes.

 

[RJ Emery]

As the CO2 goes out of solution, the melting point rises. When the melting point exceeds the temperature, it freezes.

How can a gas have a melting point? It is driven into solution by pressure and comes out of solution when that pressure is released.

Solids have a melting point, and when that point is reached, a solid becomes a liquid. Not so for a gas.

 

[Vanadium 50]

The solution has a melting point. Or a freezing point. It's the same thing.

 

[TumblingDice]

How can a gas have a melting point? It is driven into solution by pressure and comes out of solution when that pressure is released.

Solutions are homogenous mixtures. When in solution, the CO2 is dissolved on a molecular level. The melting point V50 referred to was that of your soda (the stuff that froze), not the CO2 that escaped. The melting point of the solution was lower before the CO2 escaped.

 

[sophiecentaur]

How can a gas have a melting point? It is driven into solution by pressure and comes out of solution when that pressure is released.

Solids have a melting point, and when that point is reached, a solid becomes a liquid. Not so for a gas.

Try to avoid getting hung up on simple definitions of states. Despite what we learn at school, many substances are not simple solids, liquids or gases. (Peanut butter, whipped cream . .. . . )
CO2 is just a compound and the molecules will behave according to what's going on in their immediate vicinity. Free CO2 has CO2 molecules around it and does not 'stick to them' at temperatures in a freezer (it is gaseous). It is the mixture of CO2 and H2O that behaves as a liquid at sub-zero temperatures - not the CO2. When the molecules are in amongst water molecules (solution) their presence affect the intermolecular forces of the water molecules and alter the temperature at which the mixture goes solid.

The boiling and freezing temperatures of mixtures are usually different from those of the pure substances. We use salt on roads and Glycerol in engine cooling systems (anti-freeze) for this reason. 'Anti-freeze' also raises the boiling point of engine coolant, btw, so it is useful in two ways.