Ms. Chemistry Pulls Through

Smart people are cool. In response to the chemistry “challenge”:

The slush phenomenon Does, in fact, occur in water. It’s just that (a) most freezers are set below the melting point of water (duh) so that the water freezes completely, therefore the water will freeze quickly into solid ice rather than a slush (the temp is not close enough to water’s melting point for an equilibrium slush state, like hail vs snow in clouds–same deal), whereas sodas have solutes which expand the range between melting and boiling points (that is, the boiling point goes higher and the melting point lower) and so what you see in a freezer as “slush” is occuring because the freezer’s temperature is close to the solution’s melting point–an equilibrium of sorts. And (b)I think that the reason it doesn’t “slush” until you open it has to do with compression and some of the gas laws you were talking about. You seemed to think that it was stupid to consider gas laws, when actually they are extremely pertinent here. The soda is full of gases dissolved via compression and also is topped by a gas that we must assume is at maximum pressure it can be without causing explosion of the container. Because factories seal things this way, there is no way for the bottle’s volume to decrease when it gets colder if it is sealed, because as the gases compress, the water in the soda expands proportionally (remember water expands as it cools–freezes), however it does not freeze because this requires energy the soda cannot access in a closed system. When you open the bottle, the action of the gas escaping allows for an energy shift, and the soda will ice down from the top as gases escape. This interesting phenomenon may even cause “trapped” gas bubbles in your beverage of choice, depending upon how much it slushes. So yes, you were partially right in thinking that the sugar (really all of the solutes, remember that there is a crap load of sodium, phosphoric acid, and other solutes) is what causes slushing in a normal, ICE-MAKING freezer. Because of its particular temperature setting. Ice freezes solid when it freezes too quickly–when there is no “flipping” back and forth between solid and liquid (as at an EQUILIBRIUM), which is why you may have heard that it can be “too cold to snow.”

These are good things to know.

[Listening to: Second Intermission – Ani DiFranco – Evolve (03:54)]