In my lecture and on the class website Tsquare, I posted the videos of supercool

Question

In my lecture and on the class website Tsquare, I posted the videos of supercooled beer. (If you did not come to the lectures or watch the video, you can watch it now on Tsquare or have to use your imagination now.) Why isn't the bear frozen when it is chilled below the freezing point? Why does the bear become frozen instantaneously to ice when you tap the bottle really hard? What happens if you do not tap the bottle, instead put salt into the supercooled beer? Below, you find a phase diagram of CO_2 in water.

Explanation / Answer

a) Because of the carbon dioxide present.
Any solute when added to solvent decreases its freezing point. So the actual freezing point is less than the expected freezing point , so the bear isn't frozen

b)when we leave our beer in your freezer for long enough, it actually drops below its freezing temperature. However, because the inside of the bottle is perfectly smooth, there is nothing for ice crystals to form against, so the beer stays as a "supercooled" liquid for a while. When we tap the bottle against your hard surface, bubbles form, as they would in any carbonated liquid. These bubbles give the ice crystals something to "grab on to" on the molecular level, so, if you look closely, you should actually see ice radiate outwards from the bubbles throughout the liquid.

c) When sodium chloride is added to a super cooled beer there will be a freezing point depression. Freezing point depression is when a solution can be cooled below the freezing point of the corresponding pure liquid due to the presence of the solute.

d) no question

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