Beer Freeze

This helps kids see the effects of temperature and pressure and phase changes in a dramatic fashion.

Now, I use any CLEAR glass bottled beer. These include MGD (Miller Genuine Draft), Corona, Sol, and a few other really terrible beers. Keep in mind, you are going to destroy the beer, so using a good beer would be a sad thing, indeed. For those of you who can't get away with using a beer in your classroom, a clear glass sparkling water thing works as well. Try to keep with GLASS containers, tho. The plastic containers actually change volume with the freezing liquid and throws in another variable along with the P and T.

Method 1: Quick & Easy for PhySci folks.

  1. Toss a MGD, or similar, in the freezer for about 30 minutes. If your freezer is REALLY cold, it may takes less time. Practice this. If it's WAY too cold, it'll freeze solid with the possibility of exploding. If it's way too warm, nothing'll happen.
  2. Remove the MGD, or similar, and have kids observe it. It should look just like it did before chilling. Liquid, refreshing, less filling...
  3. Crack open the cap and quickly observe! If it is near the right temp, you will notice dendrites of freezing starting at the neck of the bottle and flowing downward till most or all the beverage is solidly frozen.
Method 2: More fun for the Chem folks.
  1. Set up a rock salt bath similar to the one needed for making ice cream in class.
  2. Place the beverage of your choice inside this rock salt bath for 20 or so minutes. This usually is, depending upon your salt concentration, about -6oC.
  3. Remove the MGD, or similar, and have kids observe it. It should look just like it did before chilling. Liquid, refreshing, less filling...
  4. Crack open the cap and quickly observe! If it is near the right temp, you will notice dendrites of freezing starting at the neck of the bottle and flowing downward till most or all the beverage is solidly frozen.
What has caused this? Well, my inquisitive furry friend, the sealed bottle's envoronment has a specific volume, pressure, and temperature. By changing one, you are necessarily affecting the others. The chilled liquid has a smaller temperature, esentially the same volume, thus a smaller smaler pressure. This is, of cousre, according to the basic gas-law, PVNERT. Better known as PV=nRT. Even though the internal pressure has decreased, it is still far greater than the pressure outside the container, namely one atmosphere. Upon opening, the pressure inside drastically plunges as it tries to equalize with the atmosphere. This rapid decrease in P corresponds to a rapid decrease in T, since the V is essentially the same. This rapid drop in temperature of a liquid that is NEAR freezing actually plunges the liquid into a frozen state. Cool, huh? No pun intended...


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