This lesson was used as a fun activity to celebrate at the end of the semester. It can be
adapted to be a lesson in refrigeration and heat engine cycles, but the outline here keeps the
scientific basis very relaxed.
Experiment Materials (per group):
- How do you make ice? (put water in the freezer and get it cold)
- So, could you make dry ice (solid CO2) in the refrigerator? Why or why not? (not cold
enough, you need something even colder)
- What about liquid nitrogen? (same as dry ice, too cold for refrigerator)
- The key idea here is that even though a freezer is very cold, low temperature, it is hot
compared to liquid nitrogen or dry ice. In other words, it is not the absolute temperatures
that are important, it is the difference in temperatures, or relative temperatures, that are
important in getting something to freeze.
To go into heat engines:
- How then to you make liquid nitrogen? (heat engine cycle, this would have to be explained. Students probably won’t know what this is.)
- Liquid Nitrogen
- Half and half
- Flavorings (mint, chocolate syrup, instant coffee)
- Food coloring
- Vanilla extract
- Styrofoam bowls (large)
- Wooden spoons
- Plastic spoons
- Measuring cups and spoons
To make approximately one cup servings: all measurements are up to taste, and can be adjusted.
It is recommended to use one part milk to every two parts half and half.
- ½ cup half and half
- ¼ cup milk
- 3 tbsp sugar
- ¾ tbsp vanilla
- approx 1tbsp of flavoring (to taste)
- food coloring as desired
Let the students mix the ingredients and flavor as they like. Pour the liquid nitrogen for
the students into their bowls a little at a time and have them use the wooden spoons to stir.
Continue adding liquid nitrogen in small portions until mixture freezes. It was found that
less liquid nitrogen is needed to make several small (one cup) servings than one large (one
gallon) batch. Roughly 10 L of liquid nitrogen is necessary to make 15 one-cup batches.
Eat and enjoy!
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