A toy balloon filled with air is immersed in liquid nitrogen and the air seems to disappear: the balloon shrinks completely. The air seems to have disappeared.
Phase transitions, gas laws.
12 to 18 years old.
Expected time for the mystery
Approximate time for teacher preparation: one hour.Approximate time in classroom: three or four individual 50-min lessons.
Liquid nitrogen requires local health and safety precautions and pupils should be supervised at all time during its use.Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials
Dewar with liquid nitrogen, toy balloons, air pump, toy balloon filled with helium gas, cryogenic gloves, syringes with one end plugged, temperature sensor, weights, supports for syringes, electric hotplate, thermal cups, glycerol, graduated cylinder (at least 60-70cm height), thin plastic tube (usually used for aquariums).
- Qualitative graphical representation of a certain thermodynamic variable in the function of another: in particular, representation of the volume of a gas as a function of the temperature or pressure.- Introduction to phase transitions.
To become familiar with the most common phase transitions, it is possible to observe what happens for water. This video shows how the phases depend on temperature: