We present an undergraduate level experiment in which the radius of a rubber balloon is measured as it is cooled with liquid nitrogen.
For balloons filled with simple gases that condense at liquid itrogen temperatures, we found that the volume decreases linearly with time.
We compared our measurements with a simplified model based on elementary kinetic theory and thermodynamics that explains this behavior.
Students are encouraged to test the validity of the model by repeating the experiment using gas mixtures and gases that do not condense at liquid nitrogen temperatures.