Liquid Nitrogen Balloon: Charles' Law

Liquid nitrogen is poured over a balloon filled with air. The balloon shrivels as the volume of the air decreases. The balloon is pulled out of the liquid nitrogen and placed on the tabletop. It rapidly reinflates. This is a good, simple demonstration of Charles' Law, the volume of a sample of gas is directly proportional to its temperature in an expandable enclosed container such as piston or a balloon.

Curriculum Notes 

This demo is usually used when the gas laws are being discussed, but it can also be used when states of matter are being introduced.

The effectiveness of this demonstration is increased when it is accompanied by an active learning approach and by showing a computer simulation and animation of the behavior of gases at the particle level. 

Kinetic Molecular Theory Computer Simulation©2016 Gelder, Abraham, Greenbowe   Chemistry Education Resources , Oklahoma State Unversity, Oklahoma University, University of Oregon, Pearson.

https://media.pearsoncmg.com/bc/bc_0media_chem/chem_sim/kmt/KMT.php

The demonstration and computer simulation will help students explore all three levels of representation of Charles' Law, i.e. following Johnstone's Triangle, and it will help make the connection to the Kinetic Molecular Theory. The qualitative demonstration takes about five minutes to perform. Allow about 10 minutes for this demo.

Lead Time 
One day of lead time is required for this project.
Discussion 

The boiling point of nitrogen is -195.8 degrees Celsius [77.4K]. The air in the balloon is primarily a mixture of nitrogen and oxygen (b.p. -183.0 degrees Celsius [90.2K]). These absolute temperatures are between one third and one quarter of room temperature, so according to Charles' Law, one would expect the balloon to shrink by about the same proportion. It is observed in this demonstration that the balloon shrinks to much less than one third to one quarter of its original size. Therefore, we must infer that the air inside the balloon is condensing to a liquid state, which occupies much less volume than gas. Indeed, some liquid can often be observed inside the balloon as it reinflates.

Materials 
  • large Dewar flask containing liquid nitrogen
  • a balloon inflated with air
  • a large metal pan
  • tongs
  • insulated gloves
  • three small cork rings
Procedure 
  • Place metal pan on top of three small cork rings, to insulate table.
  • Place the inflated balloon in the center of the large metal pan.
  • Carefully pour liquid nitrogen from the Dewar flask over the balloon. Be careful not to let any of the liquid nitrogen splash on you or spill on your legs and feet. The balloon will shrivel up.
  • Grasp the balloon using tongs, pull it out of the liquid nitrogen, and place it on the tabletop. The balloon will reinflate to its original size.

Alternative Procedures

Carefully fill a large mouth (bass) dewar with N2 (l). One at at time, add balloons filled with air to the liquid nitrogen in the dewar. One should be able to get at least 5 or 6 balloons collapse in the liquid nitrogen. As the temperature of the gas decreases, the volume of the gas decreases. Remove balloons with tongs to show the decrease in volume of the gas inside the balloons. Demonstrate that the gas remains inside the balloon by warming the balloon back to room temperature. As the temperature of the gas increase the volume of the gas increases.

An extension of this demonstration is to distill the air. Follow the procedure by Switzer (J. Chem. Educ. 2005).

Safety Precautions 

Liquid nitrogen is extremely cold. There is a risk of frostbite if it comes in contact with your skin. Be careful not to allow it to come into contact with your skin. Be particularly careful of the liquid nitrogen as it splashes off of the balloon. It can spill off the table onto your feet and legs. Wear goggles.

Footnotes 

References

1. Oliver-Hoyo, M.; Switzer, W. L. J. Chem. Educ. 2005, 82, 251. 

Prep. Notes 
  • Liquid nitrogen can be obtained from Science Stores in the basement of Onyx building.
  • It is difficult to transport the liquid nitrogen in the dish on a cart without sloshing it all over the place. So when you retrieve this demo, if there is any liquid nitrogen left in the tray, put on the insulated gloves and carefully pour it back into the Dewar flask.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group