Hydrogen Balloon Explosion Experiment

The Chemistry

Hydrogen undergoes combustion according to the following reaction:

2H₂(g) + O₂(g) → 2H₂O(g)

Hydrogen is less dense than air, so a hydrogen balloon floats in much the same way as a helium balloon floats. It's worth pointing out to the audience that helium is not flammable. A helium balloon will not explode if a flame is applied to it. Further, although hydrogen is flammable, the explosion is limited by the relatively low percentage of oxygen in the air. Balloons filled with a mix of hydrogen and oxygen explode much more violently and loudly.

Perform the Exploding Hydrogen Balloon Demo

1.  Fill a small balloon with hydrogen. Don't do this too far in advance, since hydrogen molecules are small and will leak through the wall of the balloon, deflating it in a matter of hours.
2. When you are ready, explain to the audience what you are going to do. While it's dramatic to do this demo by itself, if you want to add educational value, you can perform the demo using a helium balloon first, explaining that helium is a noble gas and therefore unreactive.
3. Place the balloon about a meter away. You may wish to weight it to keep it from floating off. Depending on your audience, you might want to warn them to expect a loud noise!
4. Stand a meter away from the balloon and use the candle to explode the balloon.

Safety

Although it is easy to produce hydrogen gas in the lab, you'll want compressed gas to fill the balloon.

This demonstration should only be performed by an experienced science teacher, demonstrator or scientist.

Wear the usual protective gear, such as goggles, lab coat, and gloves.

This is a safe demonstration, but it's advisable to use a clear blast shield for any fire-related demonstrations.