Reaction of Hydrogen and Oxygen

What it shows

The chemical reactivity and flammability of different gases is demonstrated by exploding the balloons with a lit candle.

How it works

Helium, an inert gas, just pops because it does not chemically react with oxygen. Hydrogen reacts with oxygen in air, producing a large yellow fireball and a loud bang according to the following chemical equation:

2 H₂(g)  +  O₂(g)  →  2 H₂O(g)

But when a 2:1 stoichiometric mixture of hydrogen to oxygen is exploded, there is a big sound contrast from the hydrogen only balloon. The rapid release of energy causes a quick combustion of the surrounding gas which makes the bang a lot louder and sharper.

Setting it up

You can choose which balloons to do. The usual progression is He, then H₂ only, ending with H₂ and O₂.

Safety: Put on eye protection, ear protection, and a lab coat. Warn the audience of loud boom sound and have them cover their ears. Provide hearing protection for anyone (young children/babies) who can't cover their own ears. Make sure the balloons are well separated so that you don't accidentally set off one with another. Also make sure there is enough space all around the exploding balloon.

Inflate the balloons and attach with some type of string (monofilament or ribbon) to weights to keep them from flying away. Tape a candle to a long yardstick (2 meters is recommended). Make sure you have your safety gear on, especially your ear protection! Light the candle and touch the flame to the lower side of the balloon. Don't touch the very bottom, or you will burn through the string and lose the balloon!

Here is our color coding scheme: Green balloon with helium, blue balloon with hydrogen, red balloon with hydrogen and oxygen mixture. You can also have a balloon with hydrogen and air - this is less of a boom than the 2:1 hydrogen and oxygen balloon, and you can have your students discuss why.