Chemical Concepts Demonstrated: Hydrogen/oxygen chemistry, activation energy
The hydrogen whistle reactor consists of:
Remove the rubber stopper, light the match, and ignite the hydrogen gas.
There is a slight whistle present as the flame at the top burns. Eventually, there is a loud bang from the bottom of the reactor.
The flame overcomes the activation energy necessary for the reaction between hydrogen and oxygen. However, in order for this reaction to occur violently, hydrogen gas must be consumed.
During the course of the reaction, the hydrogen is used up and air rushes into the reactor via the large hole at the bottom (this produces the whistling noise). As the reaction proceeds, the ratio of hydrogen to oxygen will hit one of the three values that allows the hydrogen to react with the oxygen in the air fast enough to produce an explosion.