 
Combustion is what happens when a fuel combines with oxygen.When a candle burns, wax molecules combine with oxygen molecules from the air. Combustion just means burning. Combustion is an exothermic reaction. Usually when something burns, some things happen:
The reason things burn is that they contain energy, stored in the molecules. Lighting a fire with a match is like opening a small hole in a dam ... all the energy of the wood can escape, once some of it starts to get out.Combustion can happen slowly, like when you burn wood. Or it can happen very fast, like when gasoline burns, or natural gas vapours explode. Here are some ways we demonstrated combustion in the classroom: 
First we obtained some magnesium metal. This whitish metal has an unusual property:it burns really brightly.
The metal burns quickly, gives off a bright white light, and leaves behind some ash. Can you think of some uses for a metal like this? How about making rescue flares, in case you're lost!  The next thing we did was to fill a large plastic jug with ethanol vapour.Just like gasoline fumes, this gas explodes when a flame is applied. It does combustion really fast. After putting a small amount of liquid into the jug and allowing the fumes to fill it, we emptied the remaining liquid, and then breathed into the jug to make sure there was oxygen in there too. Things won't burn unless there is oxygen to combine with. Then a spark was added, to start the gas burning.  Here's what we saw. The gas burned very quickly, giving off a huge blue flame, and a loud pop. Thanks Sylvie for the demo |