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When I swipe a matchstick, how does it make fire? Thank you. – Laura, aged 5, Brisbane, Australia
Nathan Kilah, senior lecturer in chemistry, University of Tasmania:
When you swipe a match, friction and the reaction of red phosphorus on the box to highly reactive white phosphorus provide the starting heat.
There are a lot of chemical reactions involved in the lighting of a match.
Surprisingly, the first chemical to react is not on the match, it is on the box!
This chemical is called red phosphorus. To our eyes, it just looks like a red powder. But if you zoomed right in to see how all its atoms are arranged, it would look like a bunch of triangles and other shapes stuck together into a long chain.
When you rub the match on the box, you get friction, which means you get heat. This heat causes a small amount of the red phosphorus chain to be broken apart.
When that happens, some of the red phosphorous changes into another chemical called white phosphorus. It reacts immediately with a gas in the air called oxygen. This will create a lot more heat.
So the story so far – the friction breaks the red phosphorous chain, which allows the white phosphorous to react with oxygen and the match starts to get hot.
But that’s not the end of the story.
Fuel + heat + oxygen = fire
You need three ingredients for a fire: fuel, heat and oxygen.
Friction and white phosphorus have provided the starting heat, and now the match needs fuel and oxygen to continue to burn.
The fuel comes from the sulphur (that’s another chemical) and wax in the head of the match. It also comes from the wood in the matchstick.
When it comes to oxygen, the match has a secret supply. Stored inside the match head is another chemical called potassium chlorate. When it gets hot, it releases a lot of extra oxygen and heat. This makes the match head burn quickly and strongly.
When you put it all together – the heat, the fuel and the oxygen – you get a flame! And, amazingly, all this chemistry happens in a fraction of a second.
- To read the rest of Kilah’s answer, go to the conversation.co.za
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