Why do candles only smoke when they’re put out?
In: Chemistry
(Solid) candle wax doesn’t burn. It has to be torn up into little molecules – then, if it’s hot enough, it will react with oxygen in the air to burn.
A candle flame is a tiny cloud of vaporized candle wax that’s super hot (that’s why it glows). When the hot molecules reach the edge of the cloud they hit oxygen and burn. This reaction heats up the cloud more and keeps the flame burning.
When a candle goes out, that little cloud gets too cold and no longer burns when it touches oxygen. You can see the vaporized wax drifting away as ‘smoke’.
This is why you need a wick, to start burning and melt the wax which is then drawn up and vaporized. The wick is protected from burning because the wax cloud keeps oxygen away from it. In the old days candlewicks would need to be trimmed every now and then, as they’d get super long and start producing too much wax vapor to burn cleanly. Candles would be super smoky after a while unless you cut the wick down. Modern candles have flattened wicks that actually curve to the side as they come free from the wax so that they poke out of the flame and burn down to a consistent length. Pretty cool technology! There are lots more cool candle facts but I’ll stop there.
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