Chemistry

What is a flame?

Flames from a bonfireFlames from a bonfireWe are all familiar with flames, the flickering tongues of coloured light that ripple upwards from bonfires and burning candles. Flames are the visible portion of hot gases that are produced when something burns. Only the hottest portion of the gases emits light, and it is this portion that we see as coloured flames. The cooler portion of the gases remains invisible.


Lighting a candleLighting a candle

Burning

To get something to burn (the scientific term is “combust”), oxygen, fuel and a source of heat are needed. The heat comes from striking a match, or focused light, or something else that is already burning. A candle is lit by lighting its wick, the cord sticking out of the top, with a match or a lighter. The rest of the candle is made of wax. The wax contains atoms—the basic building blocks of matter—of the elements carbon and hydrogen. They are the fuel for the combustion process. 



Blue flames from the burning of gas on a cooking ringBlue flames from the burning of gas on a cooking ring

Glowing gas

On Earth, gravity determines how the flame burns. The hot gases in the flame are much hotter than the surrounding air, so they rise upwards. This is why flames are "pointed" at the top. If you were to light a fire in a place where gravity was very low—on a spaceship, for example—the flame would form a sphere.

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