Why does a candle not create smoke when burning but lots of smoke when you blow it out?
In: Chemistry
The heat from the flame melts the wax to a liquid then from liquid to gas before it ignites. When you blow out the candle you stop that last step from happening so the gas exists but is never ignited. You can actually relight a candle by lighting the tail of smoke.
The smoke you see is wax vapor. The flame is actually fueled by that wax vapor, so it is being burnt away while the candle is lit. When you blow the candle out it’s still hot enough that you get the wax vapor, but because there is no flame it’s not getting burnt away.
The super ELI5 answer is that when a candle is burning properly, almost all of the wax is converted into gases you can’t see. When a candle is smouldering it produces tiny particles of hot soot which you see as smoke.
The more complete and slightly non-ELI5 answer is that a candle is comprised of wax which is a hydrocarbon (i.e. comprised of molecules consisting primarily of hydrogen and carbon).
When a candle is burning properly, almost all the hydrogen and carbon is combined with oxygen and converted into gases – basically water vapour (H20) and carbon dioxide (C02).
When a candle is smouldering, just after you blow it out, it can still be producing sufficient heat to split the hydrocarbons into hydrogen and carbon but not sufficient heat for proper combustion. Particles of carbon on their own are “soot” and smoke is effectively a stream of hot soot particles.
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