Why does a candle make no smoke when it is lit but makes a lot of smoke when you blow it out?
In: 5243
The flame of the candle is actually melting, vaporizing, and then burning the wax (not just the wick!). When the flame goes out, it’s no longer burning the wax, but the heat is still hot enough to vaporize the wax until it cools a bit. So the “smoke” is actually wax vapor
It’s not smoke. It’s wax vapor.
Solid wax can’t burn.
Liquid wax looks like it can burn, but in fact, it can’t. Only wax vapor can burn (mixing with the oxygen of the air).
When you put a flame on the wick, it melts the wax in the wick, but it vaporises some too. That vapor instantly catches fire (because the flame of the lighter is there).
The heat from the burning wax vapor melts some more of it, vaporises some more of it, which burns because there’s a flame, and it’s a cycle.
You interrupt the cycle by blowing the flame away.
The wax is still hot enough to evaporate a bit, but that vapor doesn’t have a flame to light it, so it just slowly rises in the air, looking like smoke.
A few seconds later, the liquid wax isn’t hot enough to evaporate anymore. No more “smoke”.
If this were true, then putting a flame in the “smoke” would make it catch fire, proving it’s not smoke. You can do that experiment.
1. Light a candle
2. Light a lighter, put its flame above the candle
3. Blow the candle out (without blowing the lighter out)
4. As soon as you see smoke, make it run through the lighter.
This should make the smoke disappear. In some cases, the fire will run back from the lighter, along the smoke-path to the wick, and relight the candle. Cool shit.
Candles produce smoke even when burning. A yellow or red flame is relatively cool (for a flame), and will not completely burn all its fuel. You may have seen a blackened empty jar candle, this is soot that was produced by an incomplete burn. Search for “candle soot jar” if you’ve not seen this before. Jars will get this soot even if the candle was never extinguished.
A candle burning for 1 hour produces the equivalent amount of smoke as 1 cigarette.
As others have noted, the “smoke” you see when you extinguish a candle is not actually smoke, but wax vapor. You can even relight the candle by setting the vapor on fire. The flame will burn back to the wick and start releasing more vapor to keep the flame burning.
Because the smoke is what is lit in the first place. It is vaporized wax and when you blow it out you take away a portion of the fire triangle away causing the reaction to halt, and the result is what would have been burning wax vapor as smoke until the heat drops and then the smoke stops too
I see people commenting on complete vs incomplete combustion, which is correct. But I haven’t seen anyone mention the reason for a candle have complete or near complete combustion. The key is a term “laminar flow”. the candle wick allows fuel and oxygen to be drawn into the reaction zone in the perfect ratios. This makes the reaction self regulate and create a calm updraft. As long as that updraft is relatively undisturbed the reaction will maintain the rate. Disrupt the flow and the reaction air to fuel mixture is off an now you don’t get perfect, self regulating combustion.
Latest Answers