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Q & A: Why does blowing put out a flame?

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Most recent answer: 11/03/2014
Q:
If fire needs oxygen, then why blowing on a candle extinguishes it? If I blow on embers, they start to glow, but on a candle flame, it kills it. Why?
- Anonymous
A:

That's a great question.

As you figured out, blowing on the embers increases the rate they burn, by getting more oxygen to the site where oxygen reacts with the carbon compounds.

What happens with the candle? The candle already has a lot of oxygen available. What's limiting it is the flow of evaporated wax up into the flame. That flow is driven by the heat given off by the flame itself. When you blow, you cool down the gases and the surface of the candle and spread out the wax vapor.   So when you blow on it, there's no longer a region which has enough wax molecules in it and also is hot enough to get the reaction to occur. The surface of the candle has plenty of wax, but it isn't hot enough. The gas may now not either be hot enough or have dense enough wax vapor.

Mike W.


(published on 11/03/2014)

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