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![A bunsen burner sustains its flame after the energy threshold is crossed.](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Incandescence.jpg/220px-Incandescence.jpg)
Credit: User:Debivort
Activation energy is the energy that must be overcome for a chemical reaction to occur. Here, the sparks generated by striking steel against a flint provide the activation energy to initiate combustion in a Bunsen burner. The blue flame will sustain itself after the sparks are extinguished because the continued combustion of the flame is now energetically favorable.