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Q:
Why does the needle valve in a bunsen burner remain cool? And also, what kind of energy is released by the reaction between the gas and the oxygen in the air when a bunsen burner is used?
- Clarissa (age 14)
Anglec JHS, USA
A:
The needle valve in a bunsen burner is not right near the flame. The
flame burns where the gas and air (with oxygen in it) mix, in the
hollow tube held above the needle valve. In addition, the needle valve
is below the flame. The burning gases already are moving upwards
through the tube because the gas comes out of a jet at the bottom
pointing up into the tube. So all the hot gas comes out of the top of
the tube, in a nice, controlled fashion and there is no "flickering" of
the flame and little chance that there will be unburned gas at the end
of the reaction.
There may be a little warming up of the needle valve in a bunsen
burner when it operates because the flame emits visible and infrared
light in all directions, some of which goes downwards towards the valve
and gets absorbed. But air comes in from the sides to mix in with the
gas (the Venturi effect, using Bernoulli's principle), and this flowing
air helps to keep the bottom of the burner cool.
Tom
(published on 10/22/2007)
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