A candle produces a yellow flame on burning while lpg burning in a gas burner produces a blue flame. explain.
Answers
Answer:
Explanation:
You generally get a blue flame from burning wood as well, it's just usually overwhelmed by the yellow, and hard or impossible to see. Try looking at the bottom of a match just before it goes out, and you'll usually see the blue.
The blue is called "chemoluminescence". It's the light produced directly by the combustion reaction, and will therefore be present during most hydrocarbon fires. The yellow and orange (which provide most of the light from the actual fire) come from a more interesting source. When hydrocarbons burn without sufficient oxygen mixed in, they burn incompletely. This reaction produces tiny particles of solid carbon, which we generally refer to as 'soot'. The flame is full of this finely dispersed carbon, which gets heated by the combustion. A typical wood fire produces flames anywhere from 1000 K to 2000 K. At that temperature, the particles glow, giving off orange to yellow light. Those tiny bits of superhot carbon is what causes most of the light we see from fires.
Gas burners are generally designed to mix plenty of air in with the gas before it burns. so that incomplete combustion doesn't happen, soot doesn't get produced, and so all you see is the blue from the combustion. But if you block some of the air from getting into the burners, you'll find that gas flames burn just as yellow as wood
Explanation:
The blue colour of propane is caused by the second stage combustion of carbon monoxide to carbon dioxide.
It is caused by an excited state of molecular carbon dioxide that spreads its energy by collision and rotations to cause a general blue colour emission background. There are also some contributions from Swan bands. But interpret spectra with caution, spectra are often baseline corrected, and it is the background we are intereted in.
The yellow colour from burning wood is caused by soot forming in the flame, incandescent carbon particles from incomplete combustion. Soot in hydrocarbon flames is generally formed from the natural acetylene production and polymerization pathways, especially as the oxygen supply is limited. Welders know this with acetylene torches, but it is also produced from other fuels.
The hot part of the flame causes more ionisation but the reaction zone of carbon monoxide conversion is clearly emitting blue light independantly. (Did you notice the electrodes glowing in the hotter zone?)
