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anonymous

  • 4 years ago

When methane is burned, why do the waste gases contain carbon dioxide and nitrogen?

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  1. anonymous
    • 4 years ago
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    The CO2 is a product of the combustion: CH4(g) + 2 O2(g) = CO2(g) + 2 H2O(g) The N2 will only be there in the waste gas if it was already present in the feed gas, since it is neither consumed nor produced by the chemical reaction. If you burn methane in air, which is a mixture of N2 and O2, then you could get N2 in the exhaust -- because it was present in the feedstock.

  2. anonymous
    • 4 years ago
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    Can you possibly make that simpler?...

  3. anonymous
    • 4 years ago
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    You get carbon dioxide (CO2) from the chemical reaction between methane and oxygen (O2), if you burn methane in air. Since air contains nitrogen (N2) gas, the exhaust gas from the reaction will still contain the nitrogen (N2). It depends a little on how you do the burning -- whether you mix the methane with air, or just with pure oxygen. You didn't say how you were burning the methane.

  4. anonymous
    • 4 years ago
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    Its in a kiln and methane and air are put into it, so it would include nitrogen. Thankyou!!:)

  5. anonymous
    • 4 years ago
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    OK. One factor that is relevant, then, is that at very high temperatures the N2 and O2 in the air can combine to form various compounds of nitrogen and oxygen (NO2, NO, N2O5 et cetera) that are generically called NOx (the x stands for any of the possible subscripts). Many of these compounds are obnoxious and form a major component of air pollution. Hence, many air pollution regulations center around reducing NOx emission by high-temperature combustion processes, such as occur in car engines. I doubt whether kilns are subject to the same regulations, if we're talking about craft kilns, but if we are talking about big industrial kilns, then certanily there are regulations.

  6. anonymous
    • 4 years ago
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    Im only doing my GCSE's!!! i cant understand that:L

  7. anonymous
    • 4 years ago
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    Sure you can. Let's just break it down a bit. Air is a mixture of nitrogen gas (chemical formula N2, meaning each molecule of air is made of two nitrogen atoms joined by a chemical bond) and oxygen gas (chemical formula O2, same idea). Methane is a compound, each molecule of which is made of 1 carbon atom and 4 hydrogen atoms, chemical formula CH4. To "burn" something means to mix it with oxygen and air and make a chemical reaction happen. In this case, the reaction that happens between methane and oxygen is that the hydrogen atoms all get ripped off the carbon atom and attached to oxygen atoms. In the process, the oxygen molecule is broken in half. Furthermore, two oxygen atoms now attach themselves to the bare carbon atom, in the process breaking up yet another oxygen molecule. We write a chemical equation to describe the whole process: CH4(g) + 2 O2(g) -> CO2(g) + 2 H2O(g) The numbers in from of the chemical formulas just tell us how many molecules are involved. One methane molecule combins with two oxygen gas molecules to give one carbon dioxide molecule plus two water molecules. (The water is what you get when oxygen attaches to hydrogen atoms). So that's the chemical reaction that actually happens, when you burn methane in air. It turns out that when you allow the chemical bonds between carbon and oxygen, and between oxygen and hydrogen, to form, you release a lot of energy, much more than you consume breaking up the bonds between carbon and hydrogen, and between the oxygen atoms in the O2 molecule. So this reaction produces a lot of heat. Things get hot. Now it turns out when things get very hot -- very high temperatures -- then it's possible for the nitrogen and oxygen in the air to react with each other. For example, like this: N2(g) + O2(g) -> 2 NO(g) One nitrogen molecule and one oxygen molecule have been ripped in half to form two nitric oxide (NO) molecules. Now, NO is a pretty reactive molecule. It is very happy to attack lots of other molecules and react with them. For example, it can attack oxygen and water molecules in the air like this: 4 NO(g) + 3 O2(g) + 2 H2O(g) -> 4 HNO3(g) That last compound, the result of this reaction, is nitric acid. From the name, you'd guess this to be nasty stuff -- and you'd be right. Like all acids, if it gets in your eyes, it will burn, and if it gets on your skin or into your lungs, it will irritate them. So this is one source of the nasty effects of air pollution: the combustion of something like methane produces enough heat to make the nitrogen and oxygen in air chemically combine, and some of those compounds can react with harmless compounds in the air to produce the harmful compounds of air pollution. How's that?

  8. anonymous
    • 4 years ago
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    Let me add all this stuff about NOx and air pollution has nothing to do with your original question! I just added it because it's an interesting secondary topic related to your question.

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