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| thyristor |
 Posted: Sat Jun 21, 2008 8:14 am Post subject: Combustion |
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Forum Sophomore
Joined: 11 Feb 2008
Posts: 190
Location: Sweden
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How come that for example wood can burn in oxygen when the oxygen is bound in molecules where both molecules have noble gas structure (in this case 8 valence electrons)?
I've been thinking about that maybe the only need for heat, when initiating a combustion, is to split up the oxygen molecules so that they can react with what's going to be combusted. Is this true?
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| Bunbury |
| Posted: Sat Jun 21, 2008 10:30 am Post subject: |
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Forum Ph.D.
Joined: 26 Sep 2007
Posts: 850
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That's an excellent question and one that I couldn't answer. According to Wiki it's much more complicated than just splitting the molecule into two atoms.
http://en.wikipedia.org/wiki/Combustion
Scroll down to Reaction Mechanism section.
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| The high energy required for initiation is explained by the unusual structure of the dioxygen molecule. The lowest-energy configuration of the dioxygen molecule is a stable, relatively unreactive diradical in a triplet spin state. Bonding can be described with three bonding electron pairs and two antibonding electrons, whose spins are aligned, such that the molecule has nonzero total angular momentum. Most fuels, on the other hand, are in a singlet state, with paired spins and zero total angular momentum. Interaction between the two is quantum mechanically a "forbidden transition", i.e. possible with a very low probability. To initiate combustion, energy is required to force dioxygen into a spin-paired state, or singlet oxygen. This intermediate is extremely reactive. The energy is supplied as heat. The reaction produces heat, which keeps it going. |
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| thyristor |
| Posted: Sat Jun 21, 2008 1:58 pm Post subject: |
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Forum Sophomore
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Posts: 190
Location: Sweden
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Ok, I read the article but since ENglish isn't my mothertongue didn't really get it all. Does singlet oxygen mean that all electrons are paired, if so why does this increase the probability for combustion so enormously?
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| Bunbury |
| Posted: Sun Jun 22, 2008 9:49 am Post subject: |
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Forum Ph.D.
Joined: 26 Sep 2007
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| You can follow the wiki links to read about singlet oxygen, but I can't help you any further than that. This goes beyond what we need for most industrial combustion engineering problems. |
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