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Thread: Combustion

  1. #1 Combustion 
    Forum Masters Degree thyristor's Avatar
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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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    Forum Isotope Bunbury's Avatar
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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.

    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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    Forum Masters Degree thyristor's Avatar
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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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  5. #4  
    Forum Isotope Bunbury's Avatar
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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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