From what I've seen in alkanes, their complete combustion creates carbon dioxide, which has carbon in its highest possible oxidation state. I've been wondering what complete combustion would look like in similar compounds, such as ammonia, phosphine, hydrogen sulfide, and silane.

After looking at through several search results of The combustion of <compound> and <compound>'s reaction with oxygen, I was surprised to only see that the search results for silane and phosphine generally showed that the combustion products attained their maximum oxidation state.

For example, the general result for ammonia seems to be nitrogen monoxide or nitrogen dioxide, which make sense as products for incomplete combustion, but I would think that a complete combustion would produce dinitrogen pentoxide. Hydrogen sulfide's combustion also seems to form sulfur dioxide or disulfur dioxide rather than sulfur trioxide.

This really confused me, since I was expecting the main products of all these reactions to be fully oxidized nonmetallic oxides. My question is, how can one predict what the fully combusted products of an inorganic, hydrogen containing compound look like?

Links for my ammonia query:

http://www.questionsolutions.com/ammonia-gas-reacts-molecular-oxygen-gas/ https://answers.yahoo.com/question/index?qid=20150615223643AArPdtu https://answers.yahoo.com/question/index?qid=20080504104957AAgQrL3

Links for my hydrogen sulfide query:




1 Answer 1


The "completeness" of combustion depends on the proportion of the reactants, and on the temperature cycle, not only the peak temperature, but the rate at which the products are quenched. For example, using ammonia and air as fuel in internal combustion engines produces mostly $\ce{H2O}$ and $\ce{N2}$, with less than 0.1% $\ce{NO_x}$ according to Kobayashi, et. al. and Zacharakis-Jutz.

The greatest oxidation state of a substance is often not thermodynamically stable. Perchlorates, chlorine dioxide , $\ce{H2O2}$ and similar compounds are somewhat unstable (i.e., BANG) and are not generally released in great quantities by combustion.


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