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I'm balancing chemical equations, and I came across the following:
$$\ce{O2 + C4H9NH2 -> CO2 + H2O + N2}\tag{unbalanced}$$

My initial reaction was that it is a combustion reaction. According to my workbook, the definition is "an organic compound reacts with oxygen to form carbon dioxide and water." This equation seems to fit the bill. However, the solution states that in fact this is a decomposition reaction. In a YouTube video I saw, it said that decomposition reactions are a single reactant to multiple products. Where is the misunderstanding? Is it possible the workbook is wrong?

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    $\begingroup$ I would say your interpretation is more correct than the book's. $\endgroup$
    – Tyberius ♦
    Commented Dec 4, 2018 at 16:31
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    $\begingroup$ The workbook is wrong on some many levels. It is an oxidation, and you'd not get N2 but a nitrogen oxide of some sort depending on temperature and pressure. $\endgroup$
    – MaxW
    Commented Dec 4, 2018 at 17:32
  • $\begingroup$ @MaxW I think OP could benefit from you turning that into an actual answer ;) $\endgroup$
    – Jan
    Commented Dec 5, 2018 at 15:46

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You're right, I'd consider that a decomposition reaction is primarily a single chemical species breaking into other chemical species. Here is the IUPAC Gold Book definition for decomposition.

The IUPAC definition specifically mentions two phases, which implies that the decomposition is "irreversible." In other words, there isn't a significant backwards reaction.

The molecular formula $\ce{C4H9NH2}$ could be a number of different aliphatic primary amines, but all of them are stable under ordinary conditions. In other words, you'd have to "burn" them in a combustion reaction with oxygen to get $\ce{CO2}$ and $\ce{H2O}$. In such a reaction I would absolutely not expect to get $\ce{N2}$ as a product. Rather I'd expect some sort of nitrogen oxide $\ce{NO_x}$. Which one would depend on temperature, pressure, and the proportion of oxygen.

So the unbalanced reaction would better be written as: $$\ce{O2 + C4H9NH2 ->[\Delta] CO2 + H2O + NO}_x$$

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  • $\begingroup$ I disagree. When you burn simple organics, you get most of your nitrogen as N2. Maybe a few percent go to NOx. $\endgroup$
    – Ivan Neretin
    Commented Dec 5, 2018 at 18:15
  • $\begingroup$ @IvanNeretin - For both n-butyl amine and for tert-butylamine PubChem says "Produces toxic oxides of nitrogen during combustion." $\endgroup$
    – MaxW
    Commented Dec 5, 2018 at 18:31
  • $\begingroup$ Well, the mentioned few percent are quite enough of a reason to bother about toxicity. $\endgroup$
    – Ivan Neretin
    Commented Dec 5, 2018 at 18:34

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