Talk:Combustion

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Archives

1. Inception - May 2007

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Factual error

This was a dispute over the inclusion of N2 in the equation of complete combustion since it doesn't react. It was decided it should be kept since it affects the temperature and does react to make minor species. Full details are in the Combustion Archive.

Improvements needed

This was a dispute that spawned from confusion over different terminology meaning the same thing, particular adiabatic combustion temperature with adiabatic flame temperature and heat of combustion with heating value. It was decided that a more conscious effort should be made to include multiple terminology but to also to point the terms are equivalent. Full details are in the Combustion Archive.

Away from the basics

Does anyone understand what characteristic of oxygen makes combustion happen? What is it about reactions with that specific element that makes fire? How does that attribute work which makes it different from any other reaction that is not combustion? I'd appreciate any input. Thank you.

Typo regarding Nitrogen

In the "Complete vs. incomplete" section:

"Nitrogen does not take part in combustion, but at high temperatures, some nitrogen will be converted to NOx, usually between 1% and 0.002% (2 ppm)."

One of those figures (0.002% and 2 ppm) has to be wrong, because...

0.002% would be 20 ppm.

0.0002% would be 2 ppm.

I would change it myself but I don't know which figure is the correct one, and having no luck searching online. — Preceding unsigned comment added by Mikecurse (talk • contribs) 18:29, 26 October 2010‎

yeah, i agree with this, i'd assume 0.002% is right, however, i will do more research before i seeks to correct it

Fringe theories

I removed the following paragraph, and it has been re-added:

Combustion of an organic fuel in air is always exothermic because the double bond in O₂ is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products CO₂ and H₂O results in the release of energy.^[1] The bond energies in the fuel play only a minor role, since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH₄ is nearly the same as that of CO₂. The heat of combustion is approximately −418 kJ per mole of O₂ used up in the combustion reaction, and can be estimated from the elemental composition of the fuel.^[1]

The sole reference is a self-cited paper (the author of the paper is the editor who added the paragraph).

That the claims are also incorrect isn't really relevant to this, but I'd just like to point out that no great chemical insight is required to determine that they are. Combustion, for example, is exothermic by definition (so there's no need to explain why it is in a special case), and there are organic molecules which, depending on your definition, do not combust or require no O₂ to do so.

IpseCustos (talk) 09:00, 10 June 2022 (UTC)[reply]

This short paragraph makes correct and relevant scientific statements about bond energies and the heat of combustion. It states documented, verifiable facts based on universally accepted values of bond energies. That heats of reaction, including combustion, can be estimated from bond energies is also universally accepted in chemistry. A peer-reviewed reference providing all the details is provided for verification. In short, nothing is scientifically incorrect about this paragraph.

The claim that "combustion ... is exothermic by definition" is highly questionable and needs to be referenced. Combustion of an organic fuel is an example of a chemical reaction, and the heat of reaction depends on the bond energies or on the enthalpies of formation of reactants and products. How does any heat of reaction become negative (exothermic) by definition?

Furthermore, an "analysis" just "by definition" is unable to provide good quantitative estimates of the heats of combustion, unlike the last sentence in the quoted paragraph. Why, for instance, is the heat of combustion, per gram, of carbohydrates more than twice smaller than that of fat? Because carbohydrates, containing oxygen atoms, react with less O₂ than the corresponding mass of fat. A mere definition does not provide this useful result.

The last sentence by IpseCustos also does not hold up to careful scrutiny. The quoted paragraph, being about "Combustion of an organic fuel in air", makes no statement about "organic molecules which ... do not combust". Next, if organic molecules "require no O2 to do so." then they violate the definition of combustion given in the first sentence of the Wikipedia article and possibly the premise of "Combustion of an organic fuel in air".

Editors are of course free to replace this paragraph with a better, even more widely applicable and more accurate explanation (properly sourced) of the heat of combustion and its quite strict proportionality with the amount of oxygen consumed. But just deleting this correct short paragraph with its explanation of a central quantitative aspect of the heat of combustion is not in the interest of Wikipedia readers.

Klaus Schmidt-Rohr (talk) 14:58, 10 June 2022 (UTC)[reply]

To the concerns in my edit summary, I'd add that the details of energetics may be unsuitable for that point in the article. XOR'easter (talk) 17:02, 15 June 2022 (UTC)[reply]

^ ^a ^b Schmidt-Rohr, K (2015). "Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O₂". J. Chem. Educ. 92 (12): 2094–2099. Bibcode:2015JChEd..92.2094S. doi:10.1021/acs.jchemed.5b00333.

[Schmidt-Rohr_15-1] Schmidt-Rohr, K (2015). "Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O₂". J. Chem. Educ. 92 (12): 2094–2099. Bibcode:2015JChEd..92.2094S. doi:10.1021/acs.jchemed.5b00333.

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