Editing Ammonia (section)

=== Combustion ===
[[File:86. Каталитичка оксидација на амонијак.ogg|thumb|right|Heated [[Chromium(III) oxide|Cr<sub>2</sub>O<sub>3</sub>]] catalyzes the combustion of a flask of ammonia.]]
Ammonia does not burn readily or sustain [[combustion]], except under narrow fuel-to-air mixtures of 15–28% ammonia by volume in air.<ref>{{cite web |title=Ammonia |url=https://pubchem.ncbi.nlm.nih.gov/source/hsdb/162#section=Flammable-Limits |website=PubChem}}</ref> When mixed with [[oxygen]], it burns with a pale yellowish-green flame. Ignition occurs when [[chlorine]] is passed into ammonia, forming nitrogen and [[hydrogen chloride]]; if chlorine is present in excess, then the highly explosive [[nitrogen trichloride]] ({{chem2|NCl3}}) is also formed.

The [[combustion]] of ammonia to form nitrogen and water is [[exothermic]]:
{{block indent|1= {{chem2|4 NH3 + 3 O2 → 2 N2 + 6 H2O(g)}}, [[Standard enthalpy of reaction|Δ''H''°<sub>r</sub>]] = −1267.20&nbsp;kJ (or −316.8&nbsp;kJ/mol if expressed per mol of {{chem2|NH3}})}}

The [[standard enthalpy change of combustion]], Δ''H''°<sub>c</sub>, expressed per [[mole (unit)|mole]] of ammonia and with condensation of the water formed, is −382.81&nbsp;kJ/mol. Dinitrogen is the thermodynamic product of [[combustion]]: all [[nitrogen oxide]]s are unstable with respect to {{chem2|N2}} and {{chem2|O2}}, which is the principle behind the [[catalytic converter]]. Nitrogen oxides can be formed as [[chemical kinetics|kinetic products]] in the presence of appropriate [[catalysts]], a reaction of great industrial importance in the production of [[nitric acid]]:
{{block indent| {{chem2|4 NH3 + 5 O2 → 4 NO + 6 H2O}}}}

A subsequent reaction leads to {{chem2|NO2}}:
{{block indent| {{chem2|2 NO + O2 → 2 NO2}}}}

The combustion of ammonia in air is very difficult in the absence of a [[catalyst]] (such as [[platinum]] gauze or warm [[chromium(III) oxide]]), due to the relatively low [[heat of combustion]], a lower laminar burning velocity, high [[auto-ignition temperature]], high [[heat of vaporization|heat of vapourization]], and a narrow [[Flammability limit|flammability range]]. However, recent studies have shown that efficient and stable combustion of ammonia can be achieved using swirl combustors, thereby rekindling research interest in ammonia as a fuel for thermal power production.<ref name="Kobayashi-2019">{{cite journal |last1=Kobayashi |first1=Hideaki |last2=Hayakawa |first2=Akihiro |last3=Somarathne |first3=K.D. Kunkuma A. |last4=Okafor |first4=Ekenechukwu C. |title=Science and technology of ammonia combustion |journal=Proceedings of the Combustion Institute |date=2019 |volume=37 |issue=1 |pages=109–133 |doi=10.1016/j.proci.2018.09.029 |doi-access=free |bibcode=2019PComI..37..109K }}</ref> The flammable range of ammonia in dry air is 15.15–27.35% and in 100% relative humidity air is 15.95–26.55%.<ref>{{cite book |last1=Khan |first1=A.S. |last2=Kelley |first2=R.D. |last3=Chapman |first3=K.S. |last4=Fenton |first4=D.L. |title=Flammability limits of ammonia–air mixtures |date=1995 |publisher=U.S. DOE Office of Scientific and Technical Information |location=U.S. |osti=215703 }}</ref>{{clarify|By mass, volume or mole fraction???|date=December 2022}} For studying the [[chemical kinetics|kinetics]] of ammonia combustion, knowledge of a detailed reliable reaction mechanism is required, but this has been challenging to obtain.<ref>{{Cite journal|last1=Shrestha|first1=Krishna P.|last2=Seidel|first2=Lars |last3=Zeuch|first3=Thomas |last4=Mauss|first4=Fabian |date=2018-07-07|title=Detailed kinetic mechanism for the oxidation of ammonia including the formation and reduction of nitrogen oxides|journal=Energy & Fuels|volume=32|issue=10|pages=10202–10217 |doi=10.1021/acs.energyfuels.8b01056|s2cid=103854263|issn=0887-0624 |url=https://hal.archives-ouvertes.fr/hal-02629067/file/Shrestha_Ammonia_NOx_2018.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://hal.archives-ouvertes.fr/hal-02629067/file/Shrestha_Ammonia_NOx_2018.pdf |archive-date=2022-10-09 |url-status=live}}</ref>