How are nitrogen oxides formed?

How are nitrogen oxides formed?

• A. Emitted by vehicles at low temperature
• B. Formed naturally during the combustion of wood, coal, and other fuels
• C. Produced by chemical interactions between atmospheric nitrogen and oxygen at high temperatures
• D. Formed only in outer space

Answer: (C)

Nitrogen oxides form when nitrogen in the air reacts with oxygen at high temperatures. The intense heat in combustion breaks the strong N≡N bond, allowing nitrogen atoms to combine with oxygen to make nitric oxide, which then becomes nitrogen dioxide in the presence of more oxygen. This thermal NOx mechanism is why engines, kilns, and power plants emit NOx. The other ideas don’t fit because the reaction requires high temperature and a plentiful supply of atmospheric N2 and O2; low temperatures don’t drive it, outer space lacks the atmospheric gases for this chemistry, and while burning fuels can contribute NOx in other ways, the primary formation route described here is the high-temperature reaction of N2 with O2.

Nitrogen oxides form when nitrogen in the air reacts with oxygen at high temperatures. The intense heat in combustion breaks the strong N≡N bond, allowing nitrogen atoms to combine with oxygen to make nitric oxide, which then becomes nitrogen dioxide in the presence of more oxygen. This thermal NOx mechanism is why engines, kilns, and power plants emit NOx. The other ideas don’t fit because the reaction requires high temperature and a plentiful supply of atmospheric N2 and O2; low temperatures don’t drive it, outer space lacks the atmospheric gases for this chemistry, and while burning fuels can contribute NOx in other ways, the primary formation route described here is the high-temperature reaction of N2 with O2.