NO, a gas formed by the reaction of N2 with O2 in internal combustion engines

In internal combustion engines, such as those found in automobiles, nitrogen monoxide (NO) is often formed by the reaction of nitrogen gas (N₂) and oxygen gas (O₂) during the combustion process. The reaction is as follows:

N2​(g)+O2​(g)→2NO(g)

In this reaction, the high temperatures and pressures in the combustion chamber of the engine lead to the formation of nitrogen monoxide. Nitrogen monoxide is a reactive gas and can further react with oxygen to form nitrogen dioxide (NO₂):

2NO(g)+O2(g)→2NO2​(g)

Together, nitrogen monoxide (NO) and nitrogen dioxide (NO₂) are often referred to as NOₓ (pronounced "nox"), which represents a group of nitrogen oxides. These nitrogen oxides are components of automotive exhaust and contribute to air pollution. Efforts are made to control and reduce the emissions of nitrogen oxides from internal combustion engines to mitigate their environmental impact.