Question

Air contain 99% $N_{2}$ and $O_{2}$ gases. Then why don't they combine to form NO under the standard conditions? Given that the standard free energy of formation of NO(g) is 86.7 kJ $mol^{-1}$.

Answer 1

Air contains 99% of Nitrogen and Oxygen. Given, the standard free energy of formation of NO is 86.7 $\quad KJ{ mol }^{ -1 }$. These gases at sea level "do not react" with each other and form Nitric acid. But they "combine" to form the nitric oxide (NO) at temperature above $1210^{°}C$. It is then oxidized by the ozone to Nitrogen dioxide. Nitrogen dioxide is toxic to living tissues, and produce acid rain and photochemical smog.

Answer 2

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