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Explain the formation of photochemical smog with reactions. |
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Answer» Solution :When fossil fuels are burnt, a variety of pollutants are emitted into the earth.s troposphere. Two of the hydrocarbons and NITRIC oxide build up sufficiently HIGH level. A chain reaction occurs from their interaction with sunlight in which NO is converted into nitrogen dioxide `(NO_2)`. This `NO_2` in turn absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom.  Oxygen atoms are very reactive and combine with the `O_2` in air to produce ozone. `O_((g)) + O_(2(g)) hArr O_(3(g))"".........(ii)` The ozone formed in the above reaction (ii) reacts rapidly with the `NO_((g))` formed in the reaction (i) to regenerate `NO_2. NO_2` is a brown gas and at sufficiently high levels can contribute to haze. `NO_((g)) + O_(3(g)) to NO_(2(g)) +O_(2(g)) ......... (iii)` Ozone is a toxic gas and both `NO_2` and `O_3` are strong OXIDISING agents and can react with the unburnt hydrocarbons in the polluted air to produce chemicals such as formaldehyde, acrolein and PEROXYACETYL nitrate (PAN). `3CH_4 + 2O_3 to underset("Formaldehdye")(3CH_2 =O) + 3H_2 O` `CH_2 = underset("Acroline")(CHCH)=O "" underset("Peroxyacetyl nitrate (PAN)")(CH_3underset(O)underset(||)C OO NO_2)` |
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