Environmental Chemistry - Result Question 24
####2. The correct set of species responsible for the photochemical smog is
(2019 Main, 12 April I)
(a) $N _2, NO _2$ and hydrocarbons
(b) $CO _2, NO _2, SO _2$ and hydrocarbons
(c) $NO, NO _2, O _3$ and hydrocarbons
(d) $N _2, O _2, O _3$ and hydrocarbons
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Answer:
Correct Answer: 2. (c)
Solution:
- The correct set of species responsible for the photochemical smog is $NO, NO _2, O _3$ and hydrocarbons. Photochemical smog appears in warm, dry and sunny climate which are obtained by the action of sunlight on unsaturated hydrocarbons and nitrogen oxides. Following reactions are involved during the formation of photochemical smog.
(i) $N _2(g)+O _2(g) \longrightarrow 2 NO(g)$
(Originates from
burning of fossil fuels)
(ii) $2 NO(g)+O _2(g) \xrightarrow{\text { Sunlight }} 2 NO _2(g)$
$$ NO _2(g) \stackrel{h v}{\longrightarrow} NO(g)+[O] $$
(iii) $O(g)+O _2(g) \rightleftharpoons O _3(g)$
$$ \text { Reacts rapidly with NO } $$
$$ \begin{aligned} & O _3(g)+NO(g) \longrightarrow \underset{\begin{array}{c} \text { Brown gas (in high } \ \text { concentration form haze) } \end{array}}{NO _2(g)+O _2(g)} \ & \underset{\text { (Unburnt hydrocarbon) }}{3 CH _4(g)}+2 O _3(g) \longrightarrow \underset{\text { Formaldehyde }}{3 CH _2=O(g)} \ &+CH _2=\underset{\text { Acrolein }}{CHCH}=O+H _2 O \end{aligned} $$
