Question

The reaction that is not involved in the ozone layer depletion mechanism is the stratosphere is:

• A. $HOCl\left(g\right)\stackrel{h\nu }{\to }\dot{O}H\left(g\right)+\dot{C}l\left(g\right)$
• B. $C{F}_{2}C{l}_2\left(g\right)\stackrel{UV}{\to }\dot{C}l\left(g\right)+\dot{C}{F}_{2}Cl\left(g\right)$
• C. $C{H}_4+2O_3\to 3C{H}_2=O+3H_{2}O$
• D. $Cl\dot{O}\left(g\right)+O\left(g\right)\to \dot{C}l\left(g\right)+O_2\left(g\right)$

Answer 1

Answer: (C)

$C{H}_4+2O_3\to 3C{H}_2=O+3H_{2}O$

(1) The upper stratosphere consists of a considerable amount of ozone which protects us from the harmful UV radiation coming from the sun. The main reason for depletion is CFCs.

(2) When released in the atmosphere, CFCs mix with the normal atmospheric gases and eventually reach the stratosphere. In the stratosphere, they get broken down by powerful UV radiations, releasing chlorine free radical.

$C{F}_{2}C{l}_2\left(g\right)\stackrel{hv}{\to }\dot{C}l\left(g\right)+\dot{C}{F}_{2}Cl\left(g\right)$

(3) The chlorine free radical $\left(\dot{C}l\right)$ then reacts with stratospheric ozone to form chlorine monoxide redicals $\left(Cl\dot{O}\right)$ and molecular $O_2$.

$Cl+O_3\left(g\right)\to Cl\dot{O}\left(g\right)+O_2\left(g\right)$

Reaction of $Cl\dot{O}$ with atomic oxygen produces more $\dot{C}l$ radicals.

$Cl\dot{O}+O\left(g\right)\to \dot{C}l\left(g\right)+O_2\left(g\right)$

So, the reaction of methane with ozone doesn't happen.

Option C is correct.