Question

How does CFC and $N{{O}_{2}}$ deplete ozone layer? Explain it with a balanced chemical equation?

Answer 1

The use of CFC is reduced because of the fact that it destroys the ozone layers which protects the earth from ultraviolet radiations coming from the sun. The ozone layer breaks into oxygen molecules and free oxygen, and the CFCs along with $N{{O}_{2}}$ acts as a catalyst in this process.

Complete step-by-step answer:
The CFC and the $N{{O}_{2}}$ are responsible for the ozone layer depletion as both of them have the tendency to enable the atoms of oxygen to react with the ozone layer and tamper or destroy it.
We know that the sunlight has the tendency to react with the oxygen gas in order to break the molecule into its constituent oxygen atoms. It can be expressed in a chemical equation as,
${{O}_{2}}\xrightarrow{h\nu }{{O}^{.}}{{+}^{.}}O$

This reaction can be catalysed by the Chloro fluoro carbons and the $N{{O}_{2}}$ present in the atmosphere, which results in faster destruction of the ozone layer. The CFCs catalyse the ozone depletion by following a free radical mechanism and we will consider all the reactions which eventually leads to the depletion of the ozone layer.

At first the bond between carbon and chlorine break in order to form a chlorine atom, it would be termed as the chain initiation step. CFC will break, giving rise to a chlorine radical, the reaction is as follows,
$Cl-CFC{{l}_{2}}\xrightarrow{h\nu }Cl\cdot +\cdot CFC{{l}_{2}}$

In the next step which is also called the propagation step, the atom of the chlorine would undergo reaction with the molecule of ozone, which breaks the ozone. The reaction is as follows,
$Cl\cdot +{{O}_{3}}\to ClO+{{O}_{2}}$
This reaction gives rise to the formation of chlorine monoxide molecules along with the molecule of oxygen. Then one of the free oxygen atoms undergoes a reaction with the chlorine monoxide in order to form oxygen molecules and chlorine radicals.
$ClO+O\cdot \to Cl\cdot +{{O}_{2}}$

Now after addition of both the equation of chain propagation we will get,
$O\cdot +{{O}_{3}}\to 2{{O}_{2}}$

In a similar way, $N{{O}_{2}}$ also acts as a catalyst in destruction of the ozone layer, except this time the free radical would be $NO\centerdot$. And the rest of the procedure is the same. In the propagation step it will form nitrogen monoxide instead of chlorine monoxide.

The reactions are as follows,
$N{{O}_{2}}\xrightarrow{h\nu }\cdot NO+O\cdot$
Above is the reaction showing initiation of the process, where free radicals of nitrogen monoxide is formed. The next step would show the process of propagation.
$\cdot NO+{{O}_{3}}\to N{{O}_{2}}+{{O}_{2}}$

As we can see the molecule of nitrogen monoxide reacts with a molecule of the ozone layer and destroys it forming nitrogen dioxide and oxygen molecules.
$N{{O}_{2}}+O\cdot \to \cdot NO+{{O}_{2}}$

In the next step, the nitrogen dioxide molecule reacts with free oxygen and converts it to oxygen gas. Now if we combine both the equations of propagation, ultimately we will get.
$O\cdot +{{O}_{3}}\to 2{{O}_{2}}$

Hence, the CFCs and $N{{O}_{2}}$ are responsible for the depletion of the ozone layer.

Note: The ozone layer depletion catalysed by the CFCs and nitrogen dioxide, follows the free radical mechanism, where in both the cases free radical is formed which is returned as a product after the reaction, hence acting as a catalyst. In case of CFCs the free radical is formed in the chlorine, whereas in case of nitrogen dioxide the free radical is nitrogen monoxide.