Question

How does CFC and NO2 deplete ozone layer? Explain it wih balanced chemical equation?

Answer 1

Warning! Long Answer. Here's what I get.

Explanation:

CFCs and `"NO"_2` enable oxygen atoms to react with ozone and destroy it.

Sunlight reacts with oxygen an breaks it into oxygen atoms.

`bb((1.))color(white)(m)"O"_2 stackrelcolor(blue)(hnucolor(white)(mm))(→) "O·" + "·O"`

CFCs and `"NO"_2` provide the catalysts that enable oxygen atoms to react quickly with ozone with ozone and destroy it.

CFCs and ozone depletion

The process is a free radical chain reaction.

In the initiation step (2), a photon of ultraviolet light hits a CFC molecule, say, `"CFCl"_3`.

A `"C-Cl"` bond breaks, forming a `"Cl"` atom.

`bb((2.))color(white)(m)"Cl-CFCl"_2 stackrelcolor(blue)(hnucolor(white)(mm))(→) "Cl·" + "·CFCl"_2`

In the propagation steps (3 and 4), the chlorine atom reacts with an ozone molecule, breaking it apart and destroying the ozone.

`bb((3.))color(white)(m)"Cl·" + "O"_3 → "ClO" + "O"_2`

The reaction forms a chlorine monoxide molecule and an oxygen molecule.

Then a free oxygen atom reacts with the chlorine monoxide to form oxygen and a chlorine atom.

`bb((4.))color(white)(m)"ClO" + "O·" → "Cl·" + "O"_2`

The chlorine atom is free to repeat the process of destroying more ozone molecules.

A single CFC molecule can destroy 100 000 ozone molecules.

If we add Equations 3 and 4, we get the overall equation 5 for the reaction.

`bb((3.))color(white)(m)color(red)(cancel(color(black)("Cl·"))) + "O"_3 → color(red)(cancel(color(black)("ClO"))) + "O"_2`
`bb((4.))color(white)(m)ul(color(red)(cancel(color(black)("ClO"))) + "O·" → color(red)(cancel(color(black)("Cl·"))) + "O"_2)`
`bb((5.))color(white)(mm)"O·" + "O"_3 → 2"O"_2`

`"NO"_2` and ozone depletion

The process is a free radical chain reaction.

In the initiation step (6), a photon of ultraviolet light hits an `"NO"_2` molecule, breaking an `"N-O"` bond and forming an `"·NO"` molecule and an `"O"` atom.

`bb((6.))color(white)(m)"NO"_2 stackrelcolor(blue)(hnucolor(white)(mm))(→) "·NO" + "O·"`

In the propagation steps (7 and 8), the nitrogen monoxide reacts with an ozone molecule, breaking it apart and destroying the ozone.

`bb((7.))color(white)(m)"·NO" + "O"_3 → "NO"_2 + "O"_2`

The reaction forms a nitrogen dioxide molecule and an oxygen molecule.

Then a free oxygen atom reacts with the nitrogen dioxide to form oxygen and nitrogen monoxide.

`bb((8.))color(white)(m)"NO"_2 + "O·" → "·NO" + "O"_2`

The nitrogen monoxide is free to repeat the process of destroying more ozone molecules.

The nitrogen monoxide is a catalyst because it reacts at the beginning and is regenerated at the end.

If we add Equations 7 and 8, we get the overall equation 9 for the reaction.

`bb((7.))color(white)(m)color(red)(cancel(color(black)("·NO"))) + "O"_3 → color(red)(cancel(color(black)("·NO"_2))) + "O"_2`
`bb((8.))color(white)(m)ul(color(red)(cancel(color(black)("·NO"_2))) + "O·" → color(red)(cancel(color(black)("·NO"))) + "O"_2)`
`bb((9.))color(white)(mmll)"O·" + "O"_3 → 2"O"_2`

Note that the overall reaction is the same whether a CFC or nitrogen dioxide is the culprit.