Question

Describe the chemical reaction occurring in the atmosphere.

Answer 1

Atmosphere consists of a layer of gases that includes nitrogen, oxygen, carbon dioxide, argon, and many other small amounts of gases. It is composed of $78$ nitrogen, $21$ oxygen, $0.93$ argon and $0.04$ carbon dioxide.

Complete step by step answer:
Atmosphere is divided into four layers.
Let us see the four different layers of atmosphere.
1.Troposphere: In the troposphere, all the biological activities take place. It is the lowest layer lying just above the surface of the Earth. The reaction that takes place in the troposphere includes carbon dioxide and water vapors. When sunlight passes the troposphere, the carbon dioxide molecule absorbs large amounts of energy in this region and excitation takes place.
$C{{O}_{2}}\xrightarrow{h\nu }C{{O}_{2}}'$
The excited molecule of $C{{O}_{2}}'$ collides with other molecules. These molecules contain excess energies that are converted into heat and temperature that raise the atmosphere. Water vapors also show the similar behavior in this region.

2.Stratosphere: In the stratosphere, formation and dissociation of ozone takes place. This reaction occurs in two steps.
The reactions of formation of ozone can be written as follows:
i.The UV radiations from the sun splits the dioxygen $({{O}_{2}})$ into two oxygen atoms.
${{O}_{2}}\xrightarrow{h\nu }O+O$
ii.Atoms then again react with dioxygen and result in the formation of ozone.
$O+{{O}_{2}}\to {{O}_{3}}$
The dissociation of ozone can be written as follows:
On absorbing UV radiation, ozone dissociates into dioxygen and oxygen atoms. Heat is released during this reaction that warms up the stratosphere.
In the stratosphere, photochemical decomposition of frayons takes place that results in the formation of chlorine atoms. Let us see the reactions.
$C{{F}_{2}}C{{l}_{2}}\xrightarrow{h\nu }C{{F}_{2}}Cl+Cl$
$CFC{{l}_{3}}\xrightarrow{h\nu }CFC{{l}_{2}}+Cl$
The ozone is destroyed due to these reactive chlorine atoms and result in the formation of chlorine oxide and dioxygen. The chlorine oxide then reacts with oxygen atom to give chlorine atom and dioxygen.
$Cl+{{O}_{3}}\to ClO+{{O}_{2}}$
$ClO+O\to Cl+{{O}_{2}}$

3.Mesosphere and thermosphere: Due to some photochemical reactions, electrons and free ions are released.
In the upper atmosphere, these free ions do not react with other species.
$NO\xrightarrow{h\nu }N{{O}^{+}}+{{e}^{-}}$
${{O}_{2}}\xrightarrow{h\nu }O_{2}^{+}+{{e}^{-}}$
$He\xrightarrow{h\nu }H{{e}^{+}}+{{e}^{-}}$
${{O}_{2}}\xrightarrow{h\nu }O+O$

Note: Carbon dioxide is formed in the troposphere, formation of ozone takes place in the stratosphere, chlorofluorocarbons are also formed in this layer along with other reactions of chlorine. In the mesosphere and thermosphere reaction of ions like nitrogen oxide, helium, oxygen takes place.