question_answer 41)

  On the basis of chemical reactions involved, explain how do chlorofluorocarbons cause thinning of ozone layer in stratosphere?

Answer:

  Chlorofluorocarbons are introduced into the atmosphere from aerosol sprays in which they function as propellants and from refrigerating equipments in which they act as coolants. They are also used as solvents. They have very long life and stay in atmosphere for years and ultimately reach the upper layer (stratosphere) where they decompose in presence of UV-radiations of the sun. On account of decomposition, chlorine atoms or free radicals.                                 \[C{{F}_{2}}C{{l}_{2}}\xrightarrow{hv}{{\,}^{\centerdot }}C{{F}_{2}}Cl+C{{l}^{\centerdot }}\] The active chlorine atoms then destroy the ozone layer. \[C{{l}^{\centerdot }}+{{O}_{3}}\to Cl{{O}^{\centerdot }}+{{O}_{2}}\] \[Cl{{O}^{\centerdot }}+O\to C{{l}^{\centerdot }}+{{O}_{2}}\] It has been found that one molecule of chlorofluorocarbon can destroy one thousand \[{{O}_{3}}\] molecules in the stratosphere.