Chapter 6, Problem 107RQ

Chlorofluoromethanes (CFMs) are carbon compounds of chlorine and fluorine and are also known as Freons. Examples are Freon-11 ${\text{(CFCl}}_{\text{3}}\text{)}$ and Freon-12 $\left({\text{CF}}_{\text{2}}{\text{Cl}}_{\text{2}}\right)$, which were used as aerosol propellants. Freons have also been used in refrigeration and air-conditioning systems. In 1995 Mario Molina, F. Sherwood Rowland, and Paul Crutzen were awarded the Nobel Prize mainly for demonstrating how these and other CFMs contribute to the “ozone hole” that develops at the end of the Antarctic winter. In other pares of the world, reactions such as those shown below occur in the upper atmosphere where ozone protects the earths inhabitants from harmful ultraviolet radiation. In the stratosphere CFMs absorb high-energy radiation from the sun and split off chlorine atoms that hasten the decomposition of ozone, ${\text{O}}_{\text{3}}$. Possible reactions are

$\begin{array}{l}{\text{O}}_{\text{3}}\left(g\right)+\text{Cl}\left(g\right)\to {\text{O}}_{\text{2}}\left(g\right)+\text{ClO}\left(g\right)\Delta H°=-126\text{ kJ}\\ \text{ClO}\left(g\right)+\text{O}\left(g\right)\to \text{Cl}\left(g\right)+{\text{O}}_{\text{2}}\left(g\right)\Delta H°=-268\text{ kJ}\\ {\text{O}}_{\text{3}}\left(g\right)+\text{O}\left(g\right)\to 2{\text{O}}_{\text{2}}\left(g\right)\Delta H°=?\end{array}$

The O atoms in the second equation come from the breaking apart of ${\text{O}}_{\text{2}}$ molecules caused by ultraviolet radiation from the sun. Use the first two equations to calculate the value of $\Delta H°$

(in kilojoules) for the last equation, the net reaction for the removal of ${\text{O}}_{\text{3}}$ from the atmosphere.