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3.  ozone (O 3 ) is both created and destroyed in the atmosphere  UV from the sun splits molecular oxygen (O 2 ) into single atoms (O) that then combine with O 2 to form ozone (O 3 )  ozone absorbs harmful radiation from the Sun

4.  UV will decompose O 3 easier than O 2 O 2 bond enthalpy = 498 kJ mol -1 ○ breaking O 2 is always breaking double bonds O 3 bond enthalpy = 364 kJ mol -1 ○ energy is breaking ozone “1.5” double bonds good- UV energy is doing that instead of reaching Earth resonates between these two structures

5. Chlorofluorocarbons (CFCs)  used as a refrigerant (Freon)  non-toxic and low level of reactivity  however, when exposed to UV in stratosphere… Cl · + O 3 → ClO + O 2 ○ the chlorine atom changes an ozone molecule to ordinary oxygen ClO + O 3 → Cl · + 2 O 2 ○ the ClO from the previous reaction destroys a second ozone molecule and recreates the original chlorine atom, which can repeat the first reaction and continue to destroy ozone