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ozone (O3) is both created and destroyed in
the atmosphere
 UV from the sun splits molecular oxygen (O2)
into single atoms (O) that then combine with O2
to form ozone (O3)
 ozone absorbs harmful radiation from the Sun


UV will decompose O3 easier than O2
 O2 bond enthalpy = 498 kJ mol-1
○ breaking O2 is always breaking double bonds
 O3 bond enthalpy = 364 kJ mol-1
resonates between these two structures
○ energy is breaking ozone “1.5” double bonds
 good- UV energy is doing that instead of reaching Earth
Chlorofluorocarbons (CFCs)
used as a refrigerant (Freon)
 non-toxic and low level of reactivity
 however, when exposed to UV in stratosphere…

 Cl· + O3 → ClO + O2
○ the chlorine atom changes an ozone molecule to
ordinary oxygen
 ClO + O3 → Cl· + 2 O2
○ 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