THE OZONETOPIC 5.3

1 2

3 4

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

○ energy is breaking ozone “1.5” double bondsgood- UV energy is doing that instead of reaching Earth

resonates between these two structures

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 oxygenClO + 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