CHEM 120B Lecture Notes - Lecture 5: Ozone Layer, Activation Energy, Chlorine

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Catalysis
The Ozone Layer
The Ozone layer protects the earth from ultraviolet light, which is
harmful to living organisms.
The hole in the ozone layer was caused by humans.
Catalysts
When the ozone layer (oxygen atoms) were created, oxygen atoms
reacted with O3 rather than O2.
o This forms two O2 molecules.
o The activation energy is very high so the reaction occurs slowly.
o The release of chlorofluorocarbons in the air:
Ozone molecule (O3) slam into ClO atom.
Then ClO and oxygen atom make chlorine and oxygen gas.
This is contrasted from the two oxygen molecules
formed without chlorofluorocarbons.
Catalyst: undergoes no net change in concentration.
o Chlorine is the catalyst.
This process has a smaller activation energy; the reaction
then is faster.
The beginning and the end (delta-H) are the same
but the different pathway/mechanism lowers the
activation energy.
Catalysts: stay constant in their concentration.
o Similar to intermediates in that they do not appear in the net
chemical equation.
o However, intermediates always have a small concentration (they
are made only to be quickly used up).
Examples: Enzyme Catalysis
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