Chapter 17.1 How chemical
reactions occur.
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Molecules react by colliding.
2 BrNO  2 NO + Br2
1. Two BrNO molecules approach each
other at high speeds.
2. The collision occurs.
3. The energy of the collision causes Br-N
bonds to break and Br-Br bonds to form.
4. The products: one Br2 and two NO
molecules.
Collision Model
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Collision Model = Reactions occur during
molecular collisions. The reaction rate is
directly related to the number of collisions.
This model explains why a reaction
proceeds faster if the concentrations of the
reacting molecules are increased or the
temperature is increased.
17. 2 Activation energy
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Activation energy (Ea) = minimum energy
needed for a reaction to occur (at higher
temperatures, the average collions have
more energy)
17.2 Catalyst
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Catalyst = a substance that speeds up a
reaction without being consumed.
Enzymes are catalysts in your body.
They allow bodies to speed up complicated
reactions that would be too slow to sustain
life at normal body temperatures. Because
of the lower activation energy, more
collisions will have enough energy to allow
a reaction.
Ozone
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The breakdown of ozone (O3) is catalyzed
by chlorine atoms.
One chlorine atom can catalyze the
destruction of about 1 million ozone
molecules per second.
Cl + O3  ClO + O2
O + ClO  Cl + O2