1. Unit 8: Rates of Reactions
Collision Theory

2. Collision Theory
In order for a reaction to occur…
Reactants must collide 1 2
Collision must be at the correct orientation 3
Collision must have minimum amount of energy for bonds to break
Only a small number of collisions meet the requirements and result in a reaction

3. 1. Reactants Must Collide
In order for two molecules to react, they must come in contact with one another N O F
There’s no way they’ll ever react if they don’t run into one another!

4. 2. Collision with Incorrect Orientation
For a collision to result in a chemical reaction, it must occur with the correct orientation N O F
This is not the correct orientation. The reaction will not happen.

5. 2. Collision with Correct Orientation
For a collision to result in a chemical reaction, it must occur with the correct orientation F N O N O
But not every collision produces a reaction—they must collide in the correct orientation to react F F
This is the correct orientation. The reaction will happen.

6. 3. Collision with Not Enough Energy
For a collision to result in a chemical reaction, it must occur with the minimum energy for reaction
Temperature:
10 oC N O F
The collision does not have enough energy to produce a reaction

7. 3. Collision with Enough Energy
For a collision to result in a chemical reaction, it must occur with the minimum energy for reaction
Temperature:
28 oC F N O N O F F
This collision had more energy (faster moving molecules). A reaction will occur..

8. Factors Affecting Reaction Rate
Temperature
Concentration
Surface Area
Catalysts

9. For most reactions, as temperature increases, reaction rate increases
Higher Temperature = faster molecules
Faster molecules:
More likely to collide
Higher energy when they collide
Reaction more likely to happen
For most reactions, as temperature increases, reaction rate increases

10. Concentrations of Reactants
More reactants = more likely to collide
Reaction more likely to happen
For most reactions, as reactant concentration increases, reaction rate increases

11. Surface Area of Reactants
Higher surface area = reactants more likely to collide
Reaction more likely to happen
As surface area increases, reaction rate increases

12. Catalysts
Catalyst: – a substance that increases the rate of reaction without being used up
creates a lower energy reaction pathway
Example: enzymes in the body