1. Unit 4: Kinetics
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 F
But not every collision produces a reaction—they must collide in the correct orientation to react 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 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 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. Concentrations of Reactants
How does the concentration of reactants affect the reaction rate?
If more collisions occur, more will meet the requirements and result in a reaction
Only a small fraction of the collisions meet the requirements and result in a reaction
More reactants mean more collisions will occur
For most reactions, as reactant concentration increases, reaction rate increases

10. Surface Area of Reactants
How does the surface area of the reactants affect the reaction rate?
If more collisions occur, more will meet the requirements and result in a reaction
Larger surface area means more particles can come in contact with each other at the same time
Reactants must collide in order to react
As surface area increases, reaction rate increases

11. For most reactions, as temperature increases, reaction rate increases
How does temperature affect the reaction rate?
With higher energy molecules, collisions will have higher energy and more often result in reaction
Reactants must collide with at least energy equal to the activation energy
If molecules are at a higher temperature, they have a higher average kinetic energy
For most reactions, as temperature 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
A + B + C  D + C
“C” is the catalyst…it is present in the beginning and in the end
Enzymes are catalysts in the body