1. Section 2.8—Speeding Up A Reaction
How can we make those antacid reactions occur faster?

2. Kinetics & Reaction Rates
Kinetics – Study of the rates of reactions
Reaction Rate – Rate at which reactants produce products

3. Collision Theory
Collision Theory – Defines 3 circumstances to be met for a reaction to occur. 1
Reactants must collide 2
Collision must be at the correct orientation
Collision must have minimum energy for reaction to occur 3
Only a small number of collisions meet the requirements and result in a reaction

4. Collisions Must Occur
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!

5. Collision with Correct 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.

6. 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 F
But not every collision produces a reaction—they must collide in the correct orientation to react
This is the correct orientation. The reaction will happen.

7. Collision with 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

8. 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..

9. Activation Energy
Minimum energy for reaction to occur during a collision

10. Reaction Coordinate Diagram
Reaction coordinate diagrams show the energy changes throughout the reaction
Activated complex
(Also called the transition state)
Activation Energy
Products
Energy
Energy change for reaction
Reactants
Reaction proceeds

11. Activated Complex What is an “activated complex”? F N O N O F F
Reaction proceeds
Energy
Activated Complex
Reactants
F2NO2
F2 + NO2
Products
F + FNO2 F N O N O F F

12. Factors Affecting Reaction Rates

13. Surface Area of Reactants
How does the surface area of the reactants affect the reaction rate?
More reactants can collide at the same time and a fraction of those will result in 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

14. Concentrations of Reactants
How does the concentration of reactants affect the reaction rate?
Only a small fraction of the collisions meet the requirements and result in a reaction
If more collisions occur, more will meet the requirements and result in a reaction
More reactants mean more collisions will occur
As reaction concentration increases, reaction rate increases

15. 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
If molecules are at a higher temperature, they have a higher average kinetic energy
Reactants must collide with at least energy equal to the activation energy
For most reactions, as temperature increases, reaction rate increases

16. Catalysts
Catalysts – Substance that increases the rate of reaction without being used up
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

17. Catalysts
How do catalysts help speed up the reaction without being used?
They increase the chances that a collision will successfully produce a reaction
For example, catalysts hold one or more of the reactants in place to allow collisions to occur with the correct orientation
Catalysts make a successful collision more likely. They lower the activation energy by allowing reactants to react in a different way, or by holding reactants in place for the reaction. Once they’ve done their job, they are released and available to “help” another reactant.
Once the reaction has occurred, the catalyst releases the molecule(s) and finds another one to help

18. Catalysts & Reaction Diagrams
Reaction Path without catalyst
Reaction Path with catalyst
Energy
Reaction proceeds
Catalysts lower the activation energy of the reaction by letting it proceed in a different way.
With lower activation energy, a higher percentage of collisions will be successful (they don’t need to collide with as much energy to be successful)