1. Chapter 17: Reaction Rates
Table of Contents
Chapter 17: Reaction Rates
17.1: Reaction Rates
ELEPHANT TOOTHPASTE – increase concentration and surface area

2. 1. Particles must collide in order to react.
Reaction Rates: Basic Concepts
Collision theory: atoms, ions, and molecules must collide with each other in order to react.
1. Particles must collide in order to react.
2. The particles must collide with the correct
orientation.
3. The particles must collide with enough energy to react.

3. Reaction Rates: Basic Concepts
Collision Theory
Activated complex or transition state: intermediate particle of joined reacts at collision.

4. It’s like there’s a “hump” or “barrier” between reactants and products
Reaction Rates: Basic Concepts
Collision Theory
It’s like there’s a “hump” or “barrier” between reactants and products
Activation energy (Ea): the minimum amount of energy needed for reactants to reorganize and become products

5. Effects of Activation energy (Ea):
Reaction Rates: Basic Concepts
Collision Theory
Effects of Activation energy (Ea):
high Ea
few collisions will have the energy required to produce an activated complex
reaction rate will be low (slow).
low Ea
many collisions will have the energy required to produce an activated complex
reaction rate will be high (fast).

6. Reaction Rates: Basic Concepts
Collision Theory
EXOTHERMIC

7. Reaction Rates: Basic Concepts
Collision Theory
ENDOTHERMIC

8. Chapter 17: Reaction Rates
Table of Contents
Chapter 17: Reaction Rates
17.2: Factors Affecting Reaction Rates

9. Factors Affecting Reaction Rates
Reaction Rates: Basic Concepts
Factors Affecting Reaction Rates
Reaction Rate: The speed at which a reaction progresses
can be changed depending on conditions

10. 1. The Nature of Reactants
Reaction Rates: Basic Concepts
1. The Nature of Reactants
The more reactive a substance is, the faster the reaction rate.
“Reactive” means that a substance has the tendency to react.

11. More particles means more collisions
Reaction Rates: Basic Concepts
2. Concentration
Increasing concentrations of reacting particles increases reaction rate.
More particles means more collisions

12. Reaction Rates: Basic Concepts
3. Surface Area
Increasing the surface area of reactants provides more opportunity for collisions with other reactants, thereby increasing the reaction rate.

13. Reaction Rates: Basic Concepts
4. Temperature
Increasing the temperature at which a reaction occurs increases the reaction rate.
Particles move faster and have more energy to create activated complexes

14. Catalysts create a new pathway with lower activation energy

15. 5. Catalysts
Catalyst: a substance that increases the rate of a chemical reaction without itself being consumed in the reaction.
CATALYZED
activation energy lower
more collisions have sufficient energy to initiate reaction
UNCATALYZED
activation energy higher
fewer collisions have sufficient energy to initiate reaction

16. Heterogeneous and homogeneous catalysts
Reaction Rates: Basic Concepts
Heterogeneous and homogeneous catalysts
A heterogeneous catalyst is in a different physical state the reaction it catalyzes.
Example: Reactants = solids
heterogeneous catalyst = gas

17. Heterogeneous and homogeneous catalysts
Reaction Rates: Basic Concepts
Heterogeneous and homogeneous catalysts
A homogeneous catalyst is in the same physical state as the reaction it catalyzes
Example: Reactants = aqueous
homogeneous catalyst = aqueous

18. Enzymes: Biological catalysts
Reaction Rates: Basic Concepts
5. Catalysts
Enzymes: Biological catalysts
An inhibitor is a substance that slows down, or inhibits, reaction rates.