1. Ch. 16 – Reaction Energy and Reaction Kinetics
I. Rates of Reaction
Ch. 16 – Reaction Energy and Reaction Kinetics

2. A. Collision Theory
Reaction rate depends on the collisions between reacting particles
Successful collisions occur if the particles...
collide with each other
have the correct orientation
have enough kinetic energy to break bonds

3. Unsuccessful Collisions
A. Collision Theory
Particle Orientation
Required Orientation
Unsuccessful Collisions
Successful Collision

4. B. Activation Energy Activation Energy (Ea)
minimum energy required for a reaction to occur
Activated Complex: the transitional structure in a collision that exists while old bonds are breaking and new bonds are being formed
Activation
Energy

5. B. Activation Energy Activation Energy: - depends on reactants
- is always positive
- low Ea = fast reaction rate
- takes less energy for the reaction to start Ea

6. C. Factors Affecting Rxn Rate
1. Nature of Reactants
- the rate of reaction depends on the particular reactants and the bonds involved
2. Surface Area
high SA = fast rxn rate
more opportunities for collisions
Increase surface area by…
using smaller particles – increase locations of collisions
dissolving in water – particles can mix & collide freely so reactions happen rapidly

7. C. Factors Affecting Rxn Rate
3. Concentration
- high conc = fast rxn rate
- more opportunities for collisions because there are more particles in the same volume that can react
There are fewer red particles in the same volume so there is a lower chance of a collision
There are more red particles in the same volume so there is more chance of a collision so the reaction goes faster

8. C. Factors Affecting Rxn Rate
4. Temperature
- high temp = fast rxn rate
- high KE
- ↑ temperature, ↑ energy
- particles move faster
- more opportunities for collision
- easier to reach activation energy

9. C. Factors Affecting Rxn Rate
5. Catalyst
substance that increases rxn rate without being consumed in the rxn
lowers the activation energy

10. Ch. 16 – Reaction Energy and Reaction Kinetics
II. Energy Diagrams
Ch. 16 – Reaction Energy and Reaction Kinetics

11. A. Terms and Symbols Reactants: chemicals to start in a reaction
Products: chemicals formed during reaction
Heat of reaction (DHrxn): difference in energy between reactants and products (units are Joules)
Activation Energy (Ea): amount of energy required for the reaction to take place. The higher the Ea, the slower the reaction (units are Joules)

12. B. Energy Diagrams
Show relationship between time and energy during the course of a chemical reaction
- -
Reactants DH
Products
Forward Rxn
(exothermic)
Reverse Rxn
(endothermic) Ea
Course of Reaction (time)
Energy (E) in kJ/mol

13. C. Endothermic Reaction
Products have higher enthalpy than reactants
The pink curve is the uncatalyzed reaction
The blue curve shows what happens when a catalyst is present
Energies and amounts of the products and reactants stays the same, and the DHrxn stays the same – catalyst just allows reaction to reach equilibrium faster
Course of Reaction
Energy
A reaction in which heat is absorbed

14. D. Exothermic Reactions
Reactions in which heat is released
Products have lower enthalpy than reactants
The blue curve shows un-catalyzed reaction, red curve shows what happens when a catalyst is present
Only change is the amount of time for the reaction to reach equilibrium
Referred to as “spontaneous” because they can proceed to products without outside intervention
Course of Reaction
Energy