1. IV. Reaction Energy and Rates
Chemical Reactions
IV. Reaction Energy and Rates

2. A. Reaction Pathway
Shows the change in energy during a chemical reaction

3. 2H2(l) + O2(l)  2H2O(g) + energy
B. Exothermic Reaction
reaction that releases energy
products have lower PE than reactants
energy released
2H2(l) + O2(l)  2H2O(g) + energy

4. C. Endothermic Reaction
reaction that absorbs energy
reactants have lower PE than products
energy absorbed
2Al2O3 + energy  4Al + 3O2

5. 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

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

7. A. Collision Theory Activation Energy (Ea)
minimum energy required for a reaction to occur
Activation
Energy

8. A. Collision Theory Activation Energy depends on reactants
low Ea = fast rxn rate Ea

9. B. Factors Affecting Rxn Rate
Surface Area
high SA = fast rxn rate
more opportunities for collisions
Increase surface area by…
using smaller particles
dissolving in water

10. B. Factors Affecting Rxn Rate
Concentration
high conc = fast rxn rate
more opportunities for collisions

11. B. Factors Affecting Rxn Rate
Temperature
high temp = fast rxn rate
high KE
fast-moving particles
more likely to reach activation energy

12. B. Factors Affecting Rxn Rate
Temperature
Analogy: 2-car collision
5 mph “fender bender”
50 mph “high-speed crash”

13. B. Factors Affecting Rxn Rate
Catalyst
substance that increases rxn rate without being consumed in the rxn
lowers the activation energy

14. B. Factors Affecting Rxn Rate
Enzyme Catalysis