Unit 7 Notes
Part 1
Chemical Kinetics
• The area of chemistry
concerned with the speed at
which reactions occur is called
chemical kinetics.
– Reaction rate is the change
in concentration of
reactants and products in a
certain amount of time.
Average rate of reaction =
Δ [reactant or product]
Δ time
Collision Theory
Key Idea: Molecules must collide to react.
•In order to react molecules and atoms must come in
contact with each other.
•They must hit each other hard enough to react.
•Anything that increase these will make the reaction
occur faster.
Energy
Reactants
Products
Reaction coordinate
Energy
Activation Energy Minimum energy to
make the reaction
happen
Reactants
Products
Reaction coordinate
Energy
Reactants
Overall energy
change
Products
Reaction coordinate
Endothermic Reactions
Exothermic Reactions
Your To-Do List for Today
• Work independently and quietly!
• In your books:
• Read & take notes on “Reaction Rates” on pg.
722-724
• Answer Question #1 on pg 731
• Read & take notes on 22-2 on pg. 732-737
• Answer Questions #1,2,5 on pg. 737
• Read & take notes on 22-3 on pg. 738-743
• Answer Questions #1-3
• DUE MONDAY!!
2NO2(g)  2NO(g) + O2(g)
Reaction Rates:
1. Can measure
disappearance of
reactants
2. Can measure
appearance of
products
3. Are proportional
stoichiometrically
4th Period- Get out homework for
grading!
DMA#8
4/15/13
Name 3 things that could
increase the rate at
which a chemical
reaction happens.
•Catalyst: A substance that
speeds up a reaction
without being consumed
•Enzyme: A large molecule
(usually a protein) that
catalyzes biological
reactions.
Catalysts
H H
• Hydrogen bonds to surface
of metal.
• Break H-H bonds
H
H
Pt surface
H H
H H
Catalysts
H
H
H
C
C
H
H H
H
H
Pt surface
Catalysts
• The double bond breaks and bonds to the
catalyst.
H
H
H
C
H
C
H
H
Pt surface
H H
Catalysts
• The hydrogen atoms bond with the carbon
H
H
H
C
H
C
H
H
Pt surface
H H
Catalysts
H
H
H
H
C
C
H
H
H
Pt surface
H
Catalysts increase the number of
effective collisions.
Exothermic Reaction with a Catalyst
 This is the same graph you sketched last time, so you can
just add the new catalyst activation energy.
Endothermic Reaction with Catalyst
Energy Diagrams
1. Draw and label an energy diagram. Calculate the
activation energy and change in energy of the
reaction
• Reactants = 78.9 kJ
• Products = 125.3 kJ
• Activated complex = 300 kJ
• Reactants = 25.1 kJ
• Products = 35.2 kJ
• Activated complex = 49.0 kJ