1. Announcements Welcome back!
me this week if your Exam #2 score was <70
FYI- Exam #3 is one week from Friday (April 23rd)
Review session: Wednesday, April 5:00pm

2. Graphical Form Two point form
The Arrhenius equation is used to determine the activation energy (Ea) from experimental data
Graphical Form
Two point form

3. Using the graphical method to find Ea

4. Example: A reaction triples its rate when the temperature increases from 25 oC to 37 oC. What is the activation energy?

5. Example: A reaction has Ea = 75 kJ/mol. If k = 1
Example: A reaction has Ea = 75 kJ/mol. If k = 1.50 x 10-3 at 25 oC, what is k at 50 oC?

6. A reaction mechanism is the pathway from reactants to products
Elementary step: a discrete step along a reaction pathway
Overall reaction: the sum of a series of elementary steps
“Molecularity”: the number of molecules involved in a step
Unimolecular
Biomolecular
Termolecular (very rare)

7. A catalyst can speed up a reaction
Intermediate: Produced in one step as a product and used as a reactant in another
Catalyst: Used as a reactant in one step and produced as a product in another

8. Example: Identifying overall reaction and intermediates/catalysts

9. What intermediate(s) occur in the following reaction?
N2O2
H2O
N2O2 and H2
N2O2 and H2O
N2O and H2O
N2O2 and N2O
There are none

10. What acts as a catalyst in the following reaction?
N2O2 H2
N2O
H2O
There is no catalyst

11. The rate of an overall reaction is the rate of its slowest (rate determining) step
Each elementary step has its own rate
The rate determining step is the step with the slowest rate

12. The rate law for an elementary step is given by the equation for that step
Molecularity
Rate Equation
A → product
Unimolecular
Rate= k[A]
A + B → product
Biomolecular
Rate= k[A][B]
A + A → product
Bimolecular
Rate= k[A]2
2A + B → product
Termolecular
Rate= k[A]2[B]

15. Proposed mechanism 1: Proposed mechanism 2:
Step 1:
H2 + ICl → HI + HCl (slow)
Step 2:
ICl + HCl → HI + Cl2
Sum
Rate
Step 1
Step 2
Overall
Proposed mechanism 2:
Step 1:
H2 + ICl → HCl + HI (slow)
Step 2:
HI+ ICl → HCl + I2
Sum
Rate
Step 1
Step 2
Overall
How to determine if a proposed reaction mechanism is “reasonable” H2 + 2ICl → 2HCl + I2