1. Announcements Exams handed back in lab this week.
Answer key will be posted on Wednesday.
Video: How to analyze dye kinetics lab data (link on course web site)
Exam #2 Results- Class average = 68

2. Collision theory is a qualitative explanation of how reactions occur and why rates differ
Reactions occur when
Molecules collide…
In the correct orientation…
With enough energy
Consider: NO + O3  NO2 + O2
Molecules collide
Bonds are
formed and
break
product molecules
separate

3. How does rate respond to different things?
For an increase in . . .
The rate . . .

4. We’ll consider rate dependence with regards to these categories…
Concentration
Rate Laws
Concentration vs. Time Relationships
Temperature and Activation Energy
Mechanism

5. Rate laws express the concentration dependence of reactions
A general rule …
Mechanism matters
The bottom line:
You can’t predict the rate law! You have to do experiments

6. There are different types of rates
In general, a rate is the change in concentration of something with time
Rate over time
Instantaneous rate
Initial rate

7. Example- Measuring different types of rates

8. Rate Laws (also called Rate Equations)
first order reaction
For the reaction: 2 N2O5  4 NO + O2
Rate = k[N2O5]
For the reaction: NO2  NO + ½ O2
Rate = k[NO2]2
For the reaction: CO + NO2  CO2 + NO
Rate = k[CO][NO2]
second order reaction
first order in CO and in NO2; second order overall

9. Here is what a “rate law” looks like
First order reaction
2 N2O5  4 NO + O2
Second order reaction
NO2  NO + ½ O2
First order in CO and NO2, second order overall
CO + NO2  CO2 + NO
Zero order

10. If the rate law of a reaction is Rate=[A][B]2 , how what is the order with respect to A?
Zero
First
Second
Third

11. Zero First Second Third
If the rate law of a reaction is Rate=[A][B]2 , how what is the overall order of the reaction?
Zero
First
Second
Third