1. Announcements Handouts on back tables
Exams handed back in lab this week.
Very Useful Video: How to analyze dye kinetics lab data (link on course web site)

2. A rate law must be determined by experiment
Method 1: Initial Rates
Vary one thing at a time, keep temperature constant
If concentration doubles and:
Rate does not change
Rate doubles
Rate quadruples
General Rule:

3. Simulation: Concentration dependence of reaction rates
Starting Concentration
Initial Rate
Order of Reaction
A→ B
C→ D
E→ F

4. Example: The initial rate method with >1 reactant

5. What is k for 2NO2 + O2 →2NO2? (use experiment 4 data)
284 M/s
7094 M/s
1.4 x 10-4 M/s
0.004 M/s

6. A rate law must be determined by experiment
Method 2: Using Concentration vs. Time Graphs
The graph of [R] vs. time will depend upon the reaction order
Data from zero, first, and second order reactions will all look different when graphed
Take experimental data, graph it different ways, look for which graph looks linear

7. What does the concentration vs
What does the concentration vs. time graph look like for a zero order reaction?

8. What does the concentration vs
What does the concentration vs. time graph look like for a first order reaction?

9. What does the concentration vs
What does the concentration vs. time graph look like for a second order reaction?

10. We can use rate laws to determine an unknown quantity
We MUST know the order of the reaction
Four variables:
k, rate constant
[R]0, initial concentration of reactant
[R]t, concentration of reactant after time
t elapsed time
If you know the reaction order and three of these, you can find the fourth

11. Example: Using the rate law for a first order reaction to determine [reactant] after an amount of time

12. Example: Using the rate law for a second order reaction to determine the rate constant k
The decomposition of nitrous oxide at 565 oC,
2 N2O  2 N2 + O2
is second order in N2O. If the reaction is initiated with [N2O] equal to M,
and drops to M after 1250 s have elapsed, what is the rate constant?

13. Flashback: There are two methods for determining and using the rate law
Method 1: Initial rate
Method 2: Graphical
Collect [R] over an interval of times
Make plots of:
[R] vs. time
ln[R] vs. time
1/[R] vs. time
Only one will be linear. → reaction order
Slope of linear plot = rate constant

14. The rate law equations can be rearranged in the form of an equation for a line

15. What does the concentration vs
What does the concentration vs. time graph look like for a zero order reaction?

16. What does the concentration vs
What does the concentration vs. time graph look like for a first order reaction?

17. What does the concentration vs
What does the concentration vs. time graph look like for a second order reaction?

18. Using the graphical method on a real example- decomposition of H2O2
2 H2O2  2 H2O + O2
Use Excel (or other spreadsheet program) to make graphs of
time vs. [H2O2]
time vs. ln[H2O2]
time vs. 1/[H2O2]