1. Not a straight line!!!! Therefore, not zero order.
2N2O NO2(g) O2(g)
Not a straight line!!!! Therefore, not zero order.

2. Not a straight line!!!! Therefore, not 2nd order
2N2O NO2(g) O2(g)
Not a straight line!!!! Therefore, not 2nd order

3. Find the [N2O5] present at 15 minutes into the reaction.
2N2O NO2(g) O2(g)
Produces the best straight line…therefore the reaction is first order and the rate law is Rate = k [N2O5]
ln [N2O5] = -2.3
[N2O5] = 0.10
k = min-1
Find the [N2O5] present at 15 minutes into the reaction.
[N2O5] = M at 15 minutes
ln [N2O5] = -kt + ln [N2O5]0

4. How long does it take to use up 10.0% of the N2O5?
2N2O NO2(g) O2(g)
How long does it take to use up 10.0% of the N2O5?
t = 3.5 min.
k = min-1
Find the [N2O5] present at 15 minutes into the reaction.
[N2O5] = M at 15 minutes
ln [N2O5] = -kt + ln [N2O5]0
ln ([N2O5]/[N2O5]0)= -kt

5. N2O5(g)  2NO2(g) ½O2(g)
First order in N2O5 (known from previous example)
Dinitrogen pentoxide decomposes when heated. If the rate constant for the decomposition of N2O5 is 6.2 x 10-4/min, what is the half-life? How long would it take for the concentration of the N2O5 to decrease to 25% of its initial value? …to 12.5% of its initial value
Time needed for the original concentration to be cut in half.
t½ = 1100 min.
…to 25% of initial [ ] = min. (two half-lifes)
…to 12.5% of initial [ ] = min. (three half-lifes)

6. Rate = k [ClO2]m[ I-]n = k' [ClO2]m
2ClO2(aq) I-(aq)  2ClO2-(aq) I2(aq)
If [ I-] is quite large with respect to [ClO2]…
k' = k [ I-]n
Rate = k [ClO2]m[ I-]n
= k' [ClO2]m
If you needed to determine the order of the reaction with respect to the ClO2 what would you need to know?
Time [ClO2]
0.00 s M
1.00 s M
2.00 s M
3.00 s M
[ClO2] ln [ClO2]
2.10 x 103 M
2.32 x 103 M
2.55 x 103 M
2.83 x 103 M
Most linear… therefore first order with respect to the chlorine dioxide