Chemistry II-AP
Kinetics worksheet
Consider the kinetics data for the following gaseous reaction:
2 A + B + C -----------> D + E
@ 300 K
......................................................................................................................................
initial
Trial
[A]
[B]
[C]
rate (in M/hr)
1
0.100
0.200
0.200
2.04 x 10-3
2
0.100
0.200
0.400
4.08 x 10-3
3
0.400
0.200
0.400
4.08 x 10-3
4
0.300
0.600
0.200
1.84 x 10-2
5
0.100
0.100
0.100
2.55 x 10-4
6
0.350
0.350
0.350
7
0.200
??
0.400
??
6.04 x 10-4
===================================================================
1. What is the order of the reaction with respect to A? B? C? (3)
A: Trial 2 and 3, concentration gets multiplied by four, but the initial rate stays the same. 4x=1, x=0
B: Trial 1 and 4, concentration stays the same, rate stays the same. 3x=9, x=2
C: Trial 1 and 2, concentration doubles, rate doubles. 2x=2, x=1
2. Write the rate law expression. (1)
Rate= k[B]2[C]
3. What is the overall order of the reaction? (1)
3
4. What is the value of the specific rate constant? [Be sure to include the units!] (2)
Using trial 1, k=2.04E-3/0.23, k=0.255 M/hr
5. If the concentration of B in trial #4 was quadrupled, with the concentrations of the other reactants
remaining the same, what would be the value of the new initial rate? (1)
0.255x 2.42x0.2=0.293
6. What is the rate of the reaction for trial #6? (1)
0.353 x 0.255=0.012 M/hr
7. What is the [B] in trial #7? (1)
b2 x 0.4 x 0.255 = 6.04E-4, b=0.076
8. If the reaction mechanism was believed to occur in 3 elementary steps, with the second step being the
slowest (rate-determining), which reactant is not a factor until the third step and why? (2)
A, this is because a is of the zeroth order so it is not a part of the reaction until the third step
-29. How many hours would it take for a 6.000-gram sample of Rn-230 to decay so that only 0.750 grams of
Rn-230 remains? The half-life of Rn-230 is 48.6 hours for this first-order decay reaction. (2)
-
3 half lives (6, 3, 1.5, 0.75)
3(48.6)=145.8 hours
10. What is the value of the decay rate constant (k) in problem #9? (1)
- k = ln(2) / t1/2 = 0.693 / 48.6 hrs = 0.0143 hours
11. Using the information from problems #9 and #10, how many hours will it take for a 10.00-gram sample
to decay so that only 3.23 grams remains? (1)
- (ln(10/3.23))/0.0143 = 79 hours
12. The reaction:
R + 2 S -------> T + V
occurs in a single step. What is the overall order of the reaction? Why is this most improbable?
For a collision to be considered to be “effective”, what two criteria must be met? (4)
- The order of the reaction is 3rd order. It isn’t probable because for a collision to be deemed effective
it has to collide in a specific direction at a specific angle and there needs to be enough energy in the
collision to break and form new bonds.
..........................................................................
Consider the following reaction and its theoretical mechanism steps:
D + 2 E + F ---------------> G + 2 H
Ni
Step 1:
Step 2:
Step 3:
D + Ni ------------> X
X + E + F ----------> R + 2 H + Ni
R + E ------------> G
13. Which step is the rate-determining step? (1)
Step 2
14. What is the overall order of the reaction? (1)
2nd order
15. What is the catalyst? (1)
Ni
16. What is/are the intermediate(s)? (1)
X, R
fast
slow
moderate