Consider the following reaction:
a) Express the rate of this reaction in terms of concentrations of and D .
b) At some point in the reaction and 13.20 minutes later .
Based on this data, what is the average rate of the reaction during this time in ?
c) In one experiment, the rate of change of B was found to be . What is the rate of change of C in this experiment?
The following data was collected for the reaction shown below:
Expt.
M
M
Initial Rate
1
0.105
0.15
2
0.105
0.30
3
0.052
0.30
Determine the rate law for this reaction.
Compare experiments 2 and 3:
With [ ] constant, as [ ] is halved, rate is halved.
Therefore rate is first order with respect to
Compare experiments 1 and 2:
With [ ] constant, as [ ] is doubled, rate increases by 4 times.
Therefore rate is second order with respect to
The following data was collected for the reaction shown below:
Expt.
M
M
Initial Rate
1
0.185
0.133
2
0.185
0.266
3
0.370
0.133
4
0.370
0.266
????
a) Determine the rate law for this reaction.
Compare experiments 1 and 3:
With constant, as is doubled, rate is doubled.
Therefore rate is first order with respect to [A];
Compare experiments 1 and 2:
With constant, as is doubled, rate increases by 4 times.
Therefore rate is second order with respect to [B]; y=2
b) Calculate the value of k for this reaction.
Insert data from any experiment into the rate equation to calculate
c) Calculate the rate of experiment 4 .
Or
Since both and are doubled compared to experiment 1, rate would be expected to be 8 times rate in experiment 1. Therefore
Rate
4. The thermal decomposition of to form and is a first order reaction. The rate constant for the reaction is at 318 K . Calculate the half-life of this reaction.
The thermal decomposition of phosphine to phosphorus and hydrogen gas is a first order reaction, with a half-life of 35 s at .
a) Calculate the rate constant for this reaction.
b) Calculate the time required for of phosphine to decompose.
The rate constant for the order reaction shown below is at . How many seconds would it take for the concentration of to decrease from 0.62 M to 0.28 M ?
The gas phase decomposition of to form NO and was studied at and the following data was collected:
Time
0.0
0.100
5.0
0.017
10.0
0.0090
15.0
0.0062
20.0
0.0047
Determine the order of this reaction with respect to [ ] and calculate the rate constant.
Plot a graph of vs. time and vs. time.
Since plot of vs. time give a straight line, this reaction is second order with respect to [ ]
The rate constant, , is the slope of the plot.
The reaction has an activation energy of and an enthalpy of . Sketch a potential energy diagram for this reaction and determine the activation energy for the reverse reaction?
The activation energy for the reverse reaction is
9. Shown below is an Arrhenius plot for the reaction:
Based on this information, determine the activation energy ( ) and the frequency factor (A) for this reaction. (Estimate your calculations to 3 sig figs)
The reaction was studied and the following mechanism was proposed:
(1) (fast)
(2) (slow)
Determine the rate law based on this mechanism.
From reaction (2)
From reaction (1)
Substituting into reaction (2)
Assuming the activation energies are equal, which of the following reactions will occur at a higher rate at ? (Hint: What factors affect the rate of a reaction)
At , both and would have the same kinetic energy, but since has a larger molar mass than , its molecules would have lower average speed, leading to lower collision frequency and lower reaction rates.
Also, since is a more complex molecule, it would probably have lower orientation probability, reducing its reaction rate even further.
12. The following rate data was collected for the reaction shown below:
Exp. #
Initial Rate
1
0.50
1.50
2
1.50
1.50
3
3.00
3.00
Determine the Rate Law and calculate the rate constant ( k ) for this reaction.
Compare experiments 1 and 2:
With constant, as is tripled, rate is tripled.
Therefore rate is first order with respect to [A];
Compare experiments 2 and 3:
As and are both doubled, rate increases by 4 times. Factoring the effect of (doubling rate since it is first order) the effect of would be doubling of rate due to doubling of concentration.
Therefore rate is first order with respect to [B]; y=1
The following mechanism has been proposed for reaction of HBr with to form and
a) Identify all reaction intermediates in this reaction.
Reaction intermediates are HOOBr and HOBr
b) Write a balanced overall equation for this reaction. (Hint: you may have to multiply all the coefficients of an elementary reaction before adding)
Multiply the third equation by 2 and add all equations:
overall equation
14. The following mechanism has been proposed for the reaction of NO with to form and .
The observed rate law for this reaction is: Rate . If the proposed mechanism is correct, what can we conclude about the relative speeds of the first and the second steps?
If the first reaction was the slow step,
If the second reaction was the slow step,
Since is an intermediate it cannot be in the rate law, therefore
From first reaction: and
Substituting for Rate
Since the predicted rate law for the second assumption matches the observed rate law, it is correct.
15. The reaction below has been studied and the following experimental rate law determined:
Three mechanisms have been proposed for this reaction. Predict the rate law based on each mechanism and determine which is consistent with the experimental rate law?
a)
b) (slow) (fast)
Rate ICl
c) (fast) (slow)
From first reaction:
Substituting for Rate
The predicted rate law from mechanism (b) matches the observed rate law, therefore mechanism (b) is correct.
16. The following mechanism has been proposed for the catalyzed oxidation of thallium (I) by cerium (IV):
a) Identify the catalyst and the intermediates in this mechanism.
Since is used in the first step and generated in the last step, it is the catalyst. and are both generated in one step and used in another step, therefore they are intermediates.
b) Determine the overall equation for this reaction.
Overall equation:
c) Explain why the reaction would be slow without the catalyst.
Without a catalyst, this reaction would be termolecular which would be expected to occur very slowly
