TUTORIAL 8: REACTION KINETICS
1.
(a)
Define reaction rate. rate.
(b)
Write the differential rate equation for the following reactions.
2.
i.
I(aq) + OCl(aq) Cl(aq) + OI(aq)
ii.
3O2(g) 2O3(g)
iii.
4NH3(g) + 5O2(g) 4NO(g) + 6H 2O(g)
For the reaction 4NH3(g) + 5O2(g) 4NO(g) + 6H 2O(g) the rate of disappearance of oxygen is 0.020 Ms -1
3.
(a)
i.
Determine the rate of formation of H2O and
ii.
the rate of dissappearance of NH3
Explain the following terms.
(b)
i.
rate law
ii.
rate constant
iii.
half-life
Consider the reaction: A product i.
Write the rate law .
ii.
Determine the unit of rate constant.
iii.
Sketch the graphs of rate of reaction versus concentration of A for zero, first and second order reactions.
The reaction of peroxydisulfate ion (S 2O82-) with iodide ion (I -) is S2O82- (aq) + 3I - (aq) → 2SO42- (aq) + I 3-(aq)
4.
-
-
-
Experiment
[S2O8 ]
[I ]
Initial rate (Ms )
1
0.080
0.034
2.2 x 10
-
2
0.080
0.017
1.1 x 10
-
3
0.160
0.017
2.2 x 10
-
From the following data collected at certain cert ain temperature, a) calculate the order with respect to each reactants b) determine the rate constant c) write the rate equation
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TUTORIAL 8: REACTION KINETICS
5.
The conversion of cyclopropane to propene in the gas phase is a first order reaction -4 1 with a rate constant of 6.7 10 s at 500C. CH2
H2C
6.
CH2
H2C
CH
CH3
(a)
If the initial concentration of cyclopropane was 0.25 M, calculate the concentration after 8.8 min.
(b)
How long will it take for the concentration of cyclopropane to decrease from 0.25 M to 0.15 M?
(c)
How long will it take to convert 74% of the starting material to propene?
Iodine atoms combine to form molecular iodine in the gas phase: I(g) + I(g) I2(g) The rate constant for the above reaction is 7.0 109 M1 s1 at 23C.
7.
(a)
If the initial concentration of iodine atoms is 0.086 M, calculate the concentration after 2.0 min.
(b)
Calculate the half-life of iodine atoms if the initial concentration is i.
0.42 M
ii.
0.60 M – 4 – 1
The decomposition of dinitrogen pentoxide with the rate constant of 5.1 10 45oC is given below:
s
at
2N2O5(g) 4NO2(g) + O2(g) (a)
Calculate the concentration of N2O5 after 3.2 min if the initial concentration is 0.25 M.
(b)
If the initial concentration of N2O5 is 0.35 M, calculate the time needed for the concentration to be reduced i.
to 0.08 M.
ii.
by 62%.
8. A catalytic reaction of ammonia gas decomposes into nitrogen gas and hydrogen gas with a platinum catalyst is one example of zero or der reaction. In one reaction, the initial concentration of ammonia gas is 1.5 M and after 120 seconds the concentration is 0.75 M. a) Calculate the : i) rate constant ii) half life b) If the original concentration is reduced to 1.0 M, does the half- life decrease, increase, or stay the same? If the half-life changes what is the new half-life?
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TUTORIAL 8: REACTION KINETICS
9.
The data listed in the table below were obtained from the following decomposition : A products
10.
1
Time/min
[A]/M
ln [A]
0
1.00
0.00
1.00
5
0.63
0.46
1.60
10
0.46
0.78
2.20
15
0.36
1.02
2.80
25
0.25
1.39
4.00
[A]
(a)
Establish the order of the reaction by graphical method.
(b)
Determine the rate constant , k.
(c)
Determine the half-life, t1/2, if [A]0 = 1.00 M.
a) What are the conditions for an effective collision to occur between reactant molecules to form product? b) How does transition state theory describe activated complex and activation energy?
11.
Explain the effect of temperature on reaction rate based on Maxwell-Boltzmann distribution curve.
12.
The following equation shows the decomposition of HI(g): Pt
2HI(g)
H2(g) + I2(g)
ΔH = -ve
(a)
What is the function of platinum?
(b)
Draw and label the potential energy profile for the reaction with and without platinum.
(c)
Give another two factors that can influence the reaction rate and explain your answer.
13.
The rate constant of a reaction is 3.4610-2 s1 at 298 K. Calculate the rate constant at 350 K if the activation energy for the reaction is 50.2 kJ mol1.
14.
(a)
What is meant by activation energy?
(b)
The rate constant of a reaction at 463 K is 2.52105 s1 and at 503 K is 6.30104 s1. Determine the activation energy for the react ion.
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TUTORIAL 8: REACTION KINETICS
15.
Rate constants, k for decomposition of hydrogen iodide at different temperatures are given in the table below : Rate constant, k ( mol1 dm3 s1)
Temperature (K)
9
500
6
600
3
700
2
800
3.7510 6.6510 1.1510 7.7510 (a)
Write the Arrhenius equation.
(b)
Determine the activation energy for the decomposition of hydrogen iodide graphically from the above data. [ The gas constant, R = 8.314 JK -1 mol-1]
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TUTORIAL 8: REACTION KINETICS
OBJECTIVE QUESTIONS 1.
The rate of formation of water from the reaction: 2MnO4(aq) + 6H+(aq) + 5H2O2(aq) 2Mn2+(aq) + 8H2O(l ) + 5O2(g) is 0.035 M s -1. What is the rate of H2O2 being reacted?
2.
4
8.7510 M s
B.
2.19103 M s1
C.
8.7510 3 M s
D.
2.1910 M s
1
2
1
For the reaction: A + 2 B C + 2 D, the initial rate, is the value of
3.
1
A.
d[ B]
dt
dt
is 2.6102 M s1. What
?
A.
6.5103 M s1
B.
1.3102 M s1
C.
2.610 M s
D.
5.2102 M s1
2
d[ A]
1
In the rate law, Rate = k[NO] [O2], the reaction is _____ order for NO, _____ order for O2, and_____ order overall. (a) second; first; third (b) second; zero; third (c) first; second; third (d) first; third; first
4.
The slow rate of a particular chemical reaction might be attributed to which of the following? (a) a low activation energy (b) a high activation energy (c) the presence of a catalyst (d) the temperature is high
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TUTORIAL 8: REACTION KINETICS
5.
The reaction A + B
→
C +
D follows the rate law: Rate = k [A].
What will be the effect of decreasing the concentration of A? (a) The rate of the reaction will increase (b) More D will form (c) The rate of the reaction will decrease (d) The reaction will shift to the left
6.
The energy difference between the reactants and the transition state is (a) the free energy (b) the heat of a reaction (c) the activation energy (d) the kinetic energy
7.
The decomposition of ammonia to its elements is a first-order reaction with a half-life of 200 seconds at a certain temperature. How much time will it take for the partial pressure of ammonia to decrease from 0.100 atm to 0.00625 atm? (a) 200 sec (b) 400 sec (c) 800 sec (d) 1000 sec
8.
The specific rate constant, k, for radioactive beryllium-11 is 0.049 sec-1. What mass of a 0.500 mg sample of beryllium-11 remains after 28 seconds? (a) 0.250 mg (b) 0.125 mg (c) 0.0625 mg (d) 0.503 mg
9.
A reaction follows the rate law: Rate = k[A] 2. Which of the following plots will give a straight line? (a) 1/[A] versus 1/time (b) [A] 2 versus time (c) 1/[A] versus time (d) ln[A] versus time (e) [A] versus time 6
TUTORIAL 8: REACTION KINETICS
10.
A 100-gram sample of pure 37Cl decays by electron capture with a half-life of 35 days. How long will it take for 90 grams of 37Cl to accumulate? (a) 31 days (b) 5.32 days (c) 78 days (d) 116 days
11.
12.
If activation energy, E a for a certain biological react ion is 50 kJ mol1, how many times will the rate of the reaction increase when body temperature increases from 37C to 40C? A.
1.00
B.
1.15
C.
1.20
D.
2.00
2 NO (g) + O2 (g) → 2 NO2 (g) The reaction above occurs by the following two-step process: Step I: NO (g) + O2 (g) → NO3 (g) Step II: NO3 (g) + NO (g) →2 NO2 (g) Which of the following is true of Step II if it is the rate-limiting step? (a) Step II has a lower activation energy and occurs more slowly than Step I. (b) Step II has a higher activation energy and occurs more slowly than Step I. (c) Step II has a lower activation energy and occurs more quickly than Step I. (d) Step II has the same activation energy and occurs at the same speed as Step I.
13.
2 NO (g) + 2 H2 (g) → N2 (g) + 2 H2O (g) Which of the following is true regarding the relative molar rates of disappearance of the reactants and the appearance of the products? I.
N2 appears at the same rate that H2 disappears.
II.
H2O appears at the same rate that NO disappears.
III. NO disappears at the same rate that H2 disappears.
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TUTORIAL 8: REACTION KINETICS
14.
The reaction : Q products is believed to be of first order. Which of the following graph(s) is/are correct? I. ln[Q]
t
II [Q]
t
III Rate
[Q]
8
