Chemical Kinetics

Chemical Kinetics, Chemical Equilibrium & Acids and Bases

1. The following data were collected for the rate of disappearance of NO in the reaction 2NO(g)+O2(g)-----> 2NO2(g)

Experiment [NO](M) [O2](M) Initial Rate(M/s)
1 0.0126 0.0125 1.41 x 10^-2
2 0.0252 0.0250 1.13 x 10^-1
3 0.0252 0.0125 5.64 x 10^-2

a) What is the rate law for the reaction?
b) What are the units of the rate constant?
c) What is the average value of the rate constant calculated from the three data sets?
d) What is the rate of disappearance of NO when [NO]= 0.100 M and [O2]= 0.0200 M?
e) What is the rate of disappearance of O2 at the concentrations given in part (d)?

2. From the following data for the first-order gas-phase isomerization of CH3NC at 215 degrees Celsius, calculate the first-order rate constant and half-life for the reaction:

Time(s) Pressure CH3NC(torr)
0 502
2000 335
5000 180
8000 95.5
12000 41.7
15000 22.4

3. a) The activation energy for the isomerization of methyl isonitrile is 160kJ/mol. Calculate the fraction of methyl isonitrile molecules that have an energy of 160.0kJ or greater at 500 K.
b) Calculate this fraction for a temperature of 510 K. What is the ratio of the fraction at 510 K to that at 500 K?

4. The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism.
H2O2(aq)+ I-(aq)--->H2O(l)+ IO-(aq) [slow]
IO-(aq) + H2O2(aq)--->H2O(l) + O2(g) + I-(aq) [fast]

a)Write the rate law for each of the elementary reactions of the mechanism.
b) Write the chemical equation for the overall process.
c) Identify the intermediate, if any, in the mechanism.
d) Assuming that the first step of the mechanism is rate determining, predict the rate law for the overall process.

5. Cyclopentadiene(C5H6) reacts with itself to form dicyclopentadiene (C10H12). A 0.0400M solution of C5H6 was monitored as a function of time as the reaction 2 C5H6-----> C10H12 proceeded. The following data was collected:
Time(s) [C5H6](M)
0.0 0.0400
50.0 0.0300
100.0 0.0240
150.0 0.0200
200.0 0.0174

Plot [C5H6] versus time, In [C5H6] versus time, and 1/[C5H6] versus time. What is the order of the reaction? What is the value of the rate constant?

6. a) Two reactions have identical values for Ea(activation energy). Does this ensure that they will have the same rate constant if run at the same temperature? Explain.
b)Two similar reactions have the same rate constant at 25 degrees Celsius, but at 35 degrees Celsius one of the reactions has a higher rate constant than the other. Account for these observations.

7. Consider the following equilibrium, for which Kp=0.0752 at 480 degrees Celsius:
2 Cl2(g) + 2 H2O(g)----> 4 HCl(g) + O2(g)
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a) What is the value of Kp for the reaction
4 HCl(g) + O2(g)----> 2 Cl2(g) + 2 H2O(g)?
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b) What is the value of Kp for the reaction
Cl2(g) + H2O(g)-----> 2 HCl(g) + 1/2 O2(g)?
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c) What is the value of Kc for the reaction in part b?

8. Phosphorous trichloride gas and chlorine gas react to form phosphorous pentachloride gas:
PCl3(g)+ Cl2(g)-----> PCl5(g)
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A gas vessel is charged with a mixture of PCl3(g) and Cl2(g), which is allowed to equilibrate at 450 K. At equilibrium the partial pressures of the three gases are PpCl3= 0.124 atm, PCl2= 0.157atm, and PpCl5= 1.30atm.
a) What is the value of Kp at this temperature?
b) Does the equilibrium favor reactants or products?

9. Kp for the equilibrium
N2(g) + 3 H2(g)----->2 NH3(g)
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is 4.51 x 10^-5 at 450 degrees Celsius. For each of the mixtures listed below, indicate whether the mixture is at equilibrium at 450 degrees Celsius. If it is not at equilibrium, indicate the direction (toward product or toward reactants) in which the mixture must shift to achieve equilibrium.
a) 105atm NH3, 35atm N2, 495atm H2
b) 35atm NH3, 595atm H2, no N2
c) 26atm NH3, 42atm H2, 202atm N2

10. Methanol (CH3OH) can be made by the reaction of CO with H2:
CO(g) + 2 H2(g)----> CH3OH(g)
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a) Use thermochemical data to calculate H for this reaction.
b) In order to maximize the equilibrium yield of methanol, would you use a high or low temperature?
c) In order to maximize the equilibrium yield of methanol, would you use a high or low pressure?

11. At 1200 K, the approximate temperature of automobile exhaust gases, Kp for the reaction, 2 CO2(g)----> 2 CO(g) + O2(g)
<----
is about 1 x 10^-13. Assuming that the exhaust gas(total pressure 1atm) contains 0.2% CO, 12% CO2, and 3% O2 by volume, is the system at equilibrium with respect to the above reaction? Based on your conclusion, would the CO concentration in the exhaust be decreased or increased by a catalyst that speeds up the reaction above?

12. Complete the following table by calculating the missing entries. In each case indicate whether the solution is acidic or basic:

pH pOH [H+] [OH-] Acidic or Basic?
4.75
11.89
6.5 x 10^-3M
8.6 x10^-7M

13. Calculate the pH of each of the following strong acid solutions:
a) 0.00835 M HNO3
b) 0.525 g of HClO4 in 2.00 L of solution
c) 5.00 mL of 1.00 M HCl diluted to 0.500 L
d) A mixture formed by adding 50.0 mL of 0.020 M HCl to 150 mL of 0.010 M HI.

14. A 0.100 M solution of bromoacetic acid (BrCH2COOH) is 13.2% ionized. Calculate [H+], [BrCH2COO-], and [BrCH2COOH].

15. Determine the pH of each of the following solutions:
a) 0.125 M hypochlorous acid
b) 0.0085 M phenol
c) 0.095 M hydroxylamine

16. We can calculate Kb for the carbonate ion if we know the Ka values of carbonic acid(H2CO3).
a) Is Ka1 or Ka2 of carbonic acid used to calculate Kb for the carbonate ion? Explain.
b) Calculate Kb for the carbonate ion.
c) Is the carbonate ion a weaker or stronger base than ammonia?

17. Codeine(C18H21NO3) is a weak organic base. A 5.0 x 10^-3 M solution of codeine has a pH of 9.95. Calculate the value of Kb for this substance. What is the pKb for this base?

18. Explain the following observations:
a) HCl is a stronger acid than H2S
b) H3PO4 is a stronger acid than H3AsO4
c) HBrO3 is a stronger acid than HBrO2
d) H2C2O4 is a stronger acid than HC2O4-
e) Benzoic acid (C6H5COOH) is a stronger acid than phenol (C6H5OH)

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