NATIONAL OPEN UNIVERSITY OF NIGERIA
14/16 AHMADU BELLO WAY, VICTORIA ISLAND, LAGOS
SCHOOL OF SCIENCE AND TECHNOLOGY
MARCH/APRIL 2014 EXAMINATION
COURSE CODE: CHM 407
COURSE TITLE: REACTION KINETICS
TIME ALLOWED: 2 Hours 30minutes
INSTRUCTION: Answer any four questions
Q1
(a) Explain how a catalyst affects the rate of a reaction. (4 marks)
(b) The decomposition of hydrogen iodide on gold at 323 K is zeroth order reaction and the rate constant is 1.20 ×l0-4 M s-1
(i) If the initial concentration of hydrogen iodide is 0.500 M, calculate its concentration after 3.00 × 103 s. (4 marks)
(ii) How long will it take for all of the hydrogen iodide to decompose? (5 marks)
(c) Consider the following experiments, each involving equal masses of zinc and
10.0 mL of acid:
Identify the fastest and the slowest reactions. Explain your answer. (5 marks)
Q2
(a) What do you understand by the following terms?
(i) Physisorption (ii) Chemisorption (5 marks)
(b) List any THREE assumptions of the Langmuir Adsorption Isotherm (4½ marks)
(c) List THREE modern methods of surface studies (3 marks)
(d) (i) What is a catalyst? (2 marks)
(ii) List the three known types of catalysts (3 marks)
Q3
(a) (i) At 323 K, the rate of reaction for the decomposition of N2O5 at a particular instant is 2.74 ×10-4 M s-1. Calculate the rate of formation of O2. The reaction is represented below:
2N2O5(g) → 4 NO2 (g) + O2 (g) (3 marks)
(ii) In the decomposition of hydrogen iodide, what is the relationship between the rate of decomposition of HI and the rate of formation of H2? (2 marks)
(b) An experiment is done to determine the rate of the following reaction:
2Al(s) + 6HCl(aq) ® 3H2(g) + 2AlCl3(aq)
(i) Calculate the rate of formation of H2 in g/sec (3 marks)
(ii) Calculate the rate of formation of H2 in mol/min. (3 marks)
(iii) Calculate the rate of consumption of Al in g/sec. (3 marks)
(c) Consider the following mechanism for a reaction:
Step 1: HBr + O2 ® HOOBr
Step 2: HBr + HOOBr ® 2HOBr
Step 3: 2HOBr + 2HBr ® 2Br2 + 2H2O
Identify the (i) reactant, (ii) product, (iii) catalyst and (iv) intermediate in the reaction.
(4 marks)
Q4
(a) Consider the following reaction:
2H2O2(l) ® 2H2O(l) + O2(g)
Identify the graph that shows the relationship between rate of consumption of H2O2 and time; explain your answer (5 marks).
(b) On heating cyclopropane to 770 K, it is converted into propene. In one experiment, the following data were obtained:
| T (secs) | 0 | 300 | 600 | 900 |
| [Cyclopropane] (M) | 1.50 ×10-3 | 1.24 ×10-3 | 1.00 ×10-3 | 8.3 ×10-4 |
(i) Using graphical method, test whether the above data satisfy first order rate equation.
(6 marks)
(ii) Calculate the rate constant (2 marks).
(c) Consider the first order reaction
A ® products, which has a rate constant, k = 2.95 x10-3 s-1. What percent of A remains after 150 s ? (5 marks)
Q5
(a) Discuss briefly any FOUR experimental methods of rate studies (2½ marks each; = 10 marks)
(b) State the name of a suitable experimental method that can be used to monitor the reaction rate in each following cases. (1½ marks each; = 4½ marks)
(i) H2 (g) + Br2(g) → 2HBr (g)
Hint: Bromine absorbs strongly in the visible region, while hydrogen and hydrogen bromide do not.
(ii) CH3COOC2H5 (aq) + OH ¯ (aq) → CH3COO¯ (aq) + C2H5OH (aq)
(iii) CH3CHO (g) → CH4 (g) + CO (g)
(c) An elementary reaction, 2 A + C ® D, is second order in A and first order in C. The rate of this reaction is 2.5 x 10-1 M/s when the concentrations of A, C, and D are all 1.00 mM. What is the rate constant for the reaction? (3 marks)
Q6
(a) What do you understand by the terms: order and molecularity. Distinguish between the two. (5 marks)
(b) (c) Consider the following reaction:
CaCO3(s) + 2H+(aq) ® Ca2+(aq) + H2O(l) + CO2(g)
(i) List and discuss briefly (using collision theory), four factors that would increase the rate of the above reaction. (2 marks each; = 8 marks)
(c) The rate constant for the reaction
H2(g) + I2(g) ® 2HI(g)
is 5.4 x 10-4 M-1s-1 at 326 oC. At 410 oC the rate constant was found to be 2.8 x 10-2 M-1s-1.
Calculate
(i) the activation energy (ii) the pre-exponential factor, A (5 marks)
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