A. Very-Short-Answer Questions
1. What is the unit of the rate of a reaction?
2. How is the order of a reaction related to its stoichiometry?
3. If rate = k[A][B]2 for a reaction, what is the order of the reaction?
4. What are the units for the rate constants of zero order and first-order reactions?
5. What is the order of reaction if the rate constant is 1.35x10-2 mol-2 L2s-1?
6. On what factor does the rate constant of a reaction depends?
7. What is the half-life of a reaction?
8. How is the half-life related to the initial concentration of the reactant for a (i) zero-order reaction, (ii) first-order reaction?
9. The enthalpy of a reaction is 50 kJ. What is the minimum value of the activation energy for the reaction?
10. How does the rate of a zero-order reaction change with time?
B. Short-Answer Questions
1. What do you understand by the rate of a chemical with time?
2. What is the difference between average rate and instantaneous rate?
3. On what factor does the rate of reaction depend?
4. What is the rate law?
5. What is the rate constant?
6. The rate constant of a reaction is 75s-1. What will be the rate constant if the unit of time is the minute?
7. Draw graphs to show the change in the concentration of the reactant with time for a (i) zero-order reaction, (ii) first-order reaction.
8. For a zero-order reaction, how does the length of the first half-life compare with the length of the second half-life?
9. Why do gaseous decomposition reactions on metal surfaces follow zero-order kinetics in the beginning but change to first-order later?
10. What is a pseudo first-order reaction?
11. 1. For a reaction, rate = k[A]2/[B]. What will happen to the rate if the concentration of
(i) A is doubled,
(ii) B is doubled,
(iii) Both A and B are doubled?
12. What do you understand by the mechanism of a reaction?
13. What do you understand by the rate-determining step?
14. What is the molecularity of a reaction?
15. What is activation energy?
16. Why does the rate of reaction increase with rise in temperature?
17. What is the Arrhenius equation?
18. What is the significance of the pre-exponential factor in the Arrhenius equation?
19. How does a catalyst increase the rate of a reaction?
20. Why is it not possible for a catalysed reaction to occur in a single step?
21. What is a transition state?
22. What is a reaction intermediate?
C. Long-Answer Question
1. The reaction A+B → C+D is believed to occur in two steps:
Step 1 (fast): A+B → E
Step 2 (slow): E → C+D
(i) Which is the rate-determining step?
(ii) What is the rate molecularity of the rate-determining step?
(iii) What is the order if the reaction?
2. The reaction mechanism for a reaction is as follows.
Step 1 (slow): O3(g) + NO3(g) → NO3(g) + O2(g)
Step 2 (fast): NO3(g) + NO2(g) → N2O5(g)
(i) Write the overall reaction.
(ii) Identify the molecularity of each step.
(iii) Identify the reactants, products, catalysts and reaction intermediates (whichever apply).
(iv) What is the rate law expression for this mechanism?
3. The reaction mechanism for a reaction is as follows.
Step 1 (slow): Cl(g) + O3(g) → ClO(g) + O2(g)
Step 2 (fast): ClO(g) + O2 → Cl(g) + O2(g)
(i) Write the overall reaction.
(ii) Identify the molecularity of each step.
(iii) Identify the reactants, products, catalysts and reaction intermediates (whichever apply)
(iv) What is the rate law expression for this mechanism?
4. The reaction mechanism for a reaction is as follows.
Step 1 (slow): 2NO(g) + O2(g) → 2NO2(g)
Step 2 (fast): 2[NO2(g) + SO2(g) → NO(g) + SO3(g)]
(i) What is the overall reaction?
(ii) Identify the molecularity of each step.
(iii) Identify the reactants, products, catalysts and reaction intermediates(whichever apply).
(iv) What is the rate law expression for this mechanism?
5. The reaction mechanism for a reaction is as follows.
Step 1 (fast eq.): 2NO(g) → N2O2(g)
Step 2 (fast eq.): N2O2(g) + H2(g) → N2O(g) + H2O(g)
Step 3 (slow): N20(g) + H2(g) → N2(g) + H2
(i) What is the overall reaction?
(ii) Identify the molecularity of each step.
(iii) Identify the reactants, products, catalysts and reaction intermediates
(iv) What is the rate law expression?
6. The reaction for a mechanism is as follows.
Step 1 (fast eq.): I2(g) → 2I(g)
Step 2 (fast eq.): H2(g) + I(g) → H2I(g)
Step 3 (slow): H2I(g) + I(g) → 2HI(g)
(i) What is the overall reaction?
(ii) Identify the molecularity of each step.
(iii) Identify the reactants, products, catalysts and reaction intermediates
(iv) What is the rate law expression?
7. In acidic solution, the breakdown of sucrose into glucose and fructose has the rate law:
rate = k[H+] [sucrose]. The initial rate of sucrose breakdown is measured in a solution that is 0.010 M H+, 0.10 M fructose, and 0.01 M glucose. How does the rate change if
rate = k[H+] [sucrose]. The initial rate of sucrose breakdown is measured in a solution that is 0.010 M H+, 0.10 M fructose, and 0.01 M glucose. How does the rate change if
(a) The concentration of sucrose is changed to 2.5 M?
(b) The concentrations of sucrose, fructose, and glucose are all changed to 0.50 M?
(c) The concentration of H+ is changed to 0.00010 M?
(d) The concentration of sucrose and H+are each changed to 0.10 M?
8. The following data were obtained in the study of a first-order reaction for the decomposition of A to form products.
| [A](M) | 1.00 | 0.80 | 0.60 | 0.35 | 0.15 |
| Time(sec) | 0 | 110 | 255 | 525 | 950 |
(a) What you must plot to show that this reaction follows first-order kinetics?
(b) If a suitable plot is made using given data and a straight line with
slope = -2.0x10-3 is obtained, what are the value and unit of k for this reaction?
slope = -2.0x10-3 is obtained, what are the value and unit of k for this reaction?
9. In order to determine the order of the reaction A + B → C, a student determined the rates at different initial concentrations. His / Her data are tabulated below. Comment on his / her effort.
[A] (mol/L) | [B] (mol/L) | Rate of formation of C (mol/L s) |
0.03 | 0.03 | 3x10-5 |
0.06 | 0.06 | 1.2x10-4 |
0.09 | 0.09 | 2.7x10-4 |
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