chemistry class 12 english capter 3
1. From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.
(i) 3NO(g) → N₂O (g) Rate = k [NO]²
(ii) H₂O₂ (aq) + 3I⁻ (aq)+ 2H⁺ → 2H₂O (l) +I⁻₃ Rate = k [H₂O₂][I⁻]
(iii) CH3CHO (g) → CH₄ (g) + CO(g) Rate = k [CH3CHO]³/²
(iv) C₂H₅Cl (g) → C₂H₄ (g) + HCl (g) Rate = k [C₂H₅Cl]
2. For the reaction:
2A + B → A₂B
the rate = k[A][B]² with k = 2.0 × 10⁻⁶ mol⁻² L² s⁻¹ . Calculate the initial rate of the reaction when [A] = 0.1 mol L⁻¹ , [B] = 0.2 mol L⁻¹ . Calculate the rate of reaction after [A] is reduced to 0.06 mol L⁻¹ .
3. The decomposition of NH3 on platinum surface is zero order reaction. What are the rates of production of N₂ and H₂ if k = 2.5 × 10⁻⁴ mol⁻¹ L s ⁻¹?
4. The decomposition of dimethyl ether leads to the formation of CH₄ , H₂ and CO and the reaction rate is given by
Rate = k [CH₃OCH₃ ] ³/²
The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether, i.e.,
k [CH3OCH3]³/²
If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constants?
5. Mention the factors that affect the rate of a chemical reaction.
6. A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is
(i) doubled (ii) reduced to half ?
7. What is the effect of temperature on the rate constant of a reaction? How can this effect of temperature on rate constant be represented quantitatively?
8. In a pseudo first order reaction in water, the following results were obtained:
t/s 0 30 60 90
[A]/mol L⁻¹ 0.55 0.31 0.17 0.085
9. A reaction is first order in A and second order in B.
(i) Write the differential rate equation.
(ii) How is the rate affected on increasing the concentration of B three times?
(iii) How is the rate affected when the concentrations of both A and B are doubled?
10. In a reaction between A and B, the initial rate of reaction (r₀ ) was measured for different initial concentrations of A and B as given below:
A/mol L⁻¹ 0.20 0.20 0.40
b/mol L⁻¹ 0.30 0.10 0.05
r₀/mol L⁻¹s⁻¹ 5.07 x 10⁻⁵ 5.07 x 10⁻⁵ 1.43 x 10⁻⁴
11. The following results have been obtained during the kinetic studies of the reaction:
2A + B → C + D
| Experimen | A/mol L⁻¹ | B/mol L⁻¹ | Initial rate of formation of D/mol L⁻¹ min⁻¹ |
I. | 0.1 | 0.1 | 6.0 x 10⁻³ |
II. 2. | 0.3 | 0.2 | 7.2 x 10⁻² |
III. | 0.3 | 0.4 | 2.88 x 10⁻¹ |
IV. | 0.4 | 0.1 | 2.40 x 10⁻² |
Determine the rate law and the rate constant for the reaction.
12. The reaction between A and B is first order with respect to A and zero order with respect to B. Fill in the blanks in the following table:
Experimen | [A]/ mol L⁻¹ | [B]/ mol L⁻¹ | Initial rate/mol L⁻¹ min⁻¹ |
i. | 0.1 | 0.1 | 2.0 x 10⁻² |
ii. | - | 0.2 | 4.0 x 10⁻² |
iii. | 0.4 | 0.4 | - |
iv. | - | 0.2 | 2.0 x 10⁻² |
13. Calculate the half-life of a first order reaction from their rate constants given below:
(i) 200 s⁻¹(ii) 2 min⁻¹ (iii) 4 year⁻¹
14. The half-life for radioactive decay of ¹⁴C is 5730 years. An archaeological artifact containing wood had only 80% of the ¹⁴C found in a living tree. Estimate the age of the sample.
15. The experimental data for decomposition of N₂O₅
[2 N2O₅ → 4NO₂ + O₂]
t/s | 0 | 400 | 800 | 1200 | 1600 | 2000 | 2400 | 2800 | 3200 |
10² x [N₂O₅]/mol L⁻¹ | 1.63 | 1.36 | 1.14 | 0.93 | 0.78 | 0.64 | 0.53 | 0.43 | 0.35 |
(i) Plot [N₂O₅ ] against t. (ii) Find the half-life period for the reaction.
(iii) Draw a graph between log[N₂O₅] and t.
(iv) What is the rate law ? Reprint 2024-25 87 Chemical Kinetics
(v) Calculate the rate constant.
(vi) Calculate the half-life period from k and compare it with (ii).
16. The rate constant for a first order reaction is 60 s⁻¹. How much time will it take to reduce the initial concentration of the reactant to its 1/16th value?
17. During nuclear explosion, one of the products is ⁹⁰Sr with half-life of 28.1 years. If 1mg of ⁹⁰Sr was absorbed in the bones of a newly born baby instead of calcium, how much of it will remain after 10 years and 60 years if it is not lost metabolically.
18. For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.
19. A first order reaction takes 40 min for 30% decomposition. Calculate t¹/² .
20. For the decomposition of azoisopropane to hexane and nitrogen at 543 K, the following data are obtained.
t(sec) | P(mm Hg esa ) |
0 | 35.0 |
360 | 54.0 |
720 | 63.0 |
Calculate the rate constant.
21. The following data were obtained during the first order thermal decomposition of SO₂Cl₂ at a constant volume.
SO₂ Cl₂ (g) SO₂ (g) Cl₂ (g)
Experiment | Time/s–1 | Total pressure/atm |
1 | 0 | 0.5 |
2 | 100 | 0.6 |
Calculate the rate of the reaction when total pressure is 0.65 atm.
22. The rate constant for the decomposition of N₂O₅ at various temperatures is given below:
T/°C | 0 | 20 | 40 | 60 | 80 |
10⁵ X K/S⁻¹ | 0.0787 | 1.70 | 25.7 | 178 | 2140 |
Draw a graph between ln k and 1/T and calculate the values of A and Eₐ . Predict the rate constant at 30° and 50°C.
23. The rate constant for the decomposition of hydrocarbons is 2.418 × 10⁻⁵ s⁻¹ at 546 K. If the energy of activation is 179.9 kJ/mol, what will be the value of pre-exponential factor.
24. Consider a certain reaction A → Products with k = 2.0 × 10 ⁻²s ⁻¹. Calculate the concentration of A remaining after 100 s if the initial concentration of A is 1.0 mol L⁻¹ .
25. Sucrose decomposes in acid solution into glucose and fructose according to the first order rate law, with t₁/₂ = 3.00 hours. What fraction of sample of sucrose remains after 8 hours ?
26. The decomposition of hydrocarbon follows the equation
k = (4.5 × 10¹¹s⁻¹) e⁻²⁸⁰⁰⁰K/T
Calculate Eₐ .
27. The rate constant for the first order decomposition of H₂O₂ is given by the following equation: log k = 14.34 – 1.25 × 10⁴K/T Calculate Eₐ for this reaction and at what temperature will its half-period be 256 minutes?
28. The decomposition of A into product has value of k as 4.5 × 10³ s⁻¹ at 10°C and energy of activation 60 kJ mol⁻¹. At what temperature would k be 1.5 × 10⁴s ⁻¹?
29. The time required for 10% completion of a first order reaction at 298K is equal to that required for its 25% completion at 308K. If the value of A is 4 × 10¹⁰s ⁻¹. Calculate k at 318K and Eₐ .
30. The rate of a reaction quadruples when the temperature changes from 293 K to 313 K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.
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