CBSE Class 12 Chemistry Chemical Kinetics Worksheet

Question. For the reaction:-
N_2(g) + 3H_2(g) → 2NH_3(g) Under certain conditions of temperature and partial pressure of the reactants, the rate of formation of NH₃ is 10^–3 kg hr^–1. The rate of consumption of H₂ under same condition is:
a. 1.5 × 10^–3 kg hr^–1
b. 6.67 × 10^–4 kg hr^–1
c. 0.0001764 kg hr^–1
d. None of the options

Answer: C

Question. The reaction : A_(g) + 2B_(g) → C_(g) + D_(g) is an elementary process. In an experiment, the initial partial pressure of A and B are P_A = 0.60 atm and PB = 0.80 atm. When P_B = 0.20 atm, the rate of reaction relative to the initial rate is:
a. 1/16
b. 1/24
c. 1/32
d. 1/48

Answer: C

Question. The rate constant of a reaction at 27°C is 2.3 × 10^–3 min^–1 and at this temperature 0.001% of reactant molecules are able to cross the energy barrier existing between the reactants and the products. What is the maximum value of rate constant that can be achieved on raising the temperature?
a. 750 min^–1
b. 230 min^–1
c. 125 min^–1
d. 500 min^–1

Answer: B

Question. The rate of a Ist order reaction is 0.04 mol ltr–1 sec^–1 at 10 seconds and 0.03 mol ltr^–1 sec^–1 at 20 seconds after initiation of reaction. What is t_1/2 of the reaction?
a. 48.2 sec
b. 24.1 sec
c. 37 sec
d. 96 sec

Answer: B

Question. Decomposition of H₂O₂ follows a first order reaction. In fifty minutes, the concentration of H₂O₂ decreases from 0.5 to 0.125 M in one such decomposition. When the concentration of H₂O₂ reaches 0.05 M, the rate of formation of O₂ will be:
a. 2.66 L min^–1 at STP
b. 1.34 × 10_–2 mol min^–1
c. 6.93 × 10^–2 mol min^–1
d. 6.93 × 10^–4 mol min^–1

Answer: C

Question. Two reactions R₁ & R₂ have identical pre-exponential factors. Activation energy of R₁ exceeds that of R₂ by 10 kJ mol^–1. If k1 & k₂ are the rate constants for reactions R₁ & R₂ respectively at 300 K, then ln (k₂/k₁) is equal to: (R = 8.314 J mol–1 k^–1)
a. 12
b.6
c. 4
d. 8

Answer: C

Question. For the equilibrium, A_(g) ⇄ B(_g); ΔH = –40kJ/mol. It the ratio of activation energies of the forward (E_f) & the backward reaction (E_b) is 2 : 3, then:
a. E_f = 30kJ/mol, Eb = 70 kJ/mol
b. E_f = 80kJ/mol, Eb = 120 kJ/mol
c. E_f = 60kJ/mol, E_b = 100 kJ/mol
d. None of these

Answer: B

Question. Hydrogenation of vegetable ghee at 25°C reduces pressure of H₂ from 2 atm to 1.2 atm in 50 minute. The rate of reaction in terms of molarity per second is -
a. 1.09 × 10^–6
b. 1.09 × 10^–5
c. 1.09 × 10^–7
d. 1.09 × 10^–9

Answer: B

Question. In a reaction A₂B₃ (g) → A₂ (g) + 3/2 B₂ (g), the pressure changes from 60 torr to 75 torr in 2.5 minutes. The rate of disappearance of A₂B₃ is -
a. 8 torr min^–1
b. 18 torr min^–1
c. 4 torr min^–1
d. 10 torr min^–1

Answer: C

Question. The ratio t7/8 : t1/2 for the first order reaction is -
a. 3
b. 5
c. 2
d. 7

Answer: A

Question. Which of the following statement are correct -
a. In an Arrehenius equation K = Ae^–Ea/RT, if T → ∞ K = A
b. Alkaline hydrolysis of ester is irreversible reaction
c. Rate of reaction increase with increase in temperature
d. All of these

Answer: A

Question. Half life (t_1/2) and completion time (T) of the zero order reaction are- (K = 0.001 mol/litre / sec and a = 1 M.)
a. 500 min, 750 min
b. 500 sec, 750 sec
c. 500 sec, 1000 sec
d. None of the options

Answer: C

Question. A reaction obeys zero order. The time required to decompose 50 g out of 100 g of the reactant A is 10 minute. Calculate the time required when half of the reactant A is decomposed if its initial mass is 200 g :
a. 5
b. 10
c. 15
d. 20

Answer: D

Question. The activation energy for a reaction is 9.0 kcal/mol.
The increase in the rate constant when its temperature is increased from 298 K to 308 K is -
a. 10 %
b. 100 %
c. 50 %
d. 63 %

Answer: D

Question. For a first order reaction, more than one option are correct
a. The degree of dissociation is equal to (1–e^–Kt)
b. The time taken for the completion of 75% reaction is thrice the t_1/2 of the reaction
c. The pre-exponential factor in the Arrhenius equation has the dimension of time, (T^–1)
d. Both (a) & (c)

Answer: A, D

Question.  Two first order reaction have half-lives in the ratio 8 : 1. Calculate the ratio of time intervals t₁ : t₂. The time t₁ and t₂ are the time period for (1/4) and (3/4) completion
a. 1 : 0.301
b. 0.125 : 0.602
c. 1 : 602
d. None of the options

Answer: C

Question. The rate constant is numerically the same for three reactions of first, second and third order respectively. Which of the following is correct ?
a. If [A] = 1 then r1 = r2 = r3
b. If [A] < 1 then r1 > r2 > r3
c. If [A] > 1 then r3 > r2 > r1
d. All of the options

Answer: D

Question. In the formation of HBr from H₂ & Br₂, following mechanism is observed.
1. Br₂ ⇄ 2Br^• Equilibrium step 
2. H₂ + Br• → HBr + H^• Slow step
3. H^• + Br² → HBr +Br^• Fast step
Calculate the rate of reaction, if concentration of hydrogen is twice that of bromine and the rate constant is equal to 1 M^–1/2 Sec^–1. Concentration of bromine is 1 M.
a. 2 M Sec^–1
b. 3 M Sec^–1
c. 4 M Sec^–1
d. 5 M Sec^–1

Answer: A

Question. The reaction A_(g) + 2B_(g) → C_(g) + D_(g) is an elementary process. In an experiment, the initial pressures of A & B are P_A = 0.60 & P_B = 0.80 atm. When P_C = 0.2 atm, the rate of reaction relative to initial rate is
a. 1/40
b. 1/24
c. 9/16
d. 1/6

Answer: D

Question. For a reaction occuring at 500 k, activation energy is found to be 1000 X Jmol^–1. The value of boltzmann factor (b) is given by:
a. logb = 2x/2.303R
b. log b = 2000x/2.303R
c. log b = 2x/R
d. log b = 2x/2.303R

Answer: A

Question. Half life of first orders reaction and half life of 2^nd order reaction are equal. Hence the ratio of their rates at the start of the reaction is/are
a. 1
b. 2
c. 0.693
d. 1.44

Answer: C

Question. In presence of a catalyst, the activation energy is lowered by 2 kcal at 127°C. The rate as compared to old rate is
a. e² times
b. e^–2 times
c. e^2.5 times
d. e^–4.5 times

Answer: C

Question. Consider the reaction 2A + B → Product. When concentration of B alone was doubled, the half life did not change. When concentration of A alone was doubled, the rate increased by two times. The unit of rate constant for this reaction is
a. s^–1
b. L mol^–1s^–1
c. L mol²s^–1
d. mol L^–1 s^–1

Answer: B

Question. The time required for 10% completion of a first order reaction at 298 k is equal to that required for its 25% completion at 308. If the value of A is 4 × 10¹⁰ s^–1. The value of E_a is (log 2.728 = 0.436)
a. 76.623 kJ/mol
b. 100 kJ/mol
c. 94 kJ/mol
d. 52.261 kJ/mol

Answer: A

Question. The order of a reaction A → product in which half the reagent is reacted in half an hour, three quarters in one hour and seven - eighth in one and half hours is
a. 2
b. 1
c. Zero
d. –1

Answer: B

Question. Assign T/F to the following statements.
1 : The frequency factor has the same unit as the rate constant k
2 : A plot ln C for the nth order reaction gives a straight line with slope -n and intercept kn
3 : The order of a reaction A → product in which half the reagent is reacted in half an hour, three quarters in one hour and seven - eighth in one and half hours must be 1 (unity).
4 : The unit of rate constant for a second order reaction will be M^–1s^–1. (M is representing the molarity of solution)
a. T F T T
b. T T T T
c. F F T T
d. T F F T

Answer: A

Question. A 0.5 L reaction vessel which is equipped with a movable piston is filled completely with a 1 M aqueous solution of H₂O₂. The H₂O₂ decomposes to H₂O and O₂ (g) in a first order process with half life of 10 hrs at 300 k. As H₂O₂ decomposes, the piston moves up against constant external pressure of 1 atm. The net work done from the start of sixth hour till the end of 10 hours is nearlya.
–100 J
b. –120 J
c. –130 J
d. –150 J

Answer: C

Question. Tn the initial concentration is 0.3 mol L^–1. The rate constant ishe rate of a first order reaction is 1.8 × 10^–3 mol L^–1 min^–1 whe
a. 1 × 10^–2 s^–1
b. 1 × 10^–4 s^–1
c. 6 × 10^–2 s^–1
d. 4 × 10^–4 s^–1

Answer: B

Question. The rate law for a reaction between the substances A and B is given by rate = k[A]ⁿ[B]^m. On doubling the concentration of A and halving the concentration of B, the ratio of the new rate to the earlier rate of reaction will be
a. 1/2^{(m n)}
b. m + n
c. n – m
d. 2^{(n – m)}

Answer: D

Question. If the rate of a reaction at 50 °C is 2.6 × 10^–3 mol L^–1 s^–1, then what will be rate of reaction at 80 °C? (Given that the temperature coefficient is 3.)
a. 7.02 × 10^–2
b. 7.025 × 10^–3
c. 7.8 × 10^–3
d. None of the options

Answer: A

Question. The Arrhenius equation k = Ae E_a/RT − = shows the dependence of rate constant on temperature. In which condition the rate constant k is smallest for a reaction?
a. Small E_a and low T
b. Small E_a and high T
c. Large E_a and low T
d. Large E_a and high T

Answer: C

40. For two reactions, A → Products & B → Products have rate constants K_A & K_B at temperature. T & activation energies E_A & E_B respectively. If K_A > K_B & E_A < E_B & assuming that A for both the reactions is same, then
a. At higher temperatures K_A will be greater than K_B
b. At lower temperature, K_A & K_B will differ more & K_A > K_B
c. As temperature rises, K_A & K_B will be close to each other in magnitude.
d. All of the above are correct

Answer: D

 

VERY - SHORT - ANSWER QUESTION

1. Define the term rate of reaction.

2. Define the term ‘Rate Constant’.

3. What is meant by half life period for zero order?

4. Write an expression for the half life period of a first order reaction.

5. Write the definition of instantaneous rate of reaction.

6. What is Boltzmann factor?

7. What are the factors which affect the rate of a reaction?

8. When could order and molecularity of a reaction be same?

9. After five half-life period for a first order reaction what fraction of reaction remains.

10. How much percentage of average kinetic energy increase when temperature increase by 10 K?

11. what is a complex reaction?

12. Write the relationship between rate constant and activation energy of a reaction.

13. When does the averge rate of reaction become equal to instantaneous rate?

14. Why diamond does not change into graphite for years, although graphite the more stable than diamond. Why?

15. Some times the colliding molecule have energy more than threshold energy but still the reaction does not occur. Why?

16. Give the relationship between the half life period of a reaction and its initial concentration for a reaction of nth order.

17. What is meant by half life period for a reaction?

18. Among the elementary processes, in the proposed mechanism of reaction, which is rate-determining step?

19. Give one example of the reaction having fractional value of order.

20. Mention one example of zero order reaction.

21. In which order of reaction, rate of reaction become equal to specific reaction rate?

22. The reaction A + B  →  2C obeys rate equation : Rate = k[A]^1/2 [B]^3/2 . What is overall order of reation?

23. The reactionA + B  →  C has zero order. Write rate equation.

24. Give units of specific rate constant for a zero order reaction.

25. Rate constant for a reaction is 1.85 × 10² s^–1. Give the order of reaction.

 

SHORT - ANSWER - QUESTIONS

1. Write units of rate constant for the following reactions, if concentration is expressed in molarity and time in seconds: (i) Zero order reaction, (ii) First order reaction.

2. What is meant by a pseudo first order reaction? Write one example.

3. Is rate constant in zero order depend on the initial concentration?

4. Write the difference between molecularity and order of reaction?

5. For expresion t_1/2 =1/[A_º ]  , what is order of reaction?

6. For the reaction 2 2 3 N (g) 3H (g)2NH (g) , express the order of reaction, when concentration is

(i) low (ii) high.

7. Give two points of difference between reaction rate and reaction constant?

8. What is temperature coefficient?

9. How is rate of reaction related to concentration of the reactants?

10. What is the effect of concentration on the decomposition of NH3 regarding order of reaction?

11. What are pseudo uni-molecular reactions? Give two examples.

12. List the factors which affect the rate of reaction.

13. List two differences between rate of reaction and reaction rate constant.

14. What is difference between the average rate and instantaneous rate of a chemical reaction.?

15. How a catalyst increases the rate of reaction?

 

LONG - ANSWER - QUESTIONS

1. List two methods that can be used to determine the order of a reaction. Discuss one of them.

2. Derive the equation for rate constant of a first order reaction.

3. Explain the collision theory.

4. Define activation energy and explain the temperature dependence of the reaction rate on its basis.

5. State the role of activated complex in a relation and state its relation with activation energy.

6. Derive an expression for the rate constant and half life period of a zero order reaction.

7. On what factor does the potential energy of the interacting molecules depend as per the transition state theory of mechanism of reaction be same?

8. How will you find order of a reaction by Ostwald isolation method?

9. Define the following

(i) Rate law, (ii) Threshold energy, (iii) Activation energy

10. How will you determine the order of a reaction by integrated rate law method? Give the significance of integrated rate equation.

 

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