Chemical Kinetics

Previous Years' CBSE Board Questions

3.1 Rate of a Chemical Reaction

SAL (2 marks)

1. In the given reaction, <math>N_{2(g)} + 3H_{2(g)} \longrightarrow 2NH_{3(g)}</math> the rate of formation of NH3 is 3.6 ×10^-4 mol L^-1 s^-1. Calculate the
2. rate of reaction and
3. rate of disappearance of H_2(g). (Term-II, 2021-22) (Ap)

1. The following reaction was carried out in water: <math>Br_2 + 2l^- \longrightarrow 2Br^- + l_2</math> The initial concentration of I" was 0.30 M and the concentration after 10 minutes reduced to 0.28 M. Calculate the ratio of disappearance of I and production of l2. (2021 C)

1. In the given reaction, A + 3B <math>\rightarrow</math> 2C, the rate of formation of C is <math>2.5 \times 10^{-4}</math> mol L^-1 s^-1. Calculate the
2. rate of reaction, and
3. rate of disappearance of B. (2020)

1. For the reaction, <math>2N_2O_{5(g)} \rightarrow 4NO_{2(g)} + O_{2(g)}</math>, the rate of formation of <math>NO_{2(g)}</math> is <math>2.8 \times 10^{-3}</math> M s^-1. Calculate

the rate of disappearance of <math>N_2O_{5(g)}</math>. (2018)

3.2 Factors Influencing Rate of a Reaction

MCQ

1. The following experimental rate data were obtained for a reaction carried out at 25°C:

<math>A_{(g)} + B_{(g)} \rightarrow C_{(g)} + D_{(g)}</math>

Initial [A_(r)] / Initial [B(g)]/ Initial rate/ mol dm^-3 mol dm^-3 mol dm-3 s-1 <math>3.0 \times 10^{-2}</math> <math>2.0 \times 10^{-2}</math> <math>1.89 \times 10^{-4}</math> <math>3.0 \times 10^{-2}</math> <math>4.0 \times 10^{-2}</math> <math>1.89 \times 10^{-4}</math> <math>6.0 \times 10^{-2}</math> <math>4.0 \times 10^{-2}</math> <math>7.56 \times 10^{-4}</math>

What are the orders with respect to <math>A_{(g)}</math> and <math>B_{(g)}</math>?

Assertion (A): The molecularity of the reaction

<math>H_2 + Br_2 \longrightarrow 2HBr</math> appears to be 2.

Reason (R): Two molecules of the reactants are

involved in the given elementary reaction.

1. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is true, but Reason (R) is false.

Assertion (A) is false, but Reason (R) is true.

(2023)

1. Assertion: Order of reaction is applicable to elementary as well as complex reactions. Reason: For a complex reaction molecularity has no meaning.
2. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A)
3. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A)
4. Assertion (A) is true, but Reason (R) is false.
5. Assertion (A) is false, but Reason (R) is true.

(2023)

Assertion (A): The molecularity of the reaction

<math>H_2 + Br_2 \rightarrow 2HBr</math> appears to be 2.

Reason (R): Two molecules of the reactants are

involved in the given elementary reaction.

1. Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A).
2. Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A).
3. Assertion (A) is correct, but Reason (R) is incorrect statement.
4. Assertion (A) is incorrect, but Reason (R) is correct statement. (2020)

VSA (1 mark)

Calculate the overall order of the reaction whose

rate law expression was predicted as:

Order with Order with respect to A(g) respect to B(g)

1. Zero Second
2. First Zero
3. Second Zero
4. Second First

Rate = <math>k[NO]^{3/2}[O_2]^{1/2}</math>.

(2020) U

Define the rate constant.

(1/5, Foreign 2015, Delhi 2015C)

(2023)

Define the specific rate of reaction. (Al 2014C) R

SAI (2 marks)

12 Define rate of reaction. Write two factors that affect the rate of reaction. (Term-II, 2021-22, AI 2015)

1. Write two differences between 'order of reaction' and 'molecularity of reaction'.

(Term-II, 2021-22C, Delhi 2014)

For a reaction

(2020)

2H₂O₂ F 2H₂O+O₂

the proposed mechanism is as given below:

H₂O₂ + Γ → H₂O + IO^- (slow)

1. H₂O₂ + IO^- → H₂O + I^- + O₂ (fast)
2. Write rate law for the reaction.
3. Write the overall order of reaction.

Experiment [A]/M [B]/M Initial rate of formation

of C/M min^-1

1 0.2 0.3 <math>4.2 \times 10^{-2}</math>

2 0.1 0.1 <math>6.0 \times 10^{-3}</math>

3 0.4 0.3 <math>1.68 \times 10^{-1}</math>

4 0.1 0.4 <math>2.40 \times 10^{-2}</math>

1. Out of steps (1) and (2), which one is rate determining step? (Delhi 2019) Ap
2. For a reaction: <math>2NH_{3(g)} \xrightarrow{Pt} N_{2(g)} + 3H_{2(g)}</math>;

Rate = k

1. Write the order and molecularity of this reaction.
2. Write the unit of k. (Delhi 2016)

For a reaction: H₂ + Cl₂ hu → 2HCl; Rate = k

1. Write the order and molecularity of this reaction
2. Write the unit of k. (Al 2016)

For a reaction A + B → P, the rate is given by Rate = <math>k[A][B]^2</math>

1. How is the rate of reaction affected if the concentration of B is doubled?
2. What is the overall order of reaction if A is present in large excess? (2/5, Delhi 2015)

Write units of rate constants for zero order and for the second order reactions if the concentration is expressed in mol L^-1 and time in second. (Al 2015C)

1. 2 (2023)
2. (i) For a reaction, <math>A + B \rightarrow Product</math>, the rate law is given by, Rate = <math>k[A]^{1}[B]^{2}</math>. What is the order of the reaction?
3. Write the unit of rate constant 'k' for the first order reaction. (Delhi 2014C) [U]

A reaction is of second order with respect to its reactant. How will its reaction rate be affected if the concentration of the reactant is (i) doubled

1. reduced to half? (Al 2014C)

Assertion (A): Hydrolysis of an ester follows first

order kinetics.

SA II (3 marks)

1. Following data were obtained for the given reaction: <math>X + Y \longrightarrow Product</math>
2. Find the order of reaction with respect to X and Y.
3. Write the rate law expression.
4. Find the rate constant. (2021C) EV
5. How will the rate of the reaction be affected when
6. surface area of the reactant is reduced.
7. catalyst is added in a reversible reaction, and
8. temperature of the reaction is increased?
9. The following data were obtained for the reaction: <math>A + 2B \longrightarrow C</math>
10. Find the order of reaction with respect to A and B.
11. Write the rate law and overall order of reaction.
12. Calculate the rate constant (k). (2019) An

A reaction is second order in A and first order in B.

1. Write the differential rate equation.
2. How is the rate affected on increasing the concentration of A three times?
3. How is the rate affected when the concentration of both A and B are doubled? (2018 C)

3.3 Integrated Rate Equations

MCQ

The order of the reaction

<math>H_{2(g)} + Cl_{2(g)} \xrightarrow{hv} 2HCl_{(g)}</math> is<br>

(b) 1 (c) 0 (d) 3

The half-life period for a zero order reaction is equal to

(a) <math>\frac{0.693}{k}</math> (b) <math>\frac{2k}{[R]_0}</math> (c) <math>\frac{2.303}{k}</math> (d)

(where <math>[R]_0</math> is initial concentration of reactant and k

is rate constant.) (2020) An

Reason (R): Concentration of water remains nearly

constant during the course of the reaction.

(a) Both Assertion (A) and Reason (R) are correct

statements, and Reason (R) is the correct

explanation of the Assertion (A).

Exp. [X]/M [Y]/M Initial Rate M min-1 1 0.1 M 0.2 M 0.05 2 0.2 M 0.2 M 0.10 3 0.1 M 0.1 M 0.05 (b)