CBSE Class 12 Chemistry Chemical Kinetics Question Bank Set A

Question. For the reaction N₂O_5(g) → 2NO_2(g) + 1/2O_2(g) the value of rate of disappearance of N2O5 is given as 6.25 × 10^–3 mol L^–1s^–1. The rate of formation of NO₂ and O₂ is given respectively as :
(a) 6.25 × 10^–3 mol L^–1 s^–1 and 6.25 × 10^–3 mol L^–1 s^–1
(b) 1.25 × 10^–2 mol L^–1 s^–1 and 3.125 × 10^–3 mol L^–1 s^–1
(c) 6.25 × 10^–3 mol L^–1 s^–11 and 3.125 × 10^–3 mol L^–1 s^–1
(d) 1.25 × 10^–2 mol L^–1 s^–1 and 6.25 × 10^–3 mol L^–1 s^–1
Answer. B

Question. Mechanism of a hypothetical reaction,
X₂ + Y₂ → 2XY, is given below :
(i) X₂  → X + X (fast)
(ii) X + Y₂  →  XY + Y (slow)
(iii) X + Y  → XY (fast)
The overall order of the reaction will be
(a) 2
(b) 0
(c) 1.5
(d) 1 
Answer. C

Question. The decomposition of phosphine (PH₃) on tungsten at low pressure is a first-order reaction. It is because the
(a) rate is proportional to the surface coverage
(b) rate is inversely proportional to the surface coverage
(c) rate is independent of the surface coverage
(d) rate of decomposition is very slow
Answer. A

Question. The rate constant of the reaction A B is 0.6 × 10^–3 mol L^–1 s^–1. If the concentration of A is 5 M, then concentration of B after 20 minutes is
(a) 3.60 M
(b) 0.36 M
(c) 0.72 M
(d) 1.08 M 
Answer. C

Question. For a reaction between A and B the order with respect to A is 2 and the order with respect to B is 3.The concentrations of both A and B are doubled, the rate will increase by a factor of
(a) 12
(b) 16
(c) 32
(d) 10
Answer. C

Question. In a reaction, A + B → product, rate is doubled when the concentration of B is doubled, and rate increases by a factor of 8 when the concentration of both the reactants (A and B) are doubled, rate law for the reaction can be written as
(a) rate = k[A][B]²
(b) rate = k[A]²[B]²
(c) rate = k[A][B]
(d) rate = k[A]²[B]
Answer. D

Question. Which one of the following statements for the order of a reaction is incorrect?
(a) Order can be determined only experimentally.
(b) Order is not influenced by stoichiometric coefficient of the reactants.
(c) Order of a reaction is sum of power to the concentration terms of reactants to express the rate of reaction.
(d) Order of reaction is always whole number.
Answer. D

Question. The unit of rate constant for a zero order reaction is
(a) mol L^–1 s^–1
(b) L mol^–1 s^–1
(c) L² mol^–2 s^–1
(d) s^–1
Answer. A

Question. For the reaction, A + B → products, it is observed that
(i) on doubling the initial concentration of A only, the rate of reaction is also doubled and
(ii) on doubling the initial concentration of both A and B, there is a change by a factor of 8 in the rate of the reaction.
The rate of this reaction is given by
(a) rate = k[A][B]²
(b) rate = k[A]²[B]²
(c) rate = k[A][B]
(d) rate = k[A]²[B]
Answer. A

Question. The reaction of hydrogen and iodine monochloride is given as :
H_2(g) + 2ICl(g) → 2HCl_(g) + I_2(g)
This reaction is of first order with respect to H_2(g) and ICl_(g), following mechanisms were proposed.
Mechanism A :
H_2(g) + 2ICl_(g) → 2HCl_(g) + I_2(g)
Mechanism B :
H_2(g) + ICl_(g) → HCl_(g) + HI_(g) ; slow
HI_(g) + ICl_(g) → HCl_(g)) + I_2(g) ; fast
Which of the above mechanism(s) can be consistent with the given information about the reaction?
(a) A and B both
(b) Neither A nor B
(c) A only
(d) B only
Answer. D

Question. The rate of reaction between two reactants A and B decreases by a factor of 4 if the concentration of reactant B is doubled. The order of this reaction with respect to reactant B is
(a) 2
(b) –2
(c) 1
(d) –1 
Answer. B

Question. If the rate of the reaction is equal to the rate constant, the order of the reaction is
(a) 0
(b) 1
(c) 2
(d) 3 
Answer. A

Question. 2A → B + C, It would be a zero order reaction when
(a) the rate of reaction is proportional to square of concentration of A
(b) the rate of reaction remains same at any concentration of A
(c) the rate remains unchanged at any concentration of B and C
(d) the rate of reaction doubles if concentration of B is increased to double.
Answer. B

Question. For the reaction; 2N₂O₅ → 4NO₂ + O₂ rate and rate constant are 1.02 × 10^–4 and 3.4 × 10^–5 sec^–1 respectively, then concentration of N₂O₅ at that time will be
(a) 1.732
(b) 3
(c) 1.02 × 10^–4
(d) 3.4 × 10⁵
Answer. B

Question. The given reaction, 2FeCl₃ + SnCl₂ → 2FeCl₂ + SnCl₄ is an example of
(a) third order reaction
(b) first order reaction
(c) second order reaction
(d) none of these. 
Answer. A

Question. The data for the reaction A + B → C, is
Exp.   [A]₀       [B]₀      Initial rate
1      0.012      0.035      0.10
2      0.024      0.070      0.80
3      0.024      0.035      0.10
4      0.012      0.070      0.80
The rate law corresponds to the above data is
(a) rate = k[A][B]³
(b) rate = k[A]²[B]²
(c) rate = k[B]³
(d) rate = k[B]⁴.
Answer. C

Question. The rate constant for a first order reaction is 4.606 × 10^–3 s^–1. The time required to reduce 2.0 g of the reactant to 0.2 g is
(a) 100 s
(b) 200 s
(c) 500 s
(d) 1000 s 
Answer. C

Question. If the rate constant for a first order reaction is k, the time (t) required for the completion of 99% of the reaction is given by
(a) t = 2.303/k
(b) t = 0.693/k
(c) t = 6.909/k
(d) t = 4.606/k
Answer. D

Question. A first order reaction has a rate constant of 2.303 × 10^–3 s^–1. The time required for 40 g of this reactant to reduce to 10 g will be [Given that log10 2 = 0.3010]
(a) 230.3 s
(b) 301 s
(c) 2000 s
(d) 602 s
Answer. D

Question. The correct difference between first and second order reactions is that
(a) the rate of a first-order reaction does not depend on reactant concentrations; the rate of a second-order reaction does depend on reactant concentrations
(b) the half-life of a first-order reaction does not depend on [A]₀ ; the half-life of a second-order reaction does depend on [A]₀
(c) a first-order reaction can be catalysed; a secondorder reaction cannot be catalysed
(d) the rate of a first-order reaction does depend on reactant concentrations; the rate of a secondorder reaction does not depend on reactant concentrations. 
Answer. B

Question. When initial concentration of the reactant is doubled, the half-life period of a zero order reaction
(a) is halved
(b) is doubled
(c) is tripled
(d) remains unchanged.
Answer. B

Question. A first order reaction has a specific reaction rate of 10^–2 sec^–1. How much time will it take for 20 g of the reactant to reduce to 5 g?
(a) 138.6 sec
(b) 346.5 sec
(c) 693.0 sec
(d) 238.6 sec 
Answer. A

Question. The rate of first-order reaction is 0.04 mol L^–1 s^–1 at 10 seconds and 0.03 mol L^–1 s^–1 at 20 seconds after initiation of the reaction. The half-life period of the reaction is
(a) 44.1 s
(b) 54.1 s
(c) 24.1 s
(d) 34.1 s 
Answer. C

Question. When initial concentration of a reactant is doubled in a reaction, its half-life period is not affected. The order of the reaction is
(a) second
(b) more than zero but less than first
(c) zero
(d) first. 
Answer. D

Question. A reaction is 50% complete in 2 hours and 75% complete in 4 hours. The order of reaction is
(a) 1
(b) 2
(c) 3
(d) 0
Answer. A

Question. The half-life of a substance in a certain enzymecatalysed reaction is 138 s. The time required for the concentration of the substance to fall from 1.28 mg L^–1 to 0.04 mg L^–1 is
(a) 414 s
(b) 552 s
(c) 690 s
(d) 276 s
Answer. C

Question. Half-life period of a first order reaction is 1386 seconds. The specific rate constant of the reaction is
(a) 0.5 × 10^–2 s^–1
(b) 0.5 × 10^–3 s^–1
(c) 5.0 × 10^–2 s^–1
(d) 5.0 × 10^–3 s^–1
Answer. B

Question. If 60% of a firstorder reaction was completed in 60 minutes, 50% of the same reaction would be completed in approximately (log 4 = 0.60, log 5 = 0.69)
(a) 45 minutes
(b) 60 minutes
(c) 40 minutes
(d) 50 minutes.
Answer. A

Question.For a first order reaction A → B the reaction rate at reactant concentration of 0.01 M is found to be 2.0 × 10^–5 mol L^–1 s^–1. The half-life period of the reaction is
(a) 30 s
(b) 220 s
(c) 300 s
(d) 347 s
Answer. D

Question. The rate of a first order reaction is 1.5 × 10^–2 mol L^–1 min^–1 at 0.5 M concentration of the reactant. The half-life of the reaction is
(a) 0.383 min
(b) 23.1 min
(c) 8.73 min
(d) 7.53 min
Answer. B

Question. The reaction A → B follows first order kinetics. The time taken for 0.8 mole of A to produce 0.6 mole of B is 1 hour. What is the time taken for conversion of 0.9 mole of A to produce 0.675 mole of B ?
(a) 1 hour
(b) 0.5 hour
(c) 0.25 hour
(d) 2 hours
Answer. A

Question. For a first-order reaction, the half-life period is independent of
(a) first power of final concentration
(b) cube root of initial concentration
(c) initial concentration
(d) square root of final concentration
Answer. C

Question. For a reaction, activation energy Ea = 0 and the rate constant at 200 K is 1.6 × 106 s^–1. The rate constant at 400 K will be [Given that gas constant R = 8.314 J K^–1 mol^–1]
(a) 3.2 × 10⁴ s^–1
(b) 1.6 × 10⁶ s^–1
(c) 1.6 × 10³ s^–1
(d) 3.2 × 10⁶ s^–1
Answer. B

Question. The addition of a catalyst during a chemical reaction alters which of the following quantities?
(a) Enthalpy
(b) Activation energy
(c) Entropy
(d) Internal energy
Answer. B

Question. What is the activation energy for a reaction if its rate doubles when the temperature is raised from 20 °C to 35 °C? (R = 8.314 J mol^–1 K^–1)
(a) 34.7 kJ mol^–1
(b) 15.1 kJ mol^–1
(c) 342 kJ mol^–1
(d) 269 kJ mol^–1
Answer. A

Question. In a zero-order reaction, for every 10 °C rise of temperature, the rate is doubled. If the temperature is increased from 10 °C to 100 °C, the rate of the reaction will become
(a) 256 times
(b) 512 times
(c) 64 times
(d) 128 times.
Answer. B

Question. The rate of the reaction,
2NO + Cl₂ → 2NOCl is given by the rate equation, rate = k[NO]₂[Cl₂]. The value of the rate constant can be increased by
(a) increasing the temperature
(b) increasing the concentration of NO
(c) increasing the concentration of the Cl₂
(d) doing all of these.
Answer. A

Question. The activation energy for a simple chemical reaction A ⇔ B is Ea in forward direction. The activation energy for reverse reaction
(a) is negative of E_a
(b) is always less than E_a
(c) can be less than or more than E_a
(d) is always double of E_a. 
Answer. C

Question. When a biochemical reaction is carried out in laboratory, outside the human body in absence of enzyme, then rate of reaction obtained is 10–6 times, the activation energy of reaction in the presence of enzyme is
(a) 6/RT
(b) P is required
(c) different from Ea obtained in laboratory
(d) can’t say anything.
Answer. A

Question. How enzymes increases the rate of reactions?
(a) By lowering activation energy
(b) By increasing activation energy
(c) By changing equilibrium constant
(d) By forming enzyme substrate complex
Answer. A

Question. Activation energy of a chemical reaction can be determined by
(a) evaluating rate constants at two different temperatures
(b) evaluating velocities of reaction at two different temperatures
(c) evaluating rate constant at standard temperature
(d) changing concentration of reactants. 
Answer. A

Question. By the action of enzymes, the rate of biochemical reaction
(a) does not change
(b) increases
(c) decreases
(d) either (a) or (c).
Answer. B

Question. An increase in the concentration of the reactants of a reaction leads to change in
(a) activation energy
(b) heat of reaction
(c) threshold energy
(d) collision frequency.
Answer. D

SA (II) QUESTIONS (3- MARK QUESTIONS)

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