CBSE Class 12 Chemistry Chemical Kinetics MCQs Set 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. 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. Raw milk sours in about 4 hat 27°C, but in about 48 h in a refrigerator at 17°C. What is the activation energy for souring of milk?
(a) 78.0 kl mol^-1
(b) 46.21 kl mol^-1
(c) 23.5 kl mol^-1
(d) 80.8 kl mol^-1

Answer : A

Question. A plot of 1/ T versus k for a reaction gives the slope – 1 x 104 K. The energy of activation for the reaction is (Given, R = 8.314K-1 mol^-1)
(a) 83.14 J mol^-1
(b) 1.202 kJ mol^-1
(c) 12.02 J mol^-1
(d) 83.14 kJ mol^-1

Answer : D

Question. The rate constant (k₁ ) of one of the reaction is found to be double that of the rate constant (k₂ ) of another reaction. The relationship between the corresponding activation energies of the two reactions  Ea₁ and E_a2 will be
(a) Ea₁ < E_a2
(b)  Ea₁ > E_a2
(c)  Ea₁ = E_a2
(d)  Ea₁ = 2E_a2

Answer : A

Question. The activation energies of two reactions are E₁ and E₂ (E₁ > E ). If the temperature of the system is increased from T₁ to T₂ , the rate constant of the reactions changes from k₁ to k₂ in the first reaction and k₂ to k₂ in the second reaction. Preruct which of the following expression is correct ?
(a) k₁ / k₁ = k₂ / k₂
(b) k₁ / k₁ > k₂ / k₂
(c) k₁ / k₁ < k₂ / k₂
(d) k₁ / k₁ = k₂ / k₂ = 1
(e) k₁ / k₁ = k₂ / k₂ = 0

Answer : B

Question. Which of the following statement is in accordance with collision theory ?
I. Rate is directly proportional to collision frequency
II. Rate depends upon orientation of atoms
III. Temperature determines the rate
(a) Only III
(b) Only I and II
(c) Only II and III
(d) All of these

Answer : D

Question. If Xis the total number of collisions which a gas molecule register with others per unit time under particular conditions, then the collision frequency of the gas containing N molecules per unit volume is
(a) X / N
(b) NX
(c) 2 NX
(d) NX / 2

Answer : D

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

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 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. The activation energy of exothermic reaction A ➔ B 80 kJ mol^-1. The heat of reaction is 200 kJ mol^-1. The activation energy for the reaction B ➔ A (in kJ mol^-1) will be
(a) 80
(b) 120
(c) 40
(d) 280

Answer : D

Question. By increase in temperature by 10 K, the rate of reaction becomes double. How many times the rate of reaction will be if the temperature is increased from 303K to 353 K?
(a) 4
(b) 8
(c) 16
(d) 32

Answer : D

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 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 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. 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 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. 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. 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