CBSE Class 12 Chemistry Chemical Kinetics MCQs Set G

Question. A chemical reaction was carried out at 300 K and 280 K. The rate constants were found to be k₁ and k₂ respectively. then
(a) k₁ = 4k₁
(b) k₂ = 2k1
(c) k₂ = 0.25 k₁
(d) k₂ = 0.5 k₁
Answer: c

Question. Consider the reaction, 2A + B → products. When concentration of B alone was doubled, the half-life did not change. When the 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^–1 s^–1
(c) no unit
(d) mol L^–1 s^–1.
Answer: b

Question. For the reaction H₂(g) + Br₂ (g) → 2HBr (g), the experimental data suggest, rate = k[H₂][Br₂]^1/2. The molecularity and order of the reaction are respectively
(a) 2, 3/2
(b)3/2,3/2
(c) 1, 1
(d) 1, 1/2
Answer: a

Question. Order of reaction is decided by
(a) temperature
(b) mechanism of reaction as well as relative concentration of reactants
(c) molecularity
(d) pressure
Answer: b

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

Question. The rate constant for a first order reaction whose half-life, is 480 seconds is :
(a) 2.88 × 10^–3 sec^–1
(b) 2.72 × 10^–3 sec^–1
(c) 1.44 × 10 ^–3 sec^–1
(d) 1.44 sec^–1
Answer: c

Question. Which of the following statements best describes how a catalyst works?
a) A catalyst changes the potential energies of the reactants and products.
(b) A catalyst decreases the temperature of the reaction which leads to a faster rate.
(c) A catalyst lowers the activation energy for the reaction by providing a different reaction mechanism.
(d) A catalyst destroys some of the reactants, which lowers the concentration of the reactants.
Answer: c

Question. Velocity constant k of a reaction is affected by
(a) change in the concentration of the reactant
(b) change of temperature
(c) change in the concentration of the product
(d) None of the above
Answer: b

Question. The decomposition of N₂O₅ occurs as 2N₂O₅ → 4NO₂ + O₂ and follows Ist order kinetics, hence:
(a) the reaction is unimolecular
(b) the reaction is bimolecular
(c) t_1/2 ∝ a⁰
(d) None of these
Answer: c

Question. The value of rate constant of a pseudo first order reaction _________.
(a) depends on the concentration of reactants present in small amount.
(b) depends on the concentration of reactants present in excess.
(c) is independent on the concentration of reactants.
(d) depends only on temperature.
Answer: b

Question. Rate of a reaction can be expressed by Arrhenius equation as : k = Ae^{-E_a / RT} In this equation, Ea represents
(a) the total energy of the reacting molecules at a temperature, T
(b) the fraction of molecules with energy greater than the activation energy of the reaction
(c) the energy below which all the colliding molecules will react
(d) the energy below which colliding molecules will not react 
Answer: d

Question. How can be activation energy for a reaction be determined graphically?
(a) Plot k versus T, the slope of the line will be equal to E_a
(b) Plot 1/[A]_t versus t, the slope of the line will be equal to E_a
(c) Plot ln [A]_t versus t, the slope of the line will be equal to – E_a
(d) Plot ln k versus 1/T, the slope of the line will be equal to – E_a / R
Answer: d

Question. Nitrogen monoxide, NO, reacts with hydrogen, H₂, according to the following equation:
2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g)
If the mechanism for this reaction were,
2NO(g) + H₂(g) → N₂(g) + H₂O₂(g) ; slow
H₂O₂(g) + H₂(g) → 2H₂O(g) ; fast
Which of the following rate laws would we expect to obtain experimentally?
(a) Rate = k[H₂O₂][H₂]
(b) Rate = k[NO]²[H₂]
(c) Rate = k[NO]²[H₂]²
(d) Rate = k[NO][H₂]
Answer: c

Question. The minimum energy required for the reacting molecules to undergo reaction is :
(a) potential energy
(b) kinetic energy
(c) thermal energy
(d) activation energy
Answer: d

Question. Which of the following is not a first order reaction ?
(a) Hydrogenation of ethene
(b) Natural radioactive decay of unstable nuclei
(c) Decomposition of HI on gold surface
(d) Decomposition of N₂O
Answer: c

Question. In an exothermic reaction if ΔH is the enthalpy then activation energy is
(a) more than ΔH
(b) less than ΔH
(c) equal to ΔH
(d) none of the above
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. Which of the following influences the rate of a chemical reaction performed in solution?
(a) Temperature
(b) Activation energy
(c) Presence of a catalyst
(d) All of the above influence the rate
Answer: d

Question. In a reversible reaction the energy of activation of the forward reaction is 50 kcal. The energy of activation for the reverse reaction will be
(a) < 50 kcal
(b) either greater than or less than 50 kcal
(c) 50 kcal
(d) > 50 kcal
Answer: b

Question. According to collision theory, which of the following is NOT a true statement concerning a catalyst?
(a) A catalyst changes the temperature of reaction.
(b) The mechanism of a reaction will change when a catalyst is added.
(c) A catalyst provides a different activation energy for a reaction.
(d) A catalyst changes the speed of a reaction, but not the equilibrium constant.
Answer: a

Question. The order of a reaction, with respect to one of the reacting component Y, is zero. It implies that:
(a) the reaction is going on at a constant rate
(b) the rate of reaction does not vary with temperature
(c) the reaction rate is independent of the concentration of Y
(d) the rate of formation of the activated complex is zero
Answer: c

Question. A reaction having equal energies of activation for forward and reverse reaction has :
(a) ΔG = 0
(b) ΔH = 0
(c) ΔH = ΔG = ΔS = 0
(d) ΔS = 0
Answer: b

Question. The reason for almost doubling the rate of reaction on increasing the temperature of the reaction system by 10°C is
(a) the value of threshold energy increases
(b) collision frequency increases
(c) the fraction of the molecule having energy equal to threshold energy or more increases
(d) activation energy decreases
Answer: c

Question. Which of the following has been used to explain the subject of chemical kinetics
(a) Collision theory of bimolecular reactions
(b) The activated complex theory
(c) Arrhenius equation
(d) All of these
Answer: d

Question. A reaction proceeds by first order, 75% of this reaction was completed in 32 min. The time required for 50% completion is
(a) 8 min
(b) 16 min
(c) 20 min
(d) 24 min
Answer: b

MATCHING TYPE QUESTIONS

Question. Match the columns
Column – I                                             Column – II
(A) Number of collisions per              (p) Effective collisions.
     second per unit volume
     of the reaction mixture.
(B) Fraction of molecules                  (q) Collision frequency
     with energies equal to
     or greater than Ea
(C) Molecules for which                     (r) e^-E_a /RT
     Rate =  Z_{ABe^{-Ea /RT}}
     shows significant deviations
(D) Collision in which molecules      (s) Complex molecules
     collide with sufficient K.E.
     and proper orientation.
(a) A – (q), B – (r), C – (s), D – (p)
(b) A – (r), B – (q), C – (s), D – (p)
(c) A – (q), B – (s), C – (r), D – (p)
(d) A – (q), B – (r), C – (p), D – (s)
Answer: a

Question. Match the columns
Column-1                                          Column-II
(A) Zero order reaction                 (p) L mole^–1 sec^–1
(B) First order reaction                 (q) mole L^–1 sec^–1
(C) Second order reaction            (r) sec^–1
(a) A – (q), B – (r) ,C – (p)
(b) A – (q), B – (p) ,C – (r)
(c) A – (p), B – (q) ,C – (r)
(d) A – (p), B – (r) ,C – (q)
Answer: b

Question. Match the columns
Column-I                                                          Column-II
(A) Mathematical expression for rate           (p) rate constant
     of reaction
(B) Rate of reaction for zero order                (q) rate law
     reaction is equal to
(C) Units of rate constant for zero                 (r) order of slowest
     order reaction is same as that of step
(D) Order of a complex reaction is                (s) rate of reaction
     determined by
(a) A – (q), B – (p), C – (s), D – (r)
(b) A – (r), B – (p), C – (s), D – (q)
(c) A – (q), B – (s), C – (p), D – (r)
(d) A – (p), B – (q), C – (s), D – (r)
Answer: a

Question. Match the columns
Column-I                                                   Column-II
(A) The decomposition                     (p) Zero order reaction
     of gaseous ammonia
     on a hot platinum
     surface
(B) The thermal                               (q) Pseudo first order reaction.
     decomposition of HI                             
     on gold surface
(C) All natural and                          (r) Zero order reaction at high pressure
     artificial radioactive                              
     decay of unstable
     nuclei
(D) Inversion of cane sugar            (s) First order reaction.
(a) A – (r), B – (p), C – (s), D – (q)
(b) A – (r), B – (s), C – (q), D – (p)
(c) A – (q), B – (s), C – (p), D – (r)
(d) A – (q), B – (p), C – (s), D – (p)
Answer: a

Question. Match the columns.
Column-I                                              Column-II
(A) Catalyst alters the rate             (p) cannot be fraction or zero
      of reaction
(B) Molecularity                             (q) proper orientation is not there always.
(C) Second half life of first             (r) by lowering the activation enrgy
      order reaction
(D) Energetically favourable         (s) is same as the first
     reactions are sometimes
     slow
(a) A – (q), B – (r), C – (s), D – (p)
(b) A – (r), B – (s), C – (p), D – (q)
(c) A – (r), B – (p), C – (s), D – (q)
(d) A – (p), B – (r), C – (s), D – (q)
Answer: c

CRITICAL THINKING TYPE QUESTIONS

Question. Consider a reaction aG + bH → Products. When concentration of both the reactants G and H is doubled, the rate increases by eight times. However, when concentration of G is doubled keeping the concentration of H fixed, the rate is doubled. The overall order of the reaction is
(a) 0
(b) 1
(c) 2
(d) 3
Answer: d

Question. The integrated rate equations can be determined for
(a) zero order reactions
(b) first order reactions
(c) second order reactions
(d) Both (a) and (b)
Answer: d

Question. The decomposition of ammonia on tungsten surface at 500 K follows zero order kinetics. The half-life period of this reaction is 45 minutes when the initial pressure is 4 bar. The half-life period (minutes) of the reaction when the initial pressure is 16 bar at the same temperature is
(a) 120
(b) 60
(c) 240
(d) 180
Answer: d

Question. The rate constant, the activation energy and the arrhenius parameter of a chemical reaction at 25°C are 3.0 × 10^–4s^–1,104.4 kJ mol^–1 and 6.0 × 10¹⁴ s^–1 respectively. The value of the rate constant as T → ∞  is
(a) 2.0 × 10¹⁸ s^–1
(b) 6.0 × 10¹⁴ s^–1
(c) Infinity
(d) 3.6 × 10³⁰ s^–1
Answer: b

Question. In a 1st order reaction, reactant concentration C varies with time t as :
(a) 1/C increases linearly with t
(b) log C decreases linearly with t
(c) C decreases with 1/t
(d) log C decreases with 1/t
Answer: b

Question. The reaction of hydrogen and iodine monochloride is given as:
H₂ (g) + 2ICl(g)  →  2HCl(g) + I₂ (g)
The reaction is of first order with respect to H₂(g) and ICI(g),
following mechanisms were proposed.
Mechanism A:
H₂ (g) + 2ICl(g) → 2HCl(g) + I₂ (g)
Mechanism B:
H₂ (g) + ICl(g) → HI(g);slow
HI(g) + ICl(g) → HCl(g) + I₂ (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. Collision theory is used to explain how chemical species undergo a reaction. Using this theory and the kinetic molecular model, which of the following does NOT influence the rate of a chemcial reaction?
(a) The temperature of the system
(b) The geometry or orientation of the collision
(c) The velocity of the reactants at the point of collision
(d) All of the above influence the rate
Answer: d

Question. Diazonium salt decomposes as
C₆H₅N₂⁺Cl^– + C₆H₅Cl + N₂ 
At 0°C, the evolution of N2 becomes two times faster when the initial concentration of the salt is doubled. Therefore, it is
(a) a first order reaction
(b) a second order reaction
(c) independent of the initial concentration of the salt
(d) a zero order reaction
Answer: a

Question. For a first order reaction A → P, the temperature (T) dependent rate constant (k) was found to follow the equation log k = – (2000) 1/T + 6.0 . The pre-exponential factor
A and the activation energy Ea, respectively, are
(a) 1.0 × 10⁶ s–1 and 9.2 kJ mol^–1
(b) 6.0 s^–1 and 16.6 kJ mol^–1
(c) 1.0 × 106 s^–1 and 16.6 kJ mol^–1
(d) 1.0 × 106 s^–1 and 38.3 kJ mol^–1
Answer: d

Question. During decomposition of an activated complex.
(i) energy is always released
(ii) energy is always absorbed
(iii) energy does not change
(iv) reactants may be formed
(a) (i), (ii) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii), (iii) and (iv)
Answer: b

Question. A substance ‘A’ decomposes by a first order reaction starting initially with [A] = 2.00 M and after 200 min, [A] becomes 0.15 M. For this reaction t_1/2 is
(a) 53.72 min
(b) 50.49 min
(c) 48.45 min
(d) 46.45 min
Answer: a

Question. CHCl₃ + Cl₂ → CCl₄ + HCl Rate law for above reaction will be
Rate = k[CHCl₃][Cl₂ ]^1/2
On the basis of information provided which of the following option will be correct ?
(a) Rate law for any chemical reaction can be predicted accurately by looking at balanced chemical equation.
(b) Rate law for a chemical reaction has to determine experimentally.
(c) Either determined experimentally or obtained from balanced chemical reaction, rate law will be same.
(d) None of the above is correct.
Answer: b

Question. The initial rates of reaction
3A + 2B + C → Products, at different initial
concentrations are given below:
Initial rate,       [A]0, M     [B]0, M     [C]0, M
Ms^–1
5.0 × 10^–3        0.010         0.005         0.010
5.0 × 10^–3        0.010         0.005         0.015
1.0 × 10^–2        0.010         0.010         0.010
1.25 × 10^–3      0.005         0.005         0.010
The order with respect to the reactants, A, B and C are respectively
(a) 3, 2, 0
(b) 3, 2, 1
(c) 2, 2, 0
(d) 2, 1, 0
Answer: d

Question. The following data pertains to reaction between A and B :
S.N o. [A] mol L^–1     [B] mol L^–1       Rate (mol L^–1 time^–1)
1 1.0 × 10^–2             2.0 × 10^–2          2.0 × 10^–4
2 2.0 × 10^–2               2.0 × 10^–2          4.0 × 10^–4
3 2.0 × 10^–2             4.0 × 10^–2          8.0 × 10^–4
Which of the following inference(s) can be drawn from the above data ?
(i) Rate constant of the reaction is 1.0 × 10^–4.
(ii) Rate law of the reaction is : rate = k[A][B]
(iii) Rate of reaction increases four times on doubling the concentration of both the reactants.
Select the correct answer using the codes given below :
(a) (i), (ii) and (iii)
(b) (i) and (ii)
(c) (ii) and (iii)
(d) (iii) only
Answer: c

Question. For the first order reaction
C₂H₄O(g) → CH₄ (g) + CO(g) ,the initial pressure of
C₂H₄O(g) is 80 torr and total pressure at the end of 20 minutes is 120 torr. The time needed for 75% decomposition of C₂H₄O would be :
(a) 20 minutes
(b) 40 minutes
(c) 80 minutes
(d) 120 minutes
Answer: b

Question. In a zero-order reaction for every 10° 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. If half-life of a substance is 5 yrs, then the total amount of substance left after 15 years, when initial amount is 64 grams is
(a) 16 grams
(b) 2 grams
(c) 32 grams
(d) 8 grams.
Answer: d

Question. The activation energy for a hypothetical reaction, A → Product, is 12.49 kcal/mole. If temperature is raised from 295 to 305, the rate of reaction increased by
(a) 60%
(b) 100%
(c) 50%
(d) 20%
Answer: b

Question. Which of the following statements is not correct for the catalyst?
(a) It catalyses the forward and backward reaction to the same extent.
(b) It alters ΔG of the reaction.
(c) It is a substance that does not change the equilibrium constant of a reaction.
(d) It provides an alternate mechanism by reducing activation energy between reactants and products.
Answer: b

Question. Consider the following reaction at 25°C:
(CH₃)₃COH(l) + HCl(aq) → (CH₃)₃CCl(l) + H₂O(l)
The experimentally determined rate law for this reaction indicates that the reaction is of first order in (CH₃)₃COH and that the reaction is of first order overall. Which of the following would produce an increase in the rate of this reaction?
(a) Increasing the concentration of (CH₃)₃COH
(b) Increasing the concentration of HCl
(c) Decreasing the concentration of HCl
(d) Decreasing the concentration of (CH₃)₃CCl
Answer: a

Question. Which of the following statements is incorrect ?
(a) Energy is always released when activated complex decomposes to form products.
(b) Peak of the energy distribution curve corresponds to the most probable potential energy.
(c) Peak of the energy distribution curve corresponds to the most probable kinectic energy.
(d) When the temperature is raised maximum of energy distribution curve moves to higher energy value and broadens out.
Answer: b