CBSE Class 12 Chemistry Chemical Kinetics MCQs Set E

Question: The conversion of A to B follows second order kinetics, doubling the concentration of A will increase the rate of formation of B by a factor of
a) 4
b) 2
c) 1/4
d) 1/2
Answer: a

Question: The unit of second order reaction rate constant is
a) L⁻¹ mol s⁻¹
b) L⁻² mol⁻² s⁻¹
c) L mol⁻¹ s⁻¹
d) s⁻¹
Answer: c

Question: The half-life of a reaction is halved as the initial concentration of the reactant is doubled. The order of the reaction is
a) 0.5
b) 1
c) 2
d) 0
Answer: c

Question: Decay of 92U²³⁵ is …… order reaction.
a) zero
b) first
c) second
d) third
Answer: b

Question: In a reaction A + B → C, the rate expression is R = k[A][B]². If the concentration of both the reactants is doubled at constant volume then the rate of the reaction will be
a) eight times
b) double
c) quadruple
d) triple
Answer: a

Question: The half-life of two samples are 0.1 and 0.8 s. Their respective concentrations are 400 and 50 respectively. The order of the reaction is
a) 0
b) 2
c) 1
d) 4
Answer: b

Question: A(g) →Δ P(g) + Q(g) + R(g), follows first order kinetics with a half-life of 69.3 s at 500 °C. Starting from the gas A enclosed in a container at 500 °C and at a pressure of 0.4 atm, the total pressure of the system after 230 s will be
a) 1.15 atm
b) 1.32 atm
c) 1.22 atm
d) 1.12 atm
Answer: d

Question: 75% of a first order reaction is completed in 30 min. What is the time required for 93.75% completion of the reaction (in minutes)?
a) 45
b) 120
c) 90
d) 60
Answer: d

Question: For a first order reaction of k = 6.2 × 10⁻⁵ s⁻¹, t₃/₄ will be
a) 4.65 × 10⁻⁵ s
b) 2.24 × 10⁻⁴ s
c) 2.24 × 10⁻⁵ s
d) 8.27 × 10⁻⁵ s
Answer: b

Question: The half-life of two samples are 0.1 and 0.4 seconds. Their respective concentrations are 200 and 50, respectively. What is the order of reaction?
a) 0
b) 2
c) 1
d) 4
Answer: b

Question: The half-life period of a first order reaction is 69.3 s. What is the rate constant?
a) 0.01 s^-1
b) 0.1 s^-1
c) 1 s^-1
d) 10 s^-1
Answer: a

Question: In the first order reaction, 75% of the reactant gets disappeared in 1.386 h. The rate constant of the reaction is
a) 3.0 x 10^-3 s^-1
b) 2.8 x 10^-4 s^-1
c) 17.2 x 10^-3 s^-1
d) 1.8 x 10^-3 s^-1
Answer: b

Question: Which one of the following is a second order reaction?
a) H₂ + Br₂ → 2HBr
b) NH₄NO₃ → N₂ + 3H₂O
c) H₂ + Cl₂ →Sunlight 2HCI
d) CH₃COOCH₃ + NaOH → CH₃COONa + CH₃OH
Answer: d

Question: For the reaction, 2A + B ➔ C + D, the order of reaction is
a) one with respect to [B]
b) two with respect to [A]
c) three
d) Cannot be predicted
Answer: d

Question: For a zero order reaction
a) t_1/2 ∝ R₀
b) t_1/2 ∝ 1/ R₀
c) t_1/2 ∝ R₀²
d) t_1/2 ∝ 1/ R₀²
Answer: a

Question: The half-life period of a first order chemical reaction is 6.93 min. The time required for the completion of 99% of the chemical reaction will be (log 2 = 0.301)
a) 230.3 min
b) 23.03 min
c) 46.06 min
d) 460.6 min
Answer: c

Question: Consider an endothermic reaction X → Y with the activation energies Eb and Ef for the backward and forward reactions, respectively. In general
a) there is no definite relation between Eb and Ef
b) Eb = Ef
c) Eb > Ef
d) Eb < Ef
Answer: d

Question: For a reaction, the rate constant is 2.34 s-1. The half-life period for the reaction is
a) 0.30 s
b) 0.60 s
c) 3.3 s
d) data is insufficient
Answer: a

Question: The rate of first order reaction is 1.5 x 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: In a reaction, the threshold energy is equal to
a) activation energy + normal energy of reactants
b) activation energy – normal energy of reactants
c) normal energy of reactants – activation energy
d) average kinetic energy of molecules of reactants
Answer: a

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

Question: At 500 K, the half-life period of a gaseous reaction at an initial pressure of 80 kPa is 350 s. When the pressure is 40 kPa, the half-life period is 175 s. The order of the reaction is
a) zero
b) one
c) two
d) three
e) half
Answer: a

Question: The t_1/2 of the first order reaction is
a) dependent of initial concentration
b) directly proportional to initial concentration
c) indirectly proportional to initial concentration
d) independent of initial concentration
Answer: d

Question: The concentration of a reactant X decreases from 0.1 M to 0.005 M in 40 min. If the reaction follows first order kinetics, the rate of the reaction when the concentration of X is 0.01 M will be
a) 1.73 x 10^-4 M min^-1
b) 3.47 x 10^-4 M min^-1
c) 3.47 x 10^-5 M min^-1
d) 7.5 x 10^-4 M min^-1
Answer: d

Question: A reaction involving A, B and C as reactants is found to obey the rate law, rate = k[A]x[B]Y[C]z. When the concentrations of A, B and C are doubled separately, the rate is also found to increase two, zero and four times respectively. The overall order of the reaction is
a) 1
b) 2
c) 3
d) 4
Answer: c

Question: The energies of activation for forward and reverse reactions for A₂ + B₂ ⇌ 2AB are 180 kJ mol–1 and 200 kJ mol^–1 respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by 100 kJ mol^–1. The enthalpy change of the reaction (A₂ + B₂ → 2AB) in the presence of a catalyst will be (in kJ mol^–1)
a) 20
b) 300
c) 120
d) 280
Answer: a

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) L mol^-1 s^-1
b) no unit
c) mol L^-1 s^-1
d) s^-1
Answer: a

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 the reaction will be as
a) 1/2m+n
b) (m + n)
c) (n – m)
d) 2(n – m)
Answer: d

Question: The rate of the reaction A ➔ products, at the initial concentration of 3.24 x 10^-2 M is nine times its rate at another initial concentration of 1.2 x 10^-3 M. The order of the reaction is
a) 1/2
b) 2/3
c) 3/2
d) 3/4
e) 1/3
Answer: d

Question: Activation energy of the reaction is
a) the energy released during the reaction
b) the energy evolved when activated complex is formed
c) minimum amount of energy needed to overcome the potential barrier
d) the energy needed to form one mole of the product
Answer: c

Question: 1/[A]² versus time is a straight line. Order of reaction is
a) first
b) second
c) zero
d) third
Answer: b

Question: In most cases, for a rise of 10K temperature the rate constant is doubled to tripled. This is due to the reason that
a) collision frequency increases by a factor of 2 to 3
b) fraction of molecules possessing threshold energy increases by a factor of 2 to 3
c) Activation energy is lowered by a factor of 2 to 3
d) none of the options
Answer: b

Question: For the exothermic reaction A + B → C + D, ΔH is the heat of reaction and Ea is the energy of activation. The energy of activation for the formation of A + B will be
a) Ea
b) ΔH
c) Ea + ΔH
d) ΔH – Ea
Answer: c

Question: A catalyst increases rate of reaction by
a) decreasing enthalpy
b) decreasing internal energy
c) decreasing activation energy
d) increasing activation energy
Answer: c

Question: According to which theory activation energy and proper orientation of the molecules together determine the criteria for an effective collision?
a) Arrhenius theory
b) Activated complex theory
c) Collision theory
d) Both (a) and (c)
Answer: c

Question: Activation energy of a chemical reaction can be determined by ___________
a) determining the rate constant at standard temperature
b) determining the rate constants at two temperatures
c) determining probability of collision
d) using catalyst
Answer: b

Question: Consider the following statements in respect of zero order reaction.
I. The rate of the reaction is independent of reactant concentration.
II. The rate of the reaction is independent of temperature.
III. The rate constant of the reaction is independent of temperature.
IV. The rate constant of the reaction is independent of reactant concentration.
Choose the correct statement/s. 
a) Only I
b) I and II
c) III and IV
d) I and Ill
e) I and IV
Answer: e

Question: A hypothetical reaction, A₂ + B₂ → 2AB follows the mechanism as given below,
A₂ ⇌ A + A (fast)
A + B₂ → AB + B (slow)
A + B → AB (fast)
The order of the overall reaction is
a) 2
b) 1
c) 1 1/2
d) 0
Answer: c

Question: Consider the reaction,
Cl₂ (aq) + H₂S(aq) ➔ S(s) + 2H⁺ (aq) + 2Cl^– (aq) The rate equation for this reaction is, rate= k [Cl₂ ][H₂SJ Which of these mechanisms is/are consistent with this rate equation?
I. Cl₂ + H₂S ➔ H⁺ + CI^– + Cl⁺ + HS^– (slow)
Cl⁺ + HS ➔ H⁺ + CI^– + S(fast)
II. H₂S ⇌ H+ + HS (fast equilibrium)
Cl₂ + HS ➔ 2CI^– + H⁺ + S(slow) 
a) Only II
b) Both I and II
c) Neither I nor II
d) Only I
Answer: d

Question: For the reaction system,
2NO(g) + O₂(g) → 2NO₂(g)
volume is suddenly reduced to half its value by increasing the pressure on it. If the reaction is of first order with respect to O₂ and second order with respect to NO; the rate of reaction will 
a) diminish to one-fourth of its initial value
b) diminish to one-eighth of its initial value
c) increase to eight times of its initial value
d) increase to four times of its initial value
Answer: c

Question: Consider the following statements, The rate law for the acid catalysed hydrolysis of an ester being given as Rate = k [H⁺ ][ester] = k’ [acid]. If the acid concentration is doubled at constant ester concentration 
I. The second order rate constant, k is doubled.
II. The pseudo first order rate constant, k is doubled.
III. The rate of the reaction is doubled.
Which of the above statements are correct ? 
(a) I and II
(b) II and III
(c) I and III
(d) I,II and III
Answer: b