# MCQ Questions for Class 12 Chemistry Chapter 4 Chemical Kinetics with Answers

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## Chemical Kinetics Class 12 MCQs Questions with Answers

Question 1.
For a chemical reaction, X + 2Y → Z, if the rate of appearance of Z is 0.50 moles per litre per hour, then the rate of disappearance of Y is
(a) 0.5 mol L-1 hr-1
(b) 1.0 mol L-1 hr-1
(c) 0.25 mol L-1 hr-1
(d) cannot be predicted

Answer: (b) 1.0 mol L-1 hr-1

Question 2.
For the reaction, NO2 (g) + CO (g) → NO (g), the correct expression for the rate of the reaction is
(a) rate = $$\frac {-d[NO_2]}{dt}$$
(b) rate = $$\frac {-d[CO_2]}{dt}$$
(c) rate = $$\frac {d[NO_2]-d[CO]}{dt}$$
(d) rate = $$\frac {d[CO_2]}{dt}$$

Answer: (a) rate = $$\frac {-d[NO_2]}{dt}$$

Question 3.
The rate of a reaction is primarily determined by the slowest step. This step is called
(a) rate determining step
(b) activation step
(c) reaction rate step
(d) none of these.

Answer: (a) rate determining step

Question 4.
The reaction of high molecularity are rare because
(a) Many body collisions have a low probability.
(b) Many body collisions are not favoured energetically.
(c) Activation energy of many body collisions is very large
(d) Very high concentration is required for such reactions.

Answer: (a) Many body collisions have a low probability.

Question 5.
For a chemical reaction A → B, it is found that the rate of the reaction quardruples when the concentration of A is doubled. The rate expression for the reaction is, rate = k [A]n where the value of n is
(a) 1
(b) 2
(c) 0
(d) 3

Question 6.
On increasing the temperature of the reacting system by 10° the rate of reaction almost becomes double. The most appropriate reason for this is that
(a) Activation energy decreases by increases of temperature
(b) The fraction of molecules having threshold energy increases
(c) Collision frequency increases
(d) The value of threshold energy decreases.

Answer: (b) The fraction of molecules having threshold energy increases

Question 7.
The half-life period of any first order reaction
(a) is half the specific rate constant
(b) is always the same irrespective of the reaction
(c) is independent of initial concentration
(d) in directly proportional to initial concentration of reactants.

Answer: (c) is independent of initial concentration

Question 8.
The dimensions of rate constant of 2nd order reaction involves
(a) concentration
(b) concentration and time
(c) time only
(d) neither time nor concentration.

Answer: (b) concentration and time

Question 9.
A zero order reaction A → Products, has rate constant 10-2 mole L-1 s-1. If a process is started with 10 moles of A in a one litre vessel, the number of moles of reactant after 10 minutes will be
(a) 10
(b) 5
(c) 6
(d) 4.

Question 10.
For which of the following reactions, the temperature coefficient is maximum?
(a) A → B : Ea = 50 kJ
(b) P → Q : Ea = 40 kj
(c) X → Y : Ea = 60kJ
(d) W → Z : Ea = 80kJ

Answer: (d) W → Z : Ea = 80kJ

Question 11.
A hypothetical reaction 2p + q → s + r has rate constant as 2.0 × 10-3 mol L-1 s-1. The order of the reaction is
(a) unpredictable
(b) zero
(c) one
(d) two

Question 12.
The ratio t7/8 : t1/2 for the first order is
(a) 3
(b) 5
(c) 2
(d) 7

Question 13.
The molecularity of the reaction cannot be
(a) 1
(b) 2
(c) 1.5
(d) 3.

Question 14.
For the first order reaction, the half-life is independent of
(a) catalyst
(b) temperature
(c) both catalyst and temperature
(d) initial concentration of reactants.

Answer: (d) initial concentration of reactants.

Question 15.
For a certain reaction aA → bB, the rate of reaction is doubled when the concentration of A is increased by four times. The rate ot reaction is equal to
(a) k[A]a
(b) k[A]1/2
(c) k[A]1/a
(d) k[A].

Question 16.
The rate law for the chemical reaction, 2NO2Cl → 2NO2 + Cl2 is r = k[NO2Cl]. Which of the following is rate controlling step?
(a) NO2 + Cl → NO2Cl
(b) NO2Cl + Cl → NO2 + Cl2
(c) NO2Cl → NO2 + Cl
(d) 2NO2Cl → 2NO2 + Cl2.

Answer: (c) NO2Cl → NO2 + Cl

Question 17.
Rate constant of a reaction depends upon
(a) Temperature
(b) time
(c) initial concentration
(d) none

Question 18.
DDT on exposure to water decomposes. Half-life = 10 years. How much time will it take for its 90% decomposition?
(a) 50 years
(b) 70 years
(c) 500 years
(d) 700 years.

Answer: (b) 70 years

Question 19.
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 mm
(b) 23.1mm
(c) 8.73 mm
(d) 7.53 mm

Question 20.
The rate equation for the reaction 2A + B → C is found to be: rate = k [A] [B]. The correct statement inxelation to this reaction is that the
(a) unit of R must be s-1
(b) t1/2 is constant
(c) rate of formation of C is twice the rate of disappearance of A.
(d) value of k is independent of the initial concentration of A and B.

Answer: (d) value of k is independent of the initial concentration of A and B.

Question 21.
The reaction 2 SO2 (g) + O2 (g) ⇌ SO3 (g) is carried out in 1 dm³ vessel and 2 dm³ vessel separately. The ratio of the reaction velocities will be
(a) 1 : 8
(b) 1 : 4
(c) 4 : 1
(d) 8 : 1

Answer: (d) 8 : 1

Question 22.
A + 2B → C + D. If- d [A]/dt = 5 × 10-4 mol L-1 s-1, Then – $$\frac {d[B]}{dt}$$is
(a) 2.5 × 10-4 mol L-1 s-1
(b) 5.0 × 10-4 mol L-1 s-1
(c) 2.5 × 10-3 mol L-1 s-1
(d) 1.0 × 10-3 mol L-1 s-1

Answer: (d) 1.0 × 10-3 mol L-1 s-1

Question 23.
Which of the following statements is not correct for order of a reaction?
(a) Order of a reaction can be determined experimentally.
(b) It is the sum of the powers of concentration terms in the rate law expression.
(c) It does not necessarily depend on the stoichiometric coefficients.
(d) Order of a reaction cannot be fractional.

Answer: (d) Order of a reaction cannot be fractional.

Question 24.
t1/4 can be taken as the time taken for the concentration of a reactant to drop to 3/4 of its initial value. If the rate constant for a first order reaction is K, then t1/4 can be written as
(a) 0.10/K
(b) 0.29/K
(c) 0.69/K
(d) 0.73/K

Question 25.
Collision Theory is applicable to
(a) First order reactions
(b) Zero order reactions
(c) Biomolecular reactions
(d) Intramolecular reactions.

Answer: (c) Biomolecular reactions

Question 26.
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) 1 hour

Question 27.
The potential energy diagram in the reaction R → P is given. ∆H° of the reaction corresponds to the energy.

(a) a
(b) b
(c) c
(d) a + b

Question 28.
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 the reactant B is
(a) 2
(b) -1
(c) 1
(d) -2

Question 29.
For reaction aA → xP, when [A] = 2.2 mM the rate was found to be 2.4 mMs-1. On reducing the concentration of A to half, the rate changes to 0.6 mMs-1. The order of reaction with respect to A is
(a) 1.5
(b) 2.0
(c) 2.5
(d) 3.0

Question 30.
The half-lives of two samples are 0.1 and 0.4 second. Their respective concentrations are 200 and 50 respectively. What is the order of the reaction?
(a) 0
(b) 2
(c) 1
(d) 4

Question 31.
In a first order reaction, the concentration of the reactant decreases from 800 mol/dm³ to 50 mol/dm³ in 2 × 104 sec. The rate constant
for the reaction in sec-1
(a) 2 × 104
(b) 3.45 × 10-5
(c) 1.386 × 10-4
(d) 2 × 10-4

Answer: (c) 1.386 × 10-4

Question 32.
For the reaction A + B → C + D, doubling the concentration ofboth the reactants increases the reaction rate by 8 times and doubling the concentration of only B simply doubles the reaction rate. The rate law is given as
(a) r = k[A]$$\frac {1}{2}$$ [B]$$\frac {1}{2}$$
(b) r = k [A] [B]²
(c) r – k [A]² [B]
(d) r = k [A] [B]

Answer: (c) r – k [A]² [B]

Question 33.
In Arrhenius plpt, intercept is equal to
(a) -Ea/R
(b) ln A
(c) ln k
(d) log10 a

Answer: (b) ln A

Question 34.
The rate constant for the reaction 2N2O5 → 4NO2 + O2 is 3.0 × 10-5 sec-1. If the rate is 2.40 × 10-5 mol litre-1 sec-1, then the concentration of N2O5 (in mol litre-1) is:
(a) 1.4
(b) 1.2
(c) 0.04
(d) 0.8

Question 35.
When a biochemical reaction is carried out in laboratory from outside of human body in absence of enzyme, then the rate of reaction obtained is 10-6 times, then activation energy of reaction in presence of enzyme is:
(a) 6/RT
(b) Pis required
(c) Different from Ea obtained in the laboratory
(d) Cannot, say anything

Answer: (c) Different from Ea obtained in the laboratory

Question 36.
If ‘I’ is the intensity of absorbed light and ‘C’ is the concentration of AB for the photochemical process AB + hv → AB+, the rate of formation of AB* is directly proportional to:
(a) C
(b) l
(c) l2
(d) Cl.

Question 37.
In the following reaction, how is the rate of appearance of the underlined product related to the rate of disappearance of the underlined reactant?
BrO$$_{3}^{-}$$ (aq) + 5 Br +6H+ → 3 Br2 (1) + 3H2O (l)
(a) $$\frac {d[Br_2]}{dt}$$ = -d [Br]/dt
(b) $$\frac {d[Br_2]}{dt}$$ = $$\frac {3}{5}$$ $$\frac {d[Br^-]}{dt}$$
(c) d [Br2]/dt = $$\frac {3}{5}$$ d [Br]/dt
(d) $$\frac {d[Br_2]}{dt}$$ = –$$\frac {5}{3}$$ d [Br]/dt

Answer: (c) d [Br2]/dt = $$\frac {3}{5}$$ d [Br]/dt