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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
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
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
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
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
Answer
Answer: (b) 2
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
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
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
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.
Answer
Answer: (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
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
Answer
Answer: (b) zero
Question 12.
The ratio t7/8 : t1/2 for the first order is
(a) 3
(b) 5
(c) 2
(d) 7
Answer
Answer: (a) 3
Question 13.
The molecularity of the reaction cannot be
(a) 1
(b) 2
(c) 1.5
(d) 3.
Answer
Answer: (c) 1.5
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
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].
Answer
Answer: (b) k[A]1/2
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
Answer: (c) NO2Cl → NO2 + Cl
Question 17.
Rate constant of a reaction depends upon
(a) Temperature
(b) time
(c) initial concentration
(d) none
Answer
Answer: (a) Temperature
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
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
Answer
Answer: (b) 23.1mm
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
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
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
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
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
Answer
Answer: (b) 0.29/K
Question 25.
Collision Theory is applicable to
(a) First order reactions
(b) Zero order reactions
(c) Biomolecular reactions
(d) Intramolecular reactions.
Answer
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
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
Answer
Answer: (c) c
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
Answer
Answer: (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
Answer
Answer: (b) 2.0
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
Answer
Answer: (b) 2
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
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
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
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
Answer
Answer: (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
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.
Answer
Answer: (b) l
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
Answer: (c) d [Br2]/dt = \(\frac {3}{5}\) d [Br–]/dt
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