CBSE Class 12 Chemistry Chemical Kinetics MCQs Set F

Question. A second order reaction between A and B is elementary reaction:
A + B → Product
rate law expression of this reaction will be:
(a) Rate = K[A][B]
(b) Rate = K[A]⁰[B]²
(c) Rate = K[A]²[B]⁰
(d) Rate = K[A]^3/2[B]^1/2
Answer: a

Question. The rate constant of a reaction becomes equal to the pre exponential factor when:
(a) the absolute temperature is zero
(b) the activation energy is infinity
(c) the absolute temperature is infinity
(d) the activation energy is zero
Answer: c

Question. Rate of which reactions increases with temperature:
(a) of any reactionj
(b) of exothermic reaction
(c) of endothermic reaction
(d) of none
Answer: a

Question. Integer type Question:
For first order reaction: t_99.9/t₅₀ = x, Here x is
(a) 3
(b) 5
(c) 7
(d) 10
Answer: c

Question. A large increase in the rate of reaction for rise in temperature is due to:
(a) Increase in the number of collisions
(b) Increase in the number of activated molecules
(c) Lowering of activation energy
(d) Shortening of the mean free path.
Answer: b

Question. At 227°C, the presence of catalyst causes the activation energy of a reaction to decrease by 4.606 KCal, the rate of the reaction will be increased by:
(a) 2 times
(b) 10 times
(c) 100 times
(d) 1000 times
Answer: c

Question. For a creactionj, the following data were obtained:
Concentration (mol/L) 0.1 0.05 0.025 0.0125
Half life in (sec) 30 29.9 30.1 30
the order of reaction is:
(a) 2
(b) 1
(c) 0
(d) fractional
Answer: b

Question. Which of the following statement is/are correct about order of reaction:
(a) order of reaction is determined experimentally
(b) order of reaction can not have fractional value
(c) it does not necessarily depend on stoichiometric coefficients.
(d) it is the sum of power of concentration terms in rate low expression
Answer: a,c,d

Question. The half life period of a first order reaction is 100° seconds. Its rate constant is:
(a) 0.693 sec^–1
(b) 6.93 × 10^–3 sec^–1
(c) 6.93 × 10^–2 sec^–1
(d) None of these
Answer: b

Question. A first order reaction is 20% complete in one hour. At the end of 3 hrs the extent of the reaction is:
(a) 60%
(b) 52.2%
(c) 48.8%
(d) 44.4%
Answer: c

Question. What is the activation energy for the reverse of this reaction?
N₂O_4(g) → 2NO_2(g)
Data for the given reaction is ΔH = 54 KJ/mol and εa = 57.2 KJ.
(a) – 54 KJ
(b) 3.2 KJ
(c) 60.2 KJ
(d) 111.2 KJ
Answer: b

Question. Radioactive decay is an example of:
(a) first order
(b) second order
(c) zero order
(d) 0.5 order
Answer: a

Question. The decomposition of N₂O₅ occurs as, 2N₂O₅ → 4NO₂ + O₂ and follows first order kinetics, hence:
(a) the reaction is bimolecular
(b) the reaction is unimolecular
(c) tyz ∝ a°
(d) unit of K = mol/L sec⁻¹
Answer: c

Question. For the formation of SO₃ in the following reaction, it is given that
2SO₂ + O₂ → 2SO₃ E_a = Activation energy
SO₂ + 1/2 O₂ → SO₃  E′_a = Activation energy
(a) E_a > E¹_a
(b) E_a < E¹_a
(c) E¹_a = E_a^1/2
(d) E_a = E¹_a
Answer: d

Fill in the blanks type Questions

Question. The reactions taking place in one step is called …………… reactions. 
Answer: elementary

Question. The order of reaction is …………… determined. 
Answer: experimentally

Case Based MCQs

Case III : Read the following and answer the questions given below.

Number of molecules which must collide simultaneously to give product is called molecularity. It is equal to sum of coefficients of reactants present in stoichiometric chemical equation.
For reaction, m₁A + m₂B → Product

Molecularity = [m₁ + m₂]
In complex reaction each step has its own molecularity which is equal to the sum of coefficients of reactants present in a particular step. Molecularity is a theoretical property. Its value is any whole number. Number of concentration terms on which rate of reaction depends is called order of reaction or sum of powers of concentration terms present in the rate equation is called order of reaction.
If rate equation of reaction is : Rate = k C_A^m₁ C_B^m₂
Then order of reaction = m₁ + m₂.
In simple reaction, order and molecularity are same.In complex reaction, order of slowest step is the order of over all reaction. This step is known as rate determining step. Order is an experimental property. Its value may be zero, fractional or negative.

Question. The molecularity of the reaction :
6FeSO₄ + 3H₂SO₄ + KClO₃ → KCl + 3Fe₂(SO₄)₃ + 3H₂O is
(a) 6
(b) 3
(c) 10
(d) 7
Answer: c

Question. Which of the following statements is false in the following?
(a) Order of a reaction may be even zero.
(b) Molecularity of a reaction is always a whole number.
(c) Molecularity and order always have same values for a reaction.
(d) Order of a reaction depends upon the mechanism of the reaction.
Answer: c

Question. The rate of reaction, A + 2B → products, is given by the following equation:
− d[A]/dt =k [A][B ]²
If B is present in large excess, the order of the reaction is
(a) zero
(b) first
(c) second
(d) third.
Answer: b

Read the following and answer the questions given below.

A reaction is said to be of the first order if the rate of the reaction depends upon one concentration term only. For a first order reaction of the type A → Products, the rate of the reaction is given as :
rate = k[A]. The differential rate law is given as :
dA/dt = – k[A]. The integrated rate law is :
ln [A ]/[A ]₀ = – kt, where [A] is the concentration of reactant left at time t and [A]₀ is the initial concentration of the reactant, k is the rate constant.

Question. 50% of a first order reaction is complete in 23 minutes. Calculate the time required to complete 90% of the reaction.
(a) 70.4 minutes
(b) 76.4 minutes
(c) 38.7 minutes
(d) 35.2 minutes
Answer: b

Question. Half-life period of a first order reaction is 10 min. Starting with initial concentration 12 M, the rate after 20 min is
(a) 0.693 × 3 M min^–1
(b) 0.0693 × 4 M min^–1
(c) 0.0693 M min^–1
(d) 0.0693 × 3 M min^–1
Answer: d

Question. The half-life period of a 1st order reaction is 60 minutes. What percentage will be left over after 240 minutes?
(a) 6.25%
(b) 4.25%
(c) 5%
(d) 6%
Answer: a

Question. The unit of rate constant for a first order reaction is
(a) s^–1
(b) mol L^–1 s^–1
(c) L mol^–1 s^–1
(d) L² mol^–2 s^–1
Answer: a

Question. For a first order reaction, (A) → products,the concentration of A changes from 0.1 M to 0.025 M in 40 minutes. The rate of reaction when the concentration of A is 0.01 M, is
(a) 3.47 × 10^–4 M/min
(b) 3.47 × 10^–5 M/min
(c) 1.73 × 10^–4 M/min
(d) 1.73 × 10^–5 M/min
Answer: a