Chemical Kinetics HOTs Class 12 Chemistry

Please refer to Chemical Kinetics HOTs Class 12 Chemistry provided below with solutions. All HOTs for Class 12 Chemistry with answers provided below have been designed as per the latest syllabus and examination petter issued by CBSE, NCERT, KVS. Students of Standard 12 Chemistry should learn the solved HOTS for Class 12 Chemistry provided below to gain better marks in examinations.

Chemical Kinetics Class 12 Chemistry HOTs

Assertion & Reasoning Based MCQs

For question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : For the reaction, 
2N₂O₅ → 4NO₂ + O₂, Rate = k [N₂O₅]
Reason : Rate of decomposition of N₂O₅ is determined by slow step.

Question. Assertion : The decomposition of NH₃ on finely divided platinum surface is first order when the concentration is low, however at higher concentration, the reaction becomes zero order.
Reason : In first order reaction, the rate of reaction is proportional to the first power of the concentration of the reactant. 

Question. Assertion : The order of the reaction           
CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅OH is 1.
Reason : The molecularity of this reaction is 2.

Question.Assertion : Half-life period of a reaction of first order is independent of initial concentration. 
Reason : The time taken for completion of 75% of a first order reaction is equivalent to two half lives.

Question. Assertion : The rate of the reaction is the rate of change of concentration of a reactant or a product.
Reason : Rate of reaction remains constant during the complete reaction.

Question. Assertion : Hydrolysis of cane sugar is a pseudo first order reaction. 
Reason : Water is present in large excess during hydrolysis.

Question. Assertion : The rate law equation can be found only by experiment.
Reason : It can be written from stoichiometric equation.

Question. Assertion : Instantaneous rate of reaction is equal to dx/dt. 
Reason : It is the rate of reaction at any particular instant of time.

Question. Assertion : Rate of reaction can be expressed as rate of change in partial pressure of the gaseous reactants or products.
Reason : Partial pressure of a gas is equal to its concentration. 

Question. Assertion : Chemical kinetics deals with the rate of reaction, the factors affecting the rate of the reaction and the mechanism by which the reaction proceeds.
Reason : Nature of reactants, concentration of reactants, products and catalyst affect the rate of reaction. 

Question. Assertion : Formation of HI is a bimolecular reaction. 
Reason : Two molecules of reactants are involved in this reaction.

Case-based MCQs

I. Read the passage given below and answer the following questions: 

The rate of a reaction, which may also be called its velocity or speed, can be defined with relation to the concentration of any of the reacting substances, or to that of any product of the reaction. If the species chosen is a reactant which has a concentration c at time t the rate is – dc/dt, while the rate with reference to a product having a concentration x at time t is dx/dt. Any concentration units may be used for expressing the rate; thus, if moles per liter are employed for concentration and seconds for the time, the units for the rate are moles litre^–1sec^–1. For gas reactions pressure units are sometimes used in place of concentrations, so that legitimate units for the rate would be (mm of Hg) sec^–1 and atm. sec^–1. The order of a reaction concerns the dependence of the rate upon the concentrations of reacting substances; thus, if the rate is found experimentally to be proportional to the ath power of the concentration of one of the reactants A, to the bth power of the concentration of a second reactant B, and so forth, via.,

rate = k C_A^α  C_A^β
the overall order of the reaction is simply
n = α+ β
Such a reaction is said to be of the αth order with respect to the substance A, the βth order with respect to B.

In the following questions, a statement of Assertion followed by a statement of Reason is given. Choose the correct answer out of the following choices on the basis of the above passage.
(A) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(C) Assertion is correct statement but reason is wrong statement.
(D) Assertion is wrong statement but reason is correct statement.

Question. Assertion: Reactions can occur at different speeds.
Reason: Rate of reaction is also called speed of reaction. 

Question. Assertion: For a chemical reaction, P + 2Q → Products, Rate = k [P]^1/2[Q]¹ so the order of reaction is 1.5
Reason: Order of reaction is the sum of stoichiometric coefficients of the reactants. 

Question. Assertion: Rate of reaction is a measure of change in concentration of reactant with respect to time.
Reason: Rate of reaction is a measure of change in concentration of product with respect to time. 

Question. Assertion: The unit of k is independent of order of reaction.
Reason: For zero order reaction, the unit of k is mol L^–1s^–1. 

II. Read the passage given below and answer the following questions:

The rate of the reaction is proportional to the concentration of the reactant. Hydrogenation of ethene results in the formation of ethane. The rate constant, k for the reaction was found to be 2.5 × 10^–15s^–1. The concentration of the reactant reduces to one-third of the initial concentration in 5 minutes.
The following questions are multiple choice questions. Choose the most appropriate answer:

Question. The rate law equation is:
(A) Rate = k [C₂H₆]
(B) Rate = k [C₂H₄]²
(C) Rate = k [C₂H₄]
(D) Rate = k [C₂H₄]² 

Question. The rate constant of the reaction after 5 minutes is
(A) 0.4290 min^–1
(B) 0.1297 min^–1
(C) 0.2197 min^–1
(D) 0.6591 min^–1

Question. Find the order of reaction.
(A) Zero order
(B) First order
(C) Second order
(D) Fractional order 

Question. The half-life for the reaction is
(A) 2.772 × 10^–24 s
(B) 2.772 × 10^–12 s
(C) 1.386 × 10^–24 s
(D) 1.386 × 10^–12 s

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

Concentration dependence of rate is called differential rate equation. Integrated differential equations give relation between directly measured experimental data i.e. concentration at different times and rate constant. The integrated rate equations are different for the reactions of different reaction orders. The first-order reaction has a rate constant 1.15 × 10^–3s^–1.

The following questions are multiple choice questions. Choose the most appropriate answer:

Question. When the rate constant has same units as the rate of reaction, the order of the reaction is:
(A) Zero order
(B) First order
(C) Second order
(D) Fractional order 

Question. For a reaction, A + H₂O → B Rate ∝ [A]
The order of the reaction is:
(A) Zero order
(B) Fractional order
(C) Pseudo first order
(D) Second order

Question. How long will 5 g of this reactant take to reduce to 3 g?
(A) 222.189 s
(B) 444.379 s
(C) 111.095 s
(D) 888.789 s

Question. Under which condition a bimolecular reaction is kinetically first order reaction?
(A) When two reactants are involved.
(B) When one of the reactants is in excess.
(C) When one of the reactants does not involve in reaction.
(D) None of these 

Question. The first order decomposition of H2O2 are written as (Image 244)
Which of the following relationship is true?
(a) K = K′
(b) K > K′
(c) K > 2K′
(d) 2K = K′

Question. For which of the following reactions K310/K300 would be maximum?
(a) A + B → C; Ea = 50 kJ
(b) X + Y → Z; Ea = 40 kJ
(c) P + Q → R; Ea = 60 kJ
(d) E + F → G; Ea = 100 kJ

Question. For decomposition of N2O5(g) dissolved in CCl4 2N2O5(g)→ 4NO2(g) + O2(g)  B
The following data at 300 K is given   (Image 244)

The rate equation for the reaction is
(a) rate = K[N₂O₅]2
(b) rate = K[N₂O₅]
(c) rate = K[N₂O₅]₃
(d) rate = K[N₂O₅]0

Question. The half life period of the first order reaction PCl5 → PCl3 + Cl2 is 10 min. The time in which the concentration of PCl5 would be reduced to 10% of the original concentration will be
(a) 26 minutes
(b) 33 minutes
(c) 71 minutes
(d) 90 minutes

Question. For a zero order reaction, the plot of concentration Vs time is linear with
(a) +ve slope and zero intercept
(b) –ve slope and zero intercept
(c) +ve slop and non zero intercept
(d) –ve slop and non zero intercept

Question. The rate constant of forward and backward reactions for certain hypothetical reaction are 1.1 × 10^–2 and 1.5 × 10^–3 respectively. The equilibrium constant for the reaction is
(a) 7.33
(b) 0.733
(c) 73.3
(d) 733

Question. In the first order reaction the concentration of reactant decreases from 2 M to 0.50 M in 20 minutes. The value of specific rate constant is
(a) 69.32 min–1
(b) 6.932 min–1
(c) 0.6932 min–1
(d) 0.06932 min–1

Question. The rate of gaseous reaction is given by the expression K[A]2 [B]3. The volume of reaction vessel is suddenly reduced to one half of the initial volume. The reaction rate relative to the original rate will be
(a) 1/24
(b) 1/32
(c) 32
(d) 24

Question. Which of the following reactions ends in finite time?
(a) Zero order
(b) 1st order
(c) 2nd order
(d) 3rd order

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

Question. The rate of disappearance of AB3(g) in the reaction 2AB3(g)
K1 ⇋/K2 A2(g) + 3B2(g) would be
(a) 2K1 [AB3]2 – 2K2 [A2] [B2]3
(b) 2K1 [AB3] – K2 [A2] [B2]3
(c) K1 [AB3]2 – 2K2 [A2] [B2]3
(d) K1 [AB3] – K2 [A2] [B2]3

Question. For any hypothetical reaction 2A + 3B + C → Products    (Image 244) Order of the reaction is
(a) 3
(b) 4
(c) 2
(d) 1.5

Question. For the decomposition of N₂O₅ at 200ºC,
N₂O₅(g) → N₂O₄ (g) + 1/2 O₂ (g)
If the initial pressure is 114 mm and after 25 minutes of the reaction, total pressure of the gaseous mixture is 133 mm, the average rate of reaction in atm. min–1 will be
(a) 0.001 atm min^–1
(b) 0.002 atm min^–1
(c) 0.003 atm min^–1
(d) 0.004 atm min^–1

Question. A chemical reaction 2A → 4B + C in gas phase occurs in a closed vessel. The concentration of B is found to be increased by 5 × 10^–3 mol L^–1 in 10 seconds. The rate of disappearance of A will be
(a) 5 × 10^–4 mol L^–1 s^–1
(b) 10^–3 mol L^–1 s^–1
(c) 2.5 × 10^–4 mol L^–1 s^–1
(d) 1.25 × 10^–4 mol L^–1 s^–1

Question. The inversion of cane sugar proceeds with half life of 600 minutes at pH = 5 for any concentration of sugar.
However if pH = 6, the half life changes to 60 minutes.
The rate law expression for sugar inversion can be written as
(a) r = K[sugar]2 [H+]0
(b) r = K[sugar]1 [H+]0
(c) r = K[sugar]1 [H+]1
(d) r = K[sugar]0 [H+]1

Question. A gaseous reaction,  (Image 244) shows increase in pressure from 200 mm to 250 mm in 10 minutes. The rate of disappearance of A2 is
(a) 10 mm min–1
(b) 20 mm min–1
(c) 50 mm min–1
(d) 100 mm min–1

Question. The rate law for a reaction is found to be rate = K[NO₂ ^–] [I–] [H+]2 How would the rate of reaction change when, concentration of each of NO2 –, I– and H+ are tripled?
(a) 27 times
(b) 39 times
(c) 8 times
(d) 81 times

Question. The rates of a reaction starting with initial concentrations of 2 × 10^–3 M and 1 × 10^–3 M are equal to 2.40 × 10^–4 Ms^–1 and 0.60 × 10^–4 Ms^–1 respectively. The order of the reaction with respect to the reactant is
(a) 1
(b) 2
(c) 3
(d) 1.5

Question. The three-fourth of a first order reaction is completed in 32 minutes. What is the half-life period of the reaction?
(a) 8 min
(b) 16 min
(c) 4 min
(d) 64 min

Question. In a reaction, 5 g ethylacetate is hydrolysed per litrein t he presence of dil. HCl in 300 minutes. If the reaction is of first order and the initial concentration of ethyl acetate is 20 g/L, calculate the rate constant of the reaction [log2 = 0.301, log3 = 0.477]
(a) 3.2 × 10^–4 min^–1
(b) 1.6 × 10^–4 min^–1
(c) 9.6 × 10^–4 min^–1
(d) 4.3 × 10^–2 min^–1

Question. For a reaction, the energy of activation is zero. What is the value of rate constant at 300 K, if K = 1.6 × 106 s^–1 at 280 K?
(a) 3.2 × 106 s^–1
(b) 1.6 × 106 s^–1
(c) 4.8 × 106 s^–1
(d) 6.4 × 106 s–1s^–1

Question. For a first order reaction, time taken for half-life of the reaction to complete is t1, whereas that for 3/4th of the reaction to complete is t2. How are t1 and t2 related to each other?
(a) t₂ = 2t₁
(b) 2t₂ = t₁
(c) t₂ × t₁ = 1
(d) t₂ = t₁

Question. The rate of a gaseous reaction is halved when the volume of the vessel is doubled. The order of the reaction is
(a) 1
(b) 2
(c) 3
(d) Zero

Question. The decomposition of NH3 on platinum surface follows zero order kinetics with rate constant k=2.5×10–4Ms–1. The rate of production of N2 is
(a) 1.25 × 10^–4 Ms^–1
(b) 3.75 × 10^–4 Ms^–1
(c) 2.5 × 10^–4 Ms^–1
(d) 15 × 10^–4 Ms^–1

Question. Two first order reactions proceed at the same rate at 25ºC, when started with same initial concentrations.
The temperature coefficient of the first reaction is 2 while that of the second reaction is 3. What will be the ratio of the rates of the second reaction to the first at 55ºC?
(a) 27/8
(b) 9/8
(c) 81/8
(d) 1 : 1

Question. For a zero order reaction, starting with initial concentration Co, how long will it take for the reaction to go to completion?
(a) Co/2K
(b) Infinite
(c) Co/K
(d) Co

Question. A first order reaction is 40% complete in 50 minutes. In what time will the reaction be 80% complete?
(a) 105.2 min
(b) 97.4 min
(c) 157.5 min
(d) 50 min

Question. The half-life period of a first order reaction is 60 minutes. What percentage of the reactant will be left behind after 120 minutes?
(a) 25%
(b) 50%
(c) 75%
(d) 100%

Question. A substance undergoes first order decomposition as follows  (Image 246)
K1 : K2 = 3 : 5
Then % distribution of B and C are
(a) 37.5% B and 62.5% C
(b) 30% B and 70% C
(c) 40% B and 60% C
(d) 20% B and 80% C