CBSE Class 12 Chemistry Chemical Kinetics Worksheet Set B

Question. The rate law for a reaction,
A + B → C + D is given by the expression k[A].
The rate of reaction will be
(a) doubled on doubling the concentration of B
(b) halved on reducing the concentration of A to half
(c) decreased on increasing the temperature of the reaction
(d) unaffected by any change in concentration or temperature.
Answer. b

Question. For a general reaction X Y, the plot of conc. of X vs time is given in the figure. What is the order of the reaction and what are the units of rate constant?
(a) Zero, mol L^–1 s^–1
(b) First, mol L^–1 s^–1
(c) First, s^–1
(d) Zero, L mol^–1 s^–1
Answer. a

Question. Radioactive disintegration is an example of
(a) zero order reaction
(b) first order reaction
(c) second order reaction
(d) third order reaction.
Answer. b

Question. When a chemical reaction takes place,during the course of the reaction the rate of reaction
(a) keeps on increasing with time
(b) remains constant with time
(c) keeps on decreasing with time
(d) shows irregular trend with time.
Answer. c

Question. In a reaction 2HI → H₂ + I₂, the concentration of HI decreases from 0.5 mol L^–1 to 0.4 mol L^–1 in 10 minutes. What is the rate of reaction during this interval?
(a) 5 × 10^–3 M min^–1
(b) 2.5 × 10^–3 M min^–1
(c) 5 × 10^–2 M min^–1
(d) 2.5 × 10^–2 M min^–1
Answer. a

Question. Consider the reaction, 2N₂O₅ → 4NO₂ + O₂.In the reaction NO₂ is being formed at the rate of 0.0125 mol L^–1 s^–1. What is the rate of reaction at this time?
(a) 0.0018 mol L^–1 s^–1
(b) 0.0031 mol L^–1 s^–1
(c) 0.0041 mol L^–1 s^–1
(d) 0.050 mol L^–1 s^–1
Answer. b

Question. The rate constant of a first order reaction is 15 × 10^–3 s^–1. How long will 5.0 g of this reactant take to reduce to 3.0 g?
(a) 34.07 s
(b) 7.57 s
(c) 10.10 s
(d) 15 s
Answer. a

Question. Which of the following statements for order of reaction is not correct?
(a) Order can be determined experimentally.
(b) Order of reaction is equal to the sum of powers of concentration terms in rate law expression.
(c) Order cannot be fractional.
(d) Order is not affected by stoichiometric coefficient of the reactants.
Answer. c

Question. For a reaction R → P, the concentration of a reactant changes from 0.05 M to 0.04 M in 30 minutes. What will be the average rate of reaction in minutes?
(a) 4 × 10^–4 M min^–1
(b) 8 × 10^–4 M min^–1
(c) 3.3 ×10^–4 M min^–1
(d) 2.2 × 10^–4 M min^–1
Answer. c

Question. For the reaction 4NH₃ + 5O₂ → 4NO + 6H₂O,if the rate of disappearance of NH₃ is 3.6 × 10^–3 mol L^–1 s^–1, what is the rate of formation of H₂O?
(a) 5.4 × 10^–3 mol L^–1 s^–1
(b) 3.6 × 10^–3 mol L^–1 s^–1
(c) 4 × 10^–4 mol L^–1 s^–1
(d) 0.6 × 10^–4 mol L^–1 s^–1 
Answer. a

Question. The half-life of the reaction X → Y, following first order kinetics, when the initial concentration of A is 0.01 mol L^–1 and initial rate is 0.00352 mol L^–1 min^–1 will be
(a) 19.69 min
(b) 1.969 min
(c) 7.75 min
(d) 77.5 min
Answer. b

Question. The rate of a gaseous reaction is given by the expression k[A]²[B]³. The volume of the reaction vessel is reduced to one half of the initial volume.
What will be the reaction rate as compared to the original rate a?
(a) 1/8 a
(b) 1/2 a
(c) 2a
(d) 32a
Answer. d

Question. In pseudo unimolecular reactions,
(a) both the reactants are present in low concentration
(b) both the reactants are present in same concentration
(c) one of the reactants is present in excess
(d) one of the reactants is non-reactive
Answer. c

Question. Nitrogen dioxide (NO₂) dissociates into nitric oxide (NO) and oxygen (O₂) as follows:
2NO₂ → 2NO + O₂
If the rate of decrease of concentration of NO₂ is 6.0 × 10^–12 mol L^–1 s^–1, what will be the rate of increase of concentration of O₂?
(a) 3 × 10^–12 mol L^–1 s^–1
(b) 6 × 10^–12 mol L^–1 s^–1
(c) 1 × 10^–12 mol L^–1 s^–1
(d) 1.5 × 10^–12 mol L^–1 s^–1
Answer. a

Question. The reaction 2X → Y + Z would be zero order reaction when
(a) rate remains unchanged at any concentration of Y and Z
(b) rate of reaction doubles if concentration of Y is doubled.
(c) rate of reaction remains same at any concentration of X
(d) rate of reaction is directly proportional to square of concentration of X.
Answer. c

Question. For a unimolecular reaction,
(a) the order and molecularity of the slowest step are equal to one
(b) molecularity of the reaction can be zero, one or two
(c) more than one reacting species are involved in one step
(d) molecularity of the reaction can be determined only experimentally.
Answer. a

Question. For a reaction P + Q → 2R + S. Which of the following statements is incorrect?
(a) Rate of disappearance of P = Rate of appearance of S
(b) Rate of disappearance of Q = 2 × Rate of appearance of R
(c) Rate of disappearance of P = Rate of disappearance of Q
(d) Rate of disappearance of Q = 1/2 × Rate of appearance of R
Answer. b

Question. The rate constant for the reaction,
2N₂O₅ → 4NO₂ + O₂ is 2 × 10^–5 s^–1. If rate of reaction is 1.4 × 10^–5 mol L^–1 s^–1, what will be the concentration of N₂O₅ in mol L^–1?
(a) 0.8
(b) 0.7
(c) 1.2
(d) 1
Answer. b

Question. The number of molecules of the reactants taking part in a single step of the reaction is indicative of
(a) order of a reaction
(b) molecularity of a reaction
(c) fast step of the mechanism of a reaction
(d) half-life of the reaction.
Answer. b

Question. Which of the following is an example of a fractional order reaction?
(a) NH₄NO₂ → N₂ + 2H₂O
(b) NO + O₃ → NO₂ + O₂
(c) 2NO + Br₂ → 2NOBr
(d) CH₃CHO → CH₄ + CO
Answer. d

Question. The unit of rate and rate constant are same for a
(a) zero order reaction
(b) first order reaction
(c) second order reaction
(d) third order reaction.
Answer. a

Question. The value of rate of a pseudo first order reaction depends upon
(a) the concentration of both the reactants present in the reaction
(b) the concentration of the reactant present in small amount
(c) the concentration of the reactant present in excess
(d) the value of DH of the reaction.
Answer. b

Question. In a reaction 2X → Y, the concentration of X decreases from 3.0 moles/litre to 2.0 moles/litre in 5 minutes. The rate of reaction is
(a) 0.1 mol L^–1 min^–1
(b) 5 mol L^–1 min^–1
(c) 1 mol L^–1 min^–1
(d) 0.5 mol L^–1 min^–1
Answer. a

Question. The decomposition of dimethyl ether is a fractional order reaction. The rate of reaction is given by rate = k(pCH₃COCH₃)^3/2. If the pressure is measured in bar and time in minutes, then what are the units of rate and rate constant respectively?
(a) bar min^–1, bar² min^–1
(b) bar min^–1, bar^–1/2 min^–1
(c) bar^–1/2 min^–1, bar² min^–1
(d) bar min^–1, bar^1/2 min^–1
Answer. b

Question. The chemical reaction, 2O₃ → 3O₂ proceeds as
O₃ ⇌ O₂ + [O] (fast)
[O] + O₃ → 2O₂ (slow)
The rate law expression will be
(a) Rate = k[O][O₃]
(b) Rate = k[O₃]² [O₂]^–1
(c) Rate = k[O₃]²
(d) Rate = k[O₂][O]
Answer. b

SHORT ANSWER TYPE QUESTIONS 

Question. Time for half change for a first order reaction is 25 min. What time will be required for 99% reaction ?
Answer. 166.16 mins.

Question. 4NH₃ + 5O₂ → 4NO + 6H₂O. If rate of formation of NO is 6 × 10⁻⁴ atm min^-1, calculate the rate of formation of H₂O.
Answer. 9.0 × 10⁻⁴ atm min^-1

Question. A first order reaction has a rate constant 1.15 × 10^-3 s^-1. How long will 5 gram of this reactant take to reduce to 3 grams ?
Answer. t = 444 seconds

Question. The half life period of a first order reaction is 60 min. What % will be left after 240 mins. ?
Answer. 6.25%

Question. Consider a certain reaction A → Product with K = 2.0 × 10^-2 s^-1. Calculate the concentration of A remaining after 100 s, if the initial concentration of A is 1.0 mol L^-1.
Answer. [A] = 0.135 M

Question. The conversion of the molecules X to Y follows second order kinetics. If the concentration of X is increased to three times, how will it affect the rate of formation of Y ?
Answer. 9 times

Question. Write the difference between order and molecularity of reaction.
Answer.
Order Molecularity
1. It is the sum of the powers of concentration 1. It is the number of reacting species undergoing  terms in the rate law expression. simultaneously collision in a reaction.
2. It is determined experimentally. 2. It is a theoretical concept.
3. Order of reaction need not to be a whole num 3. It is whole number only. ber.
4. Order of reaction can be zero. 4. It can’t be zero or fractional.