MCQ on Chemical Kinetics

Chemical kinetics is an important topic in Physical Chemistry that helps students grasp the various components of a chemical reaction. More specifically, kinetics is concerned with the rate of change of a quantity. For example, velocity denotes the rate of change of displacement. Similarly, acceleration is the rate at which velocity changes.

Chemical reactions are typically characterized as rapid (e.g., Na + H₂O), moderate (Mg + H₂O), or slow (esterification) depending on this pace. In this post, we will learn more about chemical kinetics, explore how to calculate the pace of a reaction, and investigate numerous elements that influence the rate of a reaction.

Question 1.The equilibrium constant Kp in the chemical equation H₂ (g) + I₂ (g) →2HI (g) is determined by

 (a) total pressure,

 (b) catalyst utilized,

 (c) amount of H₂ and I₂,

 (d) temperature.

Answer

(b) the catalyst utilized

Question 2.If a reaction’s rate is represented as rate = A [A]² [B], the reaction’s order will be 

(a) 2

(b) 3

(c) 1

(d) 0.

Answer

(b) 3 

3.. A reaction’s rate constant is k=3.28 × 10^-4 s^-1. Determine the reaction’s order.

a) First order

b) Second order

c) Third order

d) Fourth order

Answer-:: a)first order   

Explanation: Given that k= 3.28 × 10^-4s^-1

The standard formula for calculating rate constant units is k=(mol L^-1)^1-ns^-1, where n is the order of the reaction. For (mol L^-1)^1-ns-1 to become s-1, the value of n must be 1. As a result, k=3.28 × 10^-4s^-1 denotes a first order reaction.

Question 4: Dimethyl ether breakdown is a fractional order process. rate =k(PCH₃OCH₃)^3/2 gives the rate. What are the units of rate and rate constant if pressure is measured in bars and time is measured in minutes? (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) bar min^-1 bar^1/2 min^-1

Question 4. The reaction NO₂ + CO → NO + CO₂ occurs in two steps. Locate the rate law.

2NO₂ → NO + NO₃ (k1) – slow

NO₃ + CO → CO₂ + NO₂ (k2) – fast

a) R = k1 [NO₂] ³

b) R = k2 [NO₃] [CO]

c) R = k1 [NO₂]

d) R = k1 [NO₂]²

Answer: d) R = k1 [NO₂]²

Explanation: In any reaction, the slowest step is the rate determining step; the overall reaction rate is determined by this step. As a result, the rate determining step is 2NO₂= NO + NO₃(k1). As a result, the rate rule R= k1[NO₂]² .

Question 6.Which of the following reactions 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)CH₃CHO → CH₄ + CO is the correct answer.

Question 7.The rate constant for the reaction 2H₂ + 2NO → 2H₂O + N₂ with rate = K|H₂||NO|², is 

(a) mol L^-1 s^-1

(b) s^-1

(c) mol^-2  L² s^-1

(d)mol L^-1

Answer: (c) mol^-2 L² s^-1

Question 8.. What is the rate law for acid hydrolysis of an ester in aqueous solution, such as CH₃COOC₂H₅?

a) k [CH₃COOC₂H₅]

b) k [CH₃COOC₂H₅] [H₂O]

c) k [CH₃COOC₂H₅]²

d) k

Answer-:

Explaination-: : Acid hydrolysis of ester, CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅OH

When one reactant is taken in excess of the other, the reaction’s sequence can be changed.

Water is present in excess according to the rate law R= k [CH₃COOC₂H₅] [H₂O].

As a result, R=k [CH₃COOC₂H₅]. 

Question 9. If the concentration of material X is doubled and that of Y is halved, how many times will the rate of the elementary reaction 3X + Y = X₂Y change?

a) r2= 4.5r1

b) r2= 5r1

c) r2= 2r1

d) r2= 4r1

Answer: d) r2= 4r1

Because it is an elementary reaction, the rate law r1= k [A]³[B]

The new rate will be r2=k when the concentrations are changed  

r2= k (2[A])3([B]/2) = 4k[A]³[B]

As a result, r2=4r1

Question 10.A reaction’s rate constant is determined by

 (a) temperature of the reaction

(b) extent of the reaction

(c) initial concentration of the reactants

(d) the time of completion of reaction

Answer: (d) the time of completion of reaction

Explanation-: The rate of reaction constant is determined by the time taken by the reaction is completed by time taken to completion of the whole reaction.

Question 11.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

Answer: (b) Rate = k [O₃]² [O₂]^-1

Question 12: For a given rate, the unit of rate and the rate constant are the same.

(a) zero order reaction

(b) first order reaction

(c) second order reaction

(d) third order reaction

Answer: (a) zero order reaction

Explanation-: A zero-order reaction is a chemical reaction in which the rate does not change when the concentration of the reactants increases or decreases. 

Question 13.The number of molecules of the reactants involved in a single stage of the reaction indicates

 (a) the order of the reaction

(b) the molecularity of the reaction

(c) the rapid step of the reaction mechanism, and 

(d) the reaction half-life.

Answer: (b) the molecularity of reaction

Explanation-: The total number of reacting species in a rate-determining step is known as the reaction’s molecularity.

Question 14.For a unimolecular reaction,

 (a) the slowest step’s order and molecularity are both one

(b) the reaction’s molecularity can be zero, one, or two;

 (c) the reaction’s molecularity can only be determined experimentally

  (d) more than one reacting species are engaged in one step.

Answer: (a) the slowest step’s order and molecularity are both one.

Explanation-: Unimolecular reactions are ones in which just one ionic structure molecule is changed. The molecule’s dissociation or isomerization might be considered typical examples of such reactions.

Question No. 15

The overall rate of a reaction is determined by

 (a) the rate of fastest intermediate step

(b) the sum total of the rates of all intermediate steps

(c) the average of the rates of all the intermediate steps

(d) the rate of slowest intermediate step

Answer: (d) the rate of slowest intermediate step

Question 16.The order of reactions is determined by 

(a) temperature,

 (b) reaction mechanism, and relative reactant concentrations,

(c) molecularity, and (d) pressure.

Answer

(b) reaction mechanism, and relative reactant concentrations

Question 17.In a first-order reaction, the rate constant is

 (a) inversely proportional to the concentration units

(b) independent of concentration units

(c) directly proportional to concentration units

(d) inversely proportional to the square of concentration units

Answer: (b) independent of concentration units

Question 18.A first order reaction has a half-life length of 10 minutes. In 100 minutes, what proportion of the response will be completed?

( a) 25%

(b) 50%

(c) 99.9%

(d) 75%

Answer

(c) 99.9%

Question 19.In pseudo unimolecular reactions, 

(a) both reactants are present in low concentrations, 

(b) both reactants are present in the same concentrations,

(c) one reactant is present in excess, 

 (d) one reactant is non-reactive.

Answer

(c) one reactant is present in excess,

Question 20.For a 30 percent breakdown, a first order reaction takes 40 minutes. What will t₁₂be? 

(a) 77.7 min

(b) 52.5 min

(c) 46.2 min

(d) 22.7 min

Answer: (a) 77.7 min

Question 21.The rate constant of a first order reaction is 1.15 10^-3s-1. How long will it take to decrease 5 g of this reactant to 3 g? 

 (a) 444 seconds

(b) 400 seconds

(c) 528 seconds

(d) 669 seconds

Answer

(a) 444 seconds

Question 22.An example of a zero order reaction is radioactive disintegration.

(a) zero order reaction

(b) first order reaction

(c) second order reaction

(d) third order reaction

Answer

Answer: (b) first order reaction

Question number 23.

A straight line is drawn when log (a – x) is plotted against time t. This shows that the response is of order

 (a) zero, (b) first, (c) second, and (d) third.

Answer

(b) first order 

Question 24.Which reaction’s rate increases as the temperature rises?

(a) Exothermic reaction

(b) Endothermic reaction

(c) (a) and (b) both

(d) None of the above

Answer

Answer: (c) (a) and (b) both

Question 25.In a chemical reaction, the activation energy is defined as

 (a) the difference between the energies of the reactants and products, and (b) the sum of the energies of the reactants and products.

(c) the difference between the average energy of reactants and products and the energy of the intermediate complex

(d) the difference between the energy of the intermediate complex and the average energy of the reactants

Answer

(d) the difference between the energy of the intermediate complex and the average energy of the reactants.