Question

Class 12 Chemistry  MCQ Questions of Chemical Kinetics with Answers?

Answer 1

Solving the Chemical Kinetics Multiple Choice Questions of Class 12 Chemistry can be of extreme help as you will be aware of all the concepts. Have a learn the MCQ Questions for class 12 and cross-check your answers during preparation. Students are advised to practice the MCQ Questions for Class 12 Chemistry Chemical Kinetics with Answers free is available here. MCQ Questions for Class 12 Chemistry with Answers are prepared as per the Latest Exam Pattern and syllabus.

Students can solve these Class 12 MCQ Questions with Answers and assess their preparation level. These MCQ Questions of Chemical Kinetics Class 12 with answers for a quick revision of the Chapter thereby helping you to enhance subject knowledge.

Practice MCQ Question for Class 12 Chemistry chapter-wise

1. In chemical equation H₂ (g) + I₂ (g) ⇌ 2HI (g) the equilibrium constant K_p depends on

(a) total pressure
(b) catalyst used
(c) amount of H₂ and I₂
(d) temperature

2. A reaction in which reactants (R) are converted into products (P) follows second order kinetics. If concentration of R is increased by four times, what will be the increase in the rate of formation of P?

(a) 9 times
(b) 4 times
(c) 16 times
(d) 8 times

3. The rate constant of a reaction depends upon

(a) temperature of the reaction
(b) extent of the reaction
(c) initial concentration of the reactants
(d) the time of completion of reaction

4. 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

5.  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) molecuiarity of a reaction
(c) fast step of the mechanism of a reaction
(d) half-life of the reaction

6. 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) molecularity of the reaction can be determined only experimentally
(d) more than one reacting species are involved in one step

7. The overall rate of a reaction is governed 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

8. Half life period of a first order reaction is 10 min. What percentage of the reaction will be completed in 100 min?

(a) 25%
(b) 50%
(c) 99.9%
(d) 75%

9. 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 reactant is present in excess
(d) one of the reactant is non-reactive

10. Radioactive disintegration is an example of

(a) zero order reaction
(b) first order reaction
(c) second order reaction
(d) third order reaction

11. A plot of log (a – x) against time t is a straight line. This indicates that the reaction is of

(a) zero order
(b) first order
(c) second order
(d) third order

12. Rate of which reaction increases with temperature?

(a) Exothermic reaction
(b) Endothermic reaction
(c) (a) and (b) both
(d) None of the above

13. The activation energy in a chemical reaction is defined as

(a) the difference in energies of reactants and products
(b) the sum of energies of reactants and products
(c) the difference in energy of intermediate complex with the average energy of reactants and products
(d) the difference in energy of intermediate complex and the average energy of reactant

14. The rate of a chemical reaction tells us about

(a) the reactants taking part in reaction
(b) the products formed in the reaction
(c) how slow or fast the reaction is taking place
(d) none of the above

15. In the rate equation, when the concentration of reactants is unity then rate is equal to

(a) specific rate constant
(b)average rate constant
(c) stantaneous rate constant
(d))None of the above

16. The role of a catalyst is to change

(a) gibbs energy of reaction
(b) enthalpy of reaction
(c) activation energy of reaction
(d) equilibrium constant

17. The value of rate constant of a pseudo first order reaction ......................

(a) depends on the concentration of reactants present in small amount
(b) depends on the concentration of reactants present in excess
(c) is independent of the concentration of reactants
(d) depends only on temperature

18. Rate of reaction is inversely proportional to time. So it decreases with time. In a slow reaction, rate of reaction generally .......... with time:

(a) decreases
(b) increases
(c) sometimes increases and sometimes decreases.
(d) remains constant

19. Instantaneous rate of a chemical reaction is

(a) rate of reaction in the beginning
(b) rate of reaction at the end
(c) rate of reaction at a given instant
(d) rate of reaction between two specific time intervals

20. Order of reaction can be

(a) 0
(b) fraction
(c) whole number
(d) integer, fraction, zero

21. Velocity constant k of a reaction is affected by

(a) change in the concentration of the reactant
(b) change of temperature
(c) change in the concentration of the product
(d) None of the above

22. If the rate of a gaseous reaction is independent of pressure, the order of reaction is:

(a) 0
(b) 1
(c) 2
(d) 3

23. In a reaction, when the concentration of reactant is increased two times, the increase in rate of reaction was four times. Order of reaction is  

(a) zero
(b) 1
(c) 2
(d) 3

24. If concentration of reactants is increased by 'X', the rate constant K becomes:

(a) eK/X
(b) K/X
(c) K
(d) X/K

25. The decomposition of phosphine (PH₃) on tungsten at low pressure is a first-order reaction. It is because the

(a) rate is proportional to the surface coverage
(b) rate is inversely proportional to the surface coverage
(c) rate is independent of the surface coverage
(d) rate of decomposition is very slow

Answer 2

1. Answer : (d) temperature

Explanation: For the reaction, H₂(g) +I₂(g) ⇌2HI(g), the number of moles of gaseous reactants is equal to the number of moles of gaseous products. The equilibrium constant K_p is independent of 

(i) Total pressure
(ii) Catalyst

2. Answer : (c) 16 times

Explanation: 

For the reaction:

R → P

For a second order reaction, rate = k[R]²

If conc of R is increased by four times, rate = k[4R]²

=16k[R]²

Hence, the rate of formation of P increases by 16 times.

3. Answer : (a) temperature of the reaction

Explanation: Rate constant of a reaction depends on its temperature only and not affected by concentration.

4. Answer : (a) zero order reaction

Explanation: For a zero order reaction, rate = k[A]⁰ = k

Units = mol L ⁻¹time⁻¹.

5. Answer : (b) molecuiarity of a reaction

Explanation: Single step reaction is an elementary and in elementary reaction its molecularity is equal to the number of molecules taking part in a reaction.

6. Answer : (a) the order and molecularity of the slowest step are equal to one

Explanation: For a unimolecular reaction, both order and molecularity are one in the rate determining step.

7. Answer : (d) the rate of slowest intermediate step

Explanation: The reaction mechanism is the step-by-step process by which reactants actually become products. The overall reaction rate depends almost entirely on the rate of the slowest step. If the first step is the slowest, and the entire reaction must wait for it, then it is the rate-determining step.

8. Answer :(c) 99.9%

Explanation: 

 \(\frac{0.693}{t_{1/2}}\) \(=\frac{2.303}{t}log(\frac{a}{a-x})\)

 \(\frac{0.693}{t_{1/2}}\) \(=\frac{2.303}{100}log(\frac{100}{100-x})\)

\(\Rightarrow x=99.9\%\)

9. Answer : (c) one of the reactant is present in excess

Explanation: The reactions having molecularity two but the order of reaction is one is called pseudo unimolecular reactions, in such type of reactions, one reagent is take in the excess amount so that the disappearance of that reagent is negligible and it does not determine the rate of reaction. Example: Hydrolysis of ester CH₃COOC₂H₅ , Hydrolysis of sucrose.

10. Answer : (b) first order reaction

Explanation: rate of radioactive decay is directly proportional to the number of nuclei present in the sample. indicates that radioactive decay is constant. here from rate equation, it is clear that radioactive decay is a first-order reaction.

11. Answer : (b) first order

Explanation: First order reaction gives a straight line plot of log(a−x) and time. The Integrated rate law for the first order reaction is given as-

\(k=\frac{2.303}{t}log\frac{a}{a-x}\)

12. Answer : (c) (a) and (b) both

Explanation: Increase in temperature generally lowers the activation energy of the reaction.
Increasing the temperature will not always increase the rate of the reaction. If the temperature of a reaction were to reach a certain point where the reactant will begin to degrade, it will decrease the rate of the reaction.

13. ​Answer : (d) the difference in energy of intermediate complex and the average energy of reactant

Explanation: Activation energy is defined as the minimum amount of extra energy required by a reacting molecule to get converted into a product. It can also be described as the minimum amount of energy needed to activate or energize molecules or atoms so that they can undergo a chemical reaction or transformation.

14. ​Answer : (c) how slow or fast the reaction is taking place

Explanation: the speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or the concentration of a reactant that is consumed in a unit of time.

15. ​Answer : (a) specific rate constant

Explanation: Rate is equal to the rate constant of reaction when concentration of the reactant in unity. Thus rate constant is also known as specific reaction rate. Where all the terms have usual meaning. If CA = CB =1 then r = k .

16. ​Answer : (c) activation energy of reaction

Explanation: The role of a catalyst is to change the activation energy of reaction. This is done by either increasing or decreasing activation energy of molecule as catalyst are mainly of two types: + ve catalyst and − ve catalyst.

17. ​Answer : (b) depends on the concentration of reactants present in excess

Explanation: The value of the rate constant of pseudo-first-order reaction depends on the concentration of reactants present in excess amount.

18. ​Answer : (a) decreases

Explanation: Rate of reaction is inversely proportional to time.So it decreases with time.

19. ​Answer : (c) rate of reaction at a given instant

Explanation: The instantaneous rate of reaction is the rate at some instant at a particular time. it is defined as the change in concentration of the components of a reaction at an infinitely small time interval.

20. ​Answer : (d) integer, fraction, zero

Explanation: Order of reaction is equal to the number of molecules whose concentration is changing with time. It can be zero or in fractions or an integer.

21. ​Answer : (b) change of temperature

Explanation: Velocity constant ‘K’ is characteristic constant of a reaction and depends only on temperature.

22. ​Answer : (a) 0

Explanation: According to  zero-order reaction, when rate of reaction does not depend upon the partial pressure or concentration of reactants, then order of reaction is zero.

23. ​Answer : (c) 2

Explanation: In a reaction, when the concentration of reactant is increased  two times, the increase in rate of reaction was four times. Since rate of reaction becomes four times on doubling concentration of reactant, it is second order reaction.

24. Answer : (c) K

Explanation: Rate Constant doesn't depend on the concentration of the reactants. So, If the conc of reactants is increased by a factor x, then the rate constant k becomes k.

25. ​Answer : (a) rate is proportional to the surface coverage

Explanation: The decomposition of PH₃ on tungsten at low pressure is a first order reaction because surface area coverage is proportional to partial pressure of PH₃.

 Click here for MCQ Question for Chemical Kinetics Class 12