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NCERT Solutions for Class 12 Chemistry Chapter 4 – Chemical Kinetics

NCERT Solutions for Class 12 Chemistry Chapter 4 – Chemical Kinetics are meticulously prepared by best Chemistry experts. This chapter of NCERT Solutions tells you that chemical kinetics is a very important branch of Chemistry which deals with reactions mechanisms and the study of reaction rates. In this chapter you learn about average and instantaneous rates of reaction, expressing the reaction rate in terms of concentration change of the species involved, order and molecularity of reaction, and dependence of the rate of reaction on factors like a catalyst, temperature and concentration. You will also learn to define and determine rate constant and what is collision theory.

In this chapter, there are a total of 30 questions asked at the end. All of these questions are designed to cover all the concepts taught in NCERT CBSE Class 12 Chemistry Chapter 4. The questions given in the chapter enable you to have a thorough revision of the concepts learnt in chemical kinetics and its application.

All of these questions are answered comprehensively in Class 12 Chemistry Chapter 4 – Chemical Kinetics. They follow all the guidelines given by CBSE and NCERT. These are precise solutions that help you learn effectively.

NCERT Class 12 Chemistry Chapter 4: Important Topics

NCERT Solutions for Class 12 Chemistry Chapter 4 – Chemical Kinetics incorporates all the concepts of the unit. They give you an in-depth understanding of the subject matter. An overview of the concepts covered in this chapter are as follows –

  • Rate of a Chemical Reaction

This part of the chapter tells you that the rate of any reaction is a measurement of a decrease in the number of reactants or increase in the number of products per unit time. Instantaneous rate is expressed at a particular time, and the average rate of reaction is calculated over a large time period. General unit of rate of reaction is concentration time-1.

  • Factors Influencing Rate of Reaction

This part of the chapter tells you that the rate of reaction can be affected by a number of experimental conditions like temperature, the concentration of reactants (pressure in case of gases), and catalyst. Further, you learn about rate law here where the reaction rate is expressed in terms of the molar concentration of reactants. Each of the reactant terms is raised to some power that may or may not be equal to the stoichiometric coefficient of the reactants in the balanced chemical equation. 

  • Order of a reaction

This part of the CBSE NCERT Class 12 Chemistry Chapter 4 tells you that in a given rate equation, Rate = k [A]x [B]y, the sum of the exponents, x + y gives the overall order of the reaction and x and y represent the order of reactants A and B respectively. This part further tells you that the unit of zero-order reaction is mol L-1 s-1, the first-order reaction is s-1, and the second-order reaction is mol-1 L s-1.

  • Molecularity of a reaction

This part of the NCERT CBSE Class 12 Chemistry Chapter 4 lets you know about molecularity. Molecularity is the number of ions, atoms or molecules reacting in elementary reactions to bring about the chemical reaction while colliding with each other. Its values are limited from 1 to 3 whereas order can be 0, 1, 2, 3 or even a fraction.

  • Integrated Rate Equations

This part teaches you that differential equations of instantaneous rates can be integrated to give a relation between concentrations at different times and rate constant. The integrated rate equations are different for the reactions having different reaction orders. For zero-order reaction, Rate = k and plot of concentration of reactant versus time can be plotted where the slope of the straight line obtained is equal to –k

For first-order reactions rate equation is given as k = (2.303/t) log{[R]0/[R]} and if we plot ln[R] against t, we get a straight line with slope = –k and if we plot a graph between log[R]/[R]0 versus t the slope is k/2.303.

This part of the NCERT Class 12 Chemistry Chapter 4 further discusses half-life of a reaction which is the time in which the quantity of reacting species reduces to half of the initial quantity expressed as t1/2 = 0.693/k. For zero-order reactions, t1/2 is directly proportional to the initial concentration of reactant {[R]0}, and for the first-order reaction, t1/2 does not depend on [R]0.

  • Pseudo-first-order reactions

This part of the chapter tells you that when one of the participating reactants is in large excess, and it virtually does not affect the rate of reaction, then this type of reaction is called pseudo-first-order reaction.

  • Temperature dependence of the rate of a reaction

Here you learn that most of the chemical reactions are accelerated by a rise in temperature. You will also learn that experimentally it has been found that the rate constant is nearly doubled when the reaction temperature is increased by 10°C. 

The accurate explanation of temperature dependence is given by Arrhenius equation, k = A e-Ea/RT, where A is Arrhenius factor, Ea is the activation energy. Increasing the temperature of the reaction system increases the fraction of molecules colliding with energies greater than Ea, finally giving rise to products. 

This part further discusses the effect of a catalyst on a reaction. A catalyst is a substance which itself does not take part in the reaction but reduces activation energy to provide an alternate reaction mechanism. 

  • Collision Theory of Chemical Reactions

This portion of the NCERT Solutions for Chapter 4 – Chemical Kinetics tells you that according to collision theory steric factor, P is important and contributes to the effective collisions. Prefers to the orientation of molecules which collide to give successful reactions. It modifies the Arrhenius equation as follows –k = PZAB e-Ea/RT

CBSE NCERT Class 12 Chemistry Chapter 4 Exercise

Our NCERT Solutions for Chapter – ‘Chemical Kinetics’ consists of 30 questions covering the important topics learnt here. The components of the exercise have been listed below. 

  • Question 1 asks you to determine the order of the given reaction equations.
  • Questions 2 and 3 are numerical problems that ask you to calculate the rate of reactions.
  • Question 4 asks you to determine the rate constant and its unit. 
  • Questions 5 to 7 are direct questions based on factors affecting the rate of a chemical reaction.
  • Question 8 is a numerical asking to calculate the reaction rate and constant for the pseudo-first-order reaction. 
  • Question 9 asks you to tell how the rate is affected by the concentration change of reactant having different orders.
  • Question 10 is a numerical asking you to calculate the order of the reaction.
  • Question 11 is a numerical asking you to determine the rate law and rate constant.
  • Question 12 is a numerical problem and asks you to determine different parameters of a reaction utilizing the given data.
  • Questions 13 to 19 are numerical problems based on the concept of the half-life of a reaction. 
  • Questions 20 and 21 ask you to determine the rate constant and rate of reaction. 
  • Question 22 is a numerical asking you to determine reaction parameters.
  • Question 23 is a word problem asking you to calculate the pre-exponential factor.
  • Questions 24 and 25 are numerical problems that ask you to determine the remaining quantity of reactant.
  • Questions 26 to 29 are word problems based on the energy of activation. 

There are 9 intext questions asked in CBSE NCERT Class 12 Chemistry Chapter 4 to which elaborate and accurate answers are provided in our solutions.

Benefits of NCERT Solutions for Class 12th Chemistry Chapter 4 – Chemical Kinetics

Some of the major benefits of learning and revising from NCERT Solutions for Class 12 Chemistry Chapter 4 – Chemical Kinetics are as follows –

  • They cover the fundamental concepts of chemical kinetics thoroughly as this is a very important branch of physical Chemistry. 
  • They are concise, fully accurate and facilitate fast and effective learning.
  • They help you learn how to solve numerical from this chapter in a step by step manner so that you can fare well in your exams.
  • The solutions work as a ready reckoner of the topics covered in the chapter enabling you to score high in class 12th board exams. 
  • They have been strategically devised to help you prepare for both your board exams and other important competitive exams. 
  • They clear all your doubts and help you remember more.