Chemical Kinetics - Notes, Topics, Formula, Books, FAQs

“You can’t cross the sea merely by standing and staring at the water.” – Tagore

Chemical kinetics is the branch of chemistry which deals majorly with the rates of chemical reactions. There are many reactions which occur instantaneously like AgNO₃ with HCl to form a salt i.e, AgCl while there are many reactions which occur too slow like the conversion of diamond into graphite. Along with feasibility, there are various other factors like rate and other parameters which control the rate of reactions. Chemical kinetics consider into account of all such types of reactions and tell us about their rate and the order of these reactions. In this chapter, you will learn about the rates and order of the reactions, Arrhenius equation, collision theory of reactions, etc.

In everyday life, there are various important chemical reactions which occur around us as follows:

• Role of chemical kinetics in the "refrigerator": We keep our food items in the refrigerator because it lowers the temperature of these substances. As the temperature is lowered, the reaction rates are low and thus the food items can be used for longer times.

  

• Role of chemical kinetics in the making of "popcorn": Each popcorn kernel contains little amount of water in them. Now when the popcorn kernels are heated, then the water turns into the vapour which tries to come out of the kernel shell. Due to this heating and vapourisation, as the pressure is further is increased, the kernel shells are burst out with a 'pop' sound.

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• In chemical kinetics, you also learn about how on changing the reaction conditions like temperature and pressure, the rate of reaction changes. It also gives you information about the reaction mechanisms, activation energy and reaction intermediates.

• Notes for Chemical Kinetics

  In this section, you will study about the important topics of the chapter, overview, formulae and some important tips and guidelines for the preparation of the chapter at the best.

  Important Topics of Chemical Kinetics

• Rate of chemical reaction
• Factors influencing the rate of reaction
• Order of a reaction
• Zero-order reactions
• First order reactions
• Second order reactions
• Pseudo first order reactions
• Arrhenius equation, Activation energy and its determination
• Collision theory of reactions

Overview of the Chemical Kinetics

(i) Rate of reaction: Similar to any object moving with a certain velocity, chemical reactions also occur with certain velocities also known as the rate of reaction. This rate of reaction is defined as how fast the product is forming or how fast the reactants are getting consumed with respect to time. Mathematically, it can be expressed as follows:

(ii) Rate expression and rate constant: For the general reaction:

The rate equation is given as follows:

This equation can be written as follows:

where x and y may or may not be stoichiometric coefficients. The addition of these components (x+y) gives the order of the reaction.

(iii) Order of the reaction: The rate equation of a chemical reaction is given as:

where (x+y) gives the order of the reaction and k is the rate constant.

• Units of rate constant: For a general reaction:
  
  
  
  
  The unit of rate constant (k) depends on the order of the reaction i.e. (x+y).

  Reaction type	Order of reaction	Units of rate constant
  Zero-order reaction	0	mol L-1 s-1
  First order reaction	1	s1
  Second order reaction	2	mol-1L s-1

NCERT Notes Subject Wise Link:

• NCERT notes Class 11 Maths
• NCERT notes Class 11 Physics
• NCERT notes Class 11 Chemistry
• NCERT notes Class 11 Biology

Zero-order reaction: It is the type of reaction, where the order of reaction is proportional to the zero power of the concentration of reactants. The rate equation is given as follows:

• First order reaction: In these type of reactions, the rate of reaction is proportional to the first power of the concentration of reactants. The rate equation is given as follows:
  

• The half-life of reaction: It is the time at which the concentration of reactant is half of its initial value. It is denoted by t_1/2. Mathematically, it can be described as follows:

• 

  • Arrhenius Equation: The rate of a chemical reaction depends on the temperature. For every 10⁰ rise in temperature, the rate constant gets doubled. This temperature dependency of the rate of chemical reaction is explained by the Arrhenius equation as given below:
    k = A e^-E_a/RT
    where A is the Arrhenius factor, E_a is the activation energy and R is the gas constant
    

  • Collision Theory of Chemical Reactions: This theory gives a deeper insight into the mechanism of the chemical reactions. According to this theory, the reactant molecules are considered to be spherical molecules and the reaction occurs when these spherical molecules collide with each other. Mathematically, it can be described as follows:
    Rate = Z_AB e^E_a/RT
    where Z_AB is the collision frequency. The number of collisions per second per unit volume of the reaction mixture is known as "collision frequency(Z)".

• How to prepare for Chemical Kinetics?

  • This chapter is a part of physical chemistry. There are some simple formulas and equations like zero order reaction, first-order reaction, etc. which you must understand completely because these concepts are the root of this chapter.

  • Before reading this chapter, first, you must have the basic knowledge of the mole concept.

  • You must deeply observe how the graphs show some trends, how to find the rate constants from the graphs, how to find the order of the reactions, etc.

  • Rest this chapter is very simple, just be regular and be consistent in your numerical practice.

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• NCERT Solutions Subject wise link:

  • NCERT solutions for class 11 Physics.
  • NCERT solutions for class 11 Chemistry.
  • NCERT solutions for class 11 Mathematics.
  • NCERT solutions for class 11 Biology.

• NCERT Exemplar Solutions Subject wise link:

  • NCERT exemplar solutions for class 11 Physics.
  • NCERT exemplar solutions for class 11 Chemistry.
  • NCERT exemplar solutions for class 11 Mathematics.
  • NCERT exemplar solutions for class 11 Biology.

• Prescribed Books for Chemical Kinetics

First, you must finish the class XII NCERT book and solve each and every example and unsolved question given in it. Then for advanced level preparation like JEE and NEET, you must follow R.C. Mukherjee and O.P. Tandon. You must definitely solve the previous year papers. Meanwhile, in the preparation, you must continuously write the mock tests for the depth of knowledge. This article will help you to provide with the variety of questions for deeper knowledge with the help of videos, articles and mock tests.