Course Content
Topic Name 10 Haloalkanes and Haloarenes 10.1 Classification 10.2 Nomenclature 10.3 Nature of C–X Bond 10.4 Methods of Preparation of Haloalkanes 10.5 Preparation of Haloarenes 10.6 Physical Properties 10.7 Chemical Reactions
Topic Name 11 Alcohols, Phenols and Ethers 11.1 Classification 11.2 Nomenclature 11.3 Structures of Functional Groups 11.4 Alcohols and Phenols 11.5 Some Commercially Important Alcohols 11.6 Ethers
Topic Name 13 Amines 13.1 Structure of Amines 13.2 Classification 13.3 Nomenclature 13.4 Preparation of Amines 13.5 Physical Properties 13.6 Chemical Reactions 13.7 Method of Preparation of Diazonium Salts 13.8 Physical Properties 13.9 Chemical Reactions 13.10 Importance of Diazonium Salts in Synthesis of Aromatic Compounds
Topic Name 14 Biomolecules 14.1 Carbohydrates 14.2 Proteins 14.3 Enzymes 14.4 Vitamins 14.5 Nucleic Acids 14.6 Hormones
Topic Name 15 Polymers 15.1 Classification of Polymers 15.2 Types of Polymerisation Reactions 15.3 Molecular Mass of Polymers 15.4 Biodegradable Polymers 15.5 Polymers of Commercial Importance
Topic Name 16 Chemistry in Everyday Life 16.1 Drugs and their Classification 16.2 Drug-Target Interaction 16.3 Therapeutic Action of Different Classes of Drugs 16.4 Chemicals in Food 16.5 Cleansing Agents
Class 12th Chemistry Online Class: Excelling in CBSE Board Exams
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Class 12th Chemistry Chapter 4 Chemical Kinetic


The stream of chemistry that governs the rate of reactions along with their mechanisms is termed as Chemical kinetics derived from a Greek word meaning chemical movement.

Combination of two or more reactants to produce a new product is called reaction.

Elementary Reaction:

The reaction that occurs in a single step to give the product is called an elementary reactions.

Complex reaction:

The reactions that occur as a result of sequence of elementary reactions to give the product is called complex reactions.    

Rate of reaction

The rate at which the concentration of reactant or product participating in a chemical reaction alters is called rate of reaction.

Rate of reaction = change in concentration/ time = (mol/litre)/time

Reactant (R) –> Product.

Rate [R]

Rate = k[R]

k = rate constant or velocity constant.

Let one mole of the reactant A produce one mole of the product B.

Let at time t1

[A]1 and [B]1 = Concentrations of A and B

Let at time t2

[R]2 and [P]2 =  Concentrations of A and B

Rate of disappearance of A = Decrease in concentration of R / Time taken = -∆[A]/∆t

Rate of appearance of B = Increase in concentration of P / Time taken = +∆[B]/∆t

When two or more reactants combine with each other the molecules of the respective reactants collide with each other to form the product. The collision between the molecules increases with the increase in concentration of the reactants and thereby increases the rate of reaction. A + B –> C + D

Chemical Kinetics

Here molecules of reactant A and B collide to produce molecules of product C and D.

Therefore we can conclude that rate of reaction is directly proportional to the concentration of the participating reactants.

Rate ∝ [A]x [B]y

Or Rate = k[A]x [B]y

Hg(l) + Cl2 (g) –> HgCl2(s)

Rate of reaction= -∆[Hg]/∆t = ∆[Cl2]/∆t = ∆[Hg Cl2]/∆t

Factors affecting rate of reaction

Nature of reactant

Nature of bonding in the reactants determines the rate of a reaction. The ionic compounds react faster compared to covalent compounds due to requirement of energy in covalent compounds to cleave the existing binds. 

The reaction between ionic compounds:

Precipitation of AgCl

AgNO3 + NaCl –> AgCl + NaNO3

The reactions between covalent compounds:


Rate of reaction increases with the rise in temperature due to increase in average kinetic energy which in turn increases the number of molecules having greater energy than threshold energy and consequently increasing the number of effective collisions. The rate of a reaction is doubled (i.e., increased by 100%) with 10 oC rise in temperature.


Increase in partial pressure increases the number of collisions. Therefore, the rate of reactions involving gaseous reactants increases with the increase in partial pressures.


 A catalyst increases the rate of reaction by giving an alternative path with lower activation energy (Ea’) for the reaction to proceed. 

Concentration of reactants

Increase in concentration increases the number of collisions and the activated collisions between the reactant molecules. According to the collision theory, rate is directly proportional to the collision frequency. Consequently, the rate of a reaction increases with the rise in the concentration of reactant.

Chemical Kinetics

Surface area

The rate of a reaction increases with increase in the surface area of solid reactant.

PROBLEM.   For the reaction: 2A + B → A2B  , The rate = k[A][B]2with k= 2.0 x 10-6mol-2L2s-1. Calculate the initial rate of the reaction when [A] = 0.1 mol L-1, [B] = 0.2 mol L-1. Calculate the rate of reaction after [A] is reduced to 0.06 mol L-1.

SOLUTION.   Rate = k [A][B]2

= (2.0 × 10 – 6mol – 2L2s – 1) (0.1 mol L – 1) (0.2 mol L – 1)2

= 8.0 × 10 – 9mol – 2L2s – 1

Reduction of [A] from 0.1 mol L – 1to 0.06 mol – 1

The concentration of A reacted = (0.1 – 0.06) mol L – 1 = 0.04 mol L – 1

The concentration of B reacted= 1/2 x 0.04 mol L-1 = 0.02 mol L – 1

The concentration of B available, [B] = (0.2 – 0.02) mol L – 1

= 0.18 mol L – 1

After reduction of [A] to 0.06 mol L – 1

The rate of the reaction

Rate = k [A][B]2

= (2.0 × 10 – 6mol – 2L2s – 1) (0.06 mol L – 1) (0.18 mol L – 1)2

= 3.89 mol L – 1s – 1

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