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NCERT Class 11 Chemistry Chapter 7 Notes Equilibrium - Download PDF

NCERT Class 11 Chemistry Chapter 7 Notes Equilibrium - Download PDF

Edited By Sumit Saini | Updated on Apr 09, 2024 02:55 PM IST

Chemical equilibrium refers to a state in which neither the reactants nor the products can alter any further. In this situation, the forward and backward reaction rates stay constant. For students to grasp advanced concepts, the concept of equilibrium becomes crucial. Equilibrium class 11 notes are important from the exam perspective as many questions are asked from Chemical equilibrium in JEE Mains and NEET examination. By referring to cbse class 11 chemistry ch 7 notes, students can gain a deeper understanding of equilibrium reactions, Le Chatelier's principle, and factors affecting equilibrium.

Notes for Class 11 Chemistry chapter 7 provide a detailed study of the topic. Students should keep an eye out for all key facts while studying the topic. Such ideas are necessary, especially for the many chemical equations that a student would encounter. Class 11 Chemistry chapter 7 notes are designed using the most recent NCERT Syllabus and CBSE guidelines. Students can turn to the following resources for extra information on any topic covered in this chapter.

Also, students can refer,

NCERT Class 11 Chemistry Chapter 7 Notes

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 1

Types of Equilibrium

Equilibrium is a state in which the forces on both sides are equal. It is a moment in a chemical reaction where the rate of forward reaction equals the rate of backward reaction, according to chemistry. Or, to look at it another way, it is the state in which the concentrations of reactants and products are equal.

  • Equilibrium in the physical process

All physical processes attain this when all state variables such as pressure, temperature, and so on become constant. There are three types of this.

1. Solid-liquid equilibrium

Ice and water are in equilibrium at a specific temperature and pressure. The temperature at which the solid and liquid phases of any pure substance are in equilibrium at atmospheric pressure is known as the normal melting point or normal freezing point of the substance. When the system is in dynamic equilibrium, the following conditions will implement ,

Both opposing processes occur at the same time.

Because both processes happen at the same time, the volume of ice and water stays the same.

2. Liquid-vapour equilibrium

H2O(l) ⇔ H2O(vap)

This reaction shows the conversion of water to vapour.The number of water molecules that pass from the gaseous to the liquid state increases until equilibrium is established.

rate of evaporation = rate of condensation

The constant temperature at which the vapour pressure of a liquid equals atmospheric pressure is known as the boiling point. Temperature is the state variable that becomes constant.

3. Solid-vapour equilibrium

I2(solid) ⇔ I2(vapour)

Camphor(solid) ⇔ Camphor(vapour)

NH4Cl(solid) ⇔ NH4Cl(vapour)

At equilibrium Rate of solidification = Rate of evaporation

4. Equilibrium involving dissolution of solids or liquids in gases

Dissolution occurs when a solid dissolves in a liquid. The forward reaction is dissolution in this case. When the solvent is unable to dissolve any more solute, crystallization occurs in a reverse reaction. At equilibrium the rate of dissolution equals the rate of crystallization. Concentration is the state variable that remains constant.

General characteristics of physical equilibrium

  • The properties that can be measured become constant.

  • It can only be accomplished in a closed vessel.

  • The opposing forces become equal at equilibrium.

  • The concentration is constant at equilibrium.

  • The magnitude of the equilibrium value indicates the reaction's extent.

  • The equilibrium is dynamic. That is, the reaction continues, but the rate remains constant.

  • Equilibrium in chemical process

Chemical reactions, like physical systems, reach a point of equilibrium. Those chemical processes can take place both forward and backward. When the rate of forward reaction equals the rate of backward reaction, the chemical equilibrium is dynamic in nature.

Reversible reactions

A+B ⇔ C+D

With the passage of time, the concentrations of reactants A and B decline while the concentrations of products C and D increase, resulting in a decrease in forward reaction and an increase in backward reaction rates. The system will attain equilibrium when the two reactions occur at the same pace.

Irreversible reactions

A+B yields→ C+D

The irreversible reaction occurs when the products generated do not react again to form reactants under the same conditions. It is impossible for these reactions to occur in the opposite direction.

Characteristics of chemical equilibrium

  • At equilibrium, the concentrations of each of the reactants and products become constant.

  • At equilibrium, the rate of forwarding reaction equals the rate of backward reaction, implying that equilibrium is dynamic.

  • Only chemical equilibrium can be achieved if none of the products are permitted to escape or separate as a solid.

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 2

Equilibrium Constant

A reactant and product mixture in equilibrium is referred to as an equilibrium mixture.Consider the following reversible reaction:

A+B ⇔ C+D


Where Kc is called equilibrium constant and it’s unit is mol/L.

The product of reaction product concentrations raised to their separate stoichiometric coefficients in the balanced chemical equation divided by the product of reactant concentrations raised to their individual stoichiometric coefficients has a constant value at a given temperature. This is Equilibrium Law, sometimes known as the Law of Chemical Equilibrium.

For the reaction

a A+ b B ⇔ cC+dD


The ratio of the concentration of products to the concentration of reactants is defined as the equilibrium constant of a chemical reaction at equilibrium.


  • The value of the equilibrium constant for a given reaction is always constant, regardless of the concentrations of the reactants with which we begin or the direction from which the equilibrium was approached.

  • If “K” is the equilibrium constant, then the equilibrium constant of the reversed reaction is given by 1/K.

  • Let K is the equilibrium constant.If the equation is divided by 2 the equilibrium constant will changed to K.

  • Let K is the equilibrium constant.If the equation is multiplied by 2 the equilibrium constant will changed to K2

  • The value of the equilibrium will not be affected by adding a catalyst to the reaction.

Applications of equilibrium constant

  • Predicting the extent of reaction

The equilibrium constant is related to the extent of reaction

The reaction moves forward if the value of k is large.

If the value of k is less than one, the reaction is in backward direction.

If k>103, the extent is considerable in this case, and the reaction is practically complete.

If k is less than 10-3, the reaction will proceed to a lesser extent.

There is a significant concentration of reactants and products if the value of k is between 10-3and 103

  • Predicting the direction of the reaction

It indicates whether the reaction is going in the direction of the product or reactant. Q is the reaction quotient.

Reactants predominate if Q<k.

Reaction is at equilibrium if Q=k.

Products predominate if Q>k.

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 3

Homogeneous and Heterogeneous Equilibria

Homogeneous equilibrium

A homogenous system is an equilibrium system in which all of the reactants and products are in the same phase.

N2+3H2(g) ⇔ 2NH3(g)

Heterogeneous equilibrium

Heterogeneous equilibrium refers to an equilibrium system with many phases. The equilibrium between water vapour and liquid water in a closed container is a well-known example of this type of system.

H2O(l) ⇔ H2O(vap)

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 4

Equilibrium Constant in Gaseous State

Partial pressures are useful for gaseous processes because partial pressure is directly proportional to concentration at any fixed temperature. In the case of a typical gaseous reaction

a A+ b B ⇔ cC+dD


Relationship between Kc and Kp

PV = nRT



For the reaction

H2+I2 ⇔ 2HI


Putting values Kp=[CHIRT]2/[CHRT][CIRT]

=[CHI]2/[CHCI] RT(2-2)

Ie Kp=Kc(RT)∆ng

Where ng denotes the change in number of gaseous moles

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 5

Relationship Between Equilibrium Constant and Gibbs Free Energy

The value of a reaction's equilibrium constant is independent of the rate of reaction. If the change in Gibbs free energy ΔG is negative, the reaction proceeds spontaneously in the forward direction. If the change in Gibbs free energy ΔG is positive, the forward reaction products must be transformed to reactants through a non-spontaneous mechanism. If the change in Gibbs free energy is zero, the reaction is in equilibrium, and no more free energy is available to drive it.

∆G=∆G0+RTln Q

Here Go represent the standard Gibbs free energy.Equilibrium condition gives

Go=0 and Kc=Qc

∆G=∆G0+RTln Kc =0

Go=- RT ln Kc

ln Kc =-∆G0RT


NCERT Class 11 Chemistry Chapter 7 Notes: Topic 6

Factors Affecting Equilibria

Le Chatelier’s principle

This principle helps in examining the reaction's progress and making a qualitative prediction about how changes in conditions will affect equilibrium. It states that " If an equilibrium is subjected to a change of concentration, pressure or temperature, the equilibrium shifts in the direction that trends to undo the effect of the change". This principle is applicable to all physical and chemical systems .

Effect of concentration change

The addition or removal of any reactant or product, in general, disturbs equilibrium. According to Le Chatelier's principle, the direction of the net reaction that consumes the added substance reduces the concentration of the added reactant or product. "When the concentration of any of the reactants or products in an equilibrium reaction is changed, the equilibrium mixture's composition changes to minimize the influence of concentration variations."

Effect of temperature change

If there is a change in temperature there is a change in equilibrium constant. The sign of the ΔH for the reaction affects the temperature change dependency of the equilibrium constant. If ΔH is negative, the exothermic reaction's equilibrium constant decreases as the temperature rises. If ΔH is positive, the endothermic reaction's equilibrium constant increases as the temperature falls.

Effect of pressure change

A pressure change generated by changing the volume might impact the yield of products in a gaseous reaction when the total number of moles of gaseous products is different. The principle of Le-Chatlier is applied to heterogeneous equilibrium.Change in volume of solids and liquids on the application of pressure is very less so here the effect of pressure change on solids and liquids can be neglected.

Effect of volume change

The effect of a pressure rise is the same as the effect of a volume drop.As a result, the effect of a drop in volume will be moved towards equilibrium in the direction of a decrease in number of moles.

Effect of catalyst

A catalyst is the chemical substance that increases the rate of a chemical reaction by opening up a new low-energy pathway for reactants to become products.The rate of forward and reverse reactions that pass through the transition state is increased by a catalyst, but the equilibrium is not affected.

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 7

Ionic Equilibria in Solution

The following is an example of an equilibrium reaction involving ions

Fe+3+SCN- ⇔ [Fe(SCN)]2+(aq)

Based on their ability to conduct electricity, Micheal Faraday divided the substances into two categories, electrolytes and non-electrolytes. The electrolyte solution conducts electricity due to the presence of ions. An aqueous solution of NaCl, for example, is totally dissociated into Na+ and Cl-ions due nearly 100 percent ionization. In the instance of acetic acid, which is a weak electrolyte, ionization occurs to the extent of 5%. In weak electrolytes, equilibrium is thus created between ions and unionized molecules. Ionic Equilibrium is a type of equilibrium involving ions in an aqueous solution.

Strong electrolytes are electrolytes that are quickly broken into ions with complete dissociation. Weak electrolytes are electrolytes that have been partially dissociated into ions.

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 8

Acids, Bases, and Salts

The explanation of acids and bases has a variety of theories.

  • Arrehenius concept

According to this theory acids are substances that generate hydrogen ions when dissolved in water. Eg: HCl

It was later discovered that these hydrogen ions interact with water to create the hydronium ion. Bases are substances that release hydroxide ions when dissolved in water. Eg: NaOH

It was later discovered that just a few compounds do not release hydrogen or the hydroxide ion. However, they continue to behave as acids or bases. As a result, new theories were introduced.

  • Brönsted-Lowry theory

According to the Brönsted-Lowry theory, an acid is a substance that can donate a hydrogen ion, H+, while a base can take a hydrogen ion, H+. Proton donors are acids, whereas proton acceptors are bases.

H2O + NH3 ↔ NH4++ OH-

Lowry-Bronsted acid and Lowry-Bronsted base are water molecules that act as proton donors and ammonia molecules that act as proton acceptors respectively in this reaction.

  • Lewis concept

According to this concept, an acid is a species that accepts electron pairs whereas a base is a species that donates them.

Lewis acids: AlCl3,Co3+,Mg2+

Lewis bases: H2O, NH3, OH-

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 9

Ionic Product of Water

Water molecules, for example, have the unique ability to operate as both an acid and a base

H2O(l)acid+H2O(l)base ⇔ H3O+(aq)+OH-(aq)

The dissociation constant is given by the equation


Water's concentration is ignored in the denominator because it is a pure liquid with a constant concentration. The Ionic Product Of Water, Kw, is then equal to the equilibrium constant.


[H+] = 1.0 *10-7 M at 298 K

Dissociation of water molecule produce equal no of H+ and OH- ions


Kw=[H+][OH-] =(1*10-7)2=1*10-14M2

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 10

pH Scale

The pH scale is used to determine the nature of any substance. The negative logarithm of hydrogen ion concentration is used to calculate the pH of a solution.

pH =- log [H3O+]

The acidic or basic strength of a solution is measured by its pH

In pH scale upto 7 is acidic , at 7 it is neutral and above 7 it is basic.

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 11

Ionization of Acids and Bases

Dissociation constant of acids Ka


HA+H2O ↔ H3O+ + A-

Then K=H3O+ [A-]/HA[H2O]

K*[H2O]= H3O+[A-]/HA

Or Ka=H3O+[A-]/HA

Dissociation constant of bases Kb

BOH+H2O ↔ B++OH-

Then K=B+[OH-]/BOH[H2O]



The degree of dissociation (α)is the ratio of the number of dissociated molecules to the total number of molecules.

For acids

HA+H2O ↔ H3O++A-

Initial concentration c 0 0

At equilibrium c(1-α) c c


On putting values

Ka=c α.c αc(1-α)



For weak acids degree of dissociation is very less. So we can neglect in denominator.So for weak acids


Also pKa=-logKa

For bases

BOH+H2O ↔ B++OH-




As we know Ka. Kb=Kw

Then - logKa-log Kb=-logKw

pKa+ pKb=pKw

pKa+ pKb=14 at room temperature

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 12

Common ion Effect




On adding a substance that contain acetate ion, for example sodium acetate

CH3COONa ↔ CH3COO- + Na+

The process reverses direction due to an increase in acetate ions. That is, it prevents acetic acid from dissociating. This is referred to as the common ion effect.It can be defined as "the suppression of acid ionisation when a substance containing a common ion is added to it."

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 13

Buffer Solutions

Many physiological fluids, such as blood or urine, have a specific pH, and any variation from this shows that the body is malfunctioning. Controlling pH is also crucial in a variety of chemical and biological activities. Many medical and cosmetic compositions demand that they be stored and delivered at a specific temperature and a specific pH. Buffer Solutions are resistant solutions that resist pH change.

NCERT Class 11 Chemistry Chapter 7 Notes: Topic 14

Solubility Equilibrium For A Sparingly Soluble Salt

Each salt has a specific solubility that is affected by temperature. Salts are divided into three types based on their soluble properties.


Significance of NCERT Class 11 Chemistry Chapter 7 Notes

Equilibrium Class 11 notes gives an overview of the Class 11 chapter Equilibrium and is based on the latest NCERT syllabus. The goal of CBSE Class 11 Chemistry chapter 7 notes is to make the learning and revision process easier for students. NCERT notes for Class 11 Chemistry chapter 7 are very helpful for the preparation of competitive exams including NEET and JEE Main. For offline study students can use chemistry class 11 chapter 7 notes pdf download. Additionally, ch 7 chemistry class 11 notes offer detailed explanations and examples to help students grasp the underlying principles effectively. Students can use chemistry class 11 chapter 7 notes pdf download to obtain the notes and study offline.

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Frequently Asked Question (FAQs)

1. What is catalyst in Chemistry?

Ans: Class 11 Chemistry chapter 7 notes provide a definition of catalyst. It is a chemical that increases the rate of a reaction without changing the reaction itself. Sulphides, oxides, and halides of various metallic and semi-metallic elements, such as aluminium, boron, and silicon, are some of the most prevalent catalysts.  By referring to cbse class 11 chemistry ch 7 notes, students can gain a deeper understanding of catalysis in chemistry. 

2. What is Chemical equilibrium?

Ans-. When the rate of the forward reaction equals the rate of the reverse reaction, the reaction is said to be in chemical equilibrium. It is a condition in which both the reactant and the product are present in stable concentrations, resulting in no discernible changes in the system's properties. A bubbly cool drink, in which the carbon dioxide is dissolved in the liquid in the bottle, is an example of chemical equilibrium.

3. How do electrolytes conduct electric current?

Ans- Electrolytes are substances that help in the conduct of electric current by allowing ions to dissociate. Ions are positively and negatively charged particles that travel from the cathode to the anode terminals.

4. What is a heterogeneous equilibrium?

Ans- Reactants and products exist in two or more physical states or phases in heterogeneous equilibrium. further, ch 7 chemistry class 11 notes can be referred for deeper understanding on the topic of heterogeneous equilibrium. 

5. What is Reaction quotient ?

Ans- The ratio of the molar concentrations of the products to those of the reactants for any reversible reaction at any point other than equilibrium. The reaction quotient is the product of each concentration term being raised to the power of the stoichiometric coefficient for the substance in concern.


Get answers from students and experts

A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg


An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)


Option 2)

\; K\;

Option 3)


Option 4)


In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)


Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)


Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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