Equilibrium Class 11 Notes

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Equilibrium Class 11

Equilibrium is an important topic in the class 11 chemistry syllabus and can also be a very scoring one if you study properly and all your concepts are clear. It is a vast chapter and contains many significant concepts such as buffer solutions, equilibrium constants, and many more. Here, through this blog, we have provided you with notes related to Equilibrium class 11 and cleared all your doubts. 

Must Read: Class 11 Hydrogen Notes


Before we go into further details in the equilibrium class 11 chapter, we must know what exactly is equilibrium. Equilibrium is reached when the molecules departing the liquid and entering the vapor are comparable to the molecules entering the liquid from the vapor. Kc is the equilibrium constant. It is calculated by dividing the concentration of products by the concentration of reactants and increasing each term to the stoichiometric coefficient.

At equilibrium, Rate of the forward reaction = Rate of the backward reaction

which is rf = RB Or, if × α × [A]a[B]b =  kb × α × [C]c [D]d

where rf = rate of forwarding reaction

What is Chemical Equilibrium?

Chemical Equilibrium is essential in many biochemical processes and the environmental system. For example, balancing involves O2 molecules and protein hemoglobin which also play an important role in the transportation of O2 from our body to the lung muscles. Related balances of CO molecules and hemoglobin are responsible for the degradation of CO. Remember this definition in the Equilibrium Class 11 notes which are important. 

Characteristics of Chemical Equilibrium:

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

Also Read: Chemical Bonding and Molecular Structure Class 11 Study Notes

Law of Chemical Equilibrium

In equilibrium class 11, we move on to the Law of Chemical Equilibrium. According to the Law of Chemical Equilibrium, the rate of a chemical reaction at constant temperature is directly proportional to the molar concentration of the reactants, which are each increased to a power equal to the respective stoichiometric coefficients defined by the balanced chemical equation. For example:

Equilibrium Class 11 - Laws of Chemical Equilibrium
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Types of Chemical Equilibrium

Class 11 of Equilibrium discusses the numerous types of chemical equilibrium. These are the two types of chemical equilibrium at action here, which are known as:

  • Homogeneous Equilibrium
  • Heterogeneous Equilibrium

Homogeneous Chemical Equilibrium 

In Homogeneous Equilibrium, the reagents and the chemical balance products are all in the same process. Homogenous balance can be further classified into two types: reactions in which the number of molecules of the compounds is equal to the number of molecules of the reactants. For instance, 

H2 (g) + I2 (g) 2HI (g) 

N2 (g) + O2 (g) No 2NO (g)

Heterogeneous Chemical Equilibrium 

In Heterogeneous Equilibrium, the reagents and chemical balance products are present in various phases. Here is an instance of heterogeneous equilibrium. 

CO2 (g) + C(s) No 2CO (g)

Equilibrium Constant and Gibbs Free Energy Relationship

The pace of a reaction has no effect on its equilibrium constant.

  • The change in Gibbs free energy G is negative, the reaction continues spontaneously in the forward direction.
  • If the change in Gibbs free energy G is positive, the forward reaction products must undergo a non-spontaneous transformation to reactants.
  • The change in Gibbs free energy is zero, the reaction is in equilibrium, and no more free energy is available to drive it.

Reversible and Irreversible Reactions

Because the reactants and products are not totally consumed in a chemical reaction, the process continues. Furthermore, simultaneous reactions occur in which reactants continue to create products while the latter reacts to produce reactants.

In the case of irreversible reactions, on the other hand, the products can never react again to generate reactants.

What is the Difference Between Chemical and Dynamic Equilibrium?

Next in equilibrium class 11 is the other name of chemical equilibrium, which is a dynamic equilibrium. The point at which the rate of forwarding reaction is equal to the rate of backward reaction is considered the level of equilibrium. At this point, the number of reagent molecules that transform into products or product molecules into reagents will be the same. The very same equilibrium can be performed with the same reagents everywhere under identical conditions with a continuous molecular exchange, hence the chemical equilibrium is dynamic.

Importance of Chemical Equilibrium 

Equilibrium class 11 talks about the importance of chemical equilibrium. It is useful in many manufacturing processes, such as 

  • Preparation of ammonia by Haber’s process: in this nitrogen it mixes with hydrogen to produce ammonia, the production of ammonia is higher at low temperature, high pressure and in the presence of iron as a catalyst. 
  • Preparation of sulphuric acid by contact process: the basic mechanism in this method is the transformation of sulphur dioxide into sulphur trioxide. This requires chemical equilibrium.

Characteristics of Equilibrium Involving Physical Processes  

Here are some of the characteristics of Equilibria that involve physical processes which is an important topic for Equilibrium Class 11:

  • Given at a temperature, only closed systems can maintain equilibrium. At equilibrium, the system’s observable properties stay steady.Balance is complex, as both forward and backward processes operate at the same time. 
  • At equilibrium, concentrations of compounds become stable at constant temperatures. 
  • The duration of the mechanism before achieving equilibrium determines the quality of the stable equilibrium.

Le Chatelier’s Principle 

It implies that the change of some factors, such as concentration, strain, temperature, etc., causes the balance to move in that direction to offset or decrease the influence of the change. The following are the impacts that he describes:

  • Effects of changes in concentration 
  • Effect of Volume Transition, Pressure 
  • Effects of variations in temperature 
  • Effect of Catalyst 

As variables such as concentration, pressure, temperature, inert gases, which influence balance, change, the balance shifts in that direction where even the effects induced by these changes are nullified. 


Electrolytes are compounds that conduct electricity in watery solutions. They include bases, salts, and acids. In an aqueous solution, cations and anions produced by the ionization or dissociation of electrolytes induce electricity.

Explore: Structure of Atom Class 11 Notes

We hope that our Equilibrium Class 11 notes were helpful for your learning and assist you in acing your exams. Check out our page, Leverage Edu for more Class 11 Notes on various subjects to help you in scoring great marks!

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