Equilibrium in Chemical Process: Definition, Types, Factors, & Class 11 Notes

A state in a chemical reaction where the rate of the forward and reverse reaction is equal is called chemical equilibrium. At this point, the concentration of reactants and products remains constant over time.  

Example: $\mathrm{a}\mathrm{A}+\mathrm{b}\mathrm{B}\rightleftharpoons \mathrm{c}\mathrm{C}+\mathrm{d}\mathrm{D}$

Chemical Equilibrium Key Features

1. Equilibrium occurs in a reversible reaction.
2. The system seems to be stable, but the reaction continues at equal rates in both directions.
3. Equilibrium can be dynamic, which means the molecules are reacting, yet no overall changes are observed.

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Chemical equilibrium is a state where forward and reverse reactions are equal and the concentration of reactants and products is constant over time. Depending on the nature of substances involved and the phase of the system, types of chemical equilibrium are categorized.

Types of Chemical Equilibrium

1. Homogeneous Equilibrium: In the homogeneous equilibrium, all the reactants and products are usually in the same phase. 
$N_2\left(g\right)+3H_2\left(g\right)\rightleftharpoons 2{\mathrm{NH}}_3\left(g\right)$ (Haber process).
2. Heterogeneous Equilibrium:  In the heterogeneous equilibrium, both reactants and products are in different phases.

${\mathrm{CaCO}}_3\left(s\right)\rightleftharpoons \mathrm{CaO}\left(s\right)+{\mathrm{CO}}_2\left(g\right)$

Chemical equilibrium position can be affected by the change in external conditions such as temperature, volume, concentration, pressure, and catalyst. These changes are capable of shifting the balance toward either the reactants or the products. As per Le Chatelier's Principle, a system will adjust itself to counter any changes imposed on it. 

Also Read: NCERT Solutions | Class 11 Chemistry NCERT Solutions

 Factors Affecting Chemical Equilibrium

1. Concentration: Adding reactants or products to the system will shift the equilibrium to reduce the change. Example: Adding a reactant shifts the equilibrium to form more products. 

2. Temperature: An Increase in temperature favours the endothermic direction, and a decrease in temperature favours the exothermic direction.
3. Pressure (for gas): An Increase in pressure shifts the equilibrium towards fewer gas molecules, and a decrease in pressure shifts the equilibrium to more gas molecules.
4. Catalyst: It speeds up the rate of forward and reverse reactions equally. The position of equilibrium is not shifted.
5. Volume ( related to gases): A change in volume affects the pressure, which indirectly shifts the equilibrium depending on the number of molecules. 

Here we have mentioned a few points on the importance of chemical equilibrium.
1. Haber's Process: In this process, ammonia is prepared by combining nitrogen with hydrogen. At relatively low temperature, high pressure, and the presence of iron as a catalyst, the yield of ammonia is high.
2. Contact Process: In this process, oxidation of sulphur dioxide into sulphur trioxide is the fundamental reaction involving chemical equilibrium. 

The key characteristics of equilibrium in chemical processes are mentioned below: 
1. It is dynamic in nature
2. The rate of forward and reverse reactions is equal.
3. The concentration of reactants and products remains constant over time.
4. Equilibrium occurs in a reversible reaction only.
5. Equilibrium is affected by external conditions such as temperature, concentration, or pressure.

Read: Class 11 Chemistry Equilibrium NCERT Notes