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Equilibrium is a state in chemical reactions in which there is no net change in the concentrations of the products as well as the reactants.
Examples of Chemical Equilibrium
In a chemical reaction, the reactants change into products. After the reaction starts, the rate of the backward and forward reactions may be similar. The reactants that were converted are again made by a reverse reaction.
As a result, the products and the reactants are in chemical equilibrium:
H2 + N2 ⇌ 2NH3
PCl2 + PCl3 ⇌ PCl5
2NO2 ⇌ N2O4
What is an Equilibrium reaction?
An equilibrium reaction refers to the chemical reaction between the reactants before and after the reaction is complete (i.e., a thermodynamic equilibrium state). An example of an equilibrium reaction is water evaporating to form vapour.
A thermodynamic equilibrium state refers to a reaction that satisfies all types of equilibrium.
These are as follows:
Thermal equilibrium
Chemical equilibrium
Mechanical equilibrium
Chemical Equilibrium
Chemical equilibrium is the state of a system where the concentration of the product and the reactant do not alter with time or show any additional changes in their properties.
Classifications of Chemical Equilibrium
There are two categories of chemical equilibrium:
Homogeneous equilibrium
Heterogeneous equilibrium
Homogeneous Equilibrium
When all the products and reactants of the chemical equilibrium are in a similar phase, it is known as homogeneous equilibrium. Moreover, there are two types of homogeneous equilibrium:
Reactions in which the amount of molecules in the reactants is equal to the number of molecules in the products. For example: O2 (g) + N2 (g) ⇌ 2NO (g)
Reactions in which the total amount of reactant molecules is not equal to the number of molecules in the products. For example: Cl2 (g) + CO (g) ⇌ COCl2(g)
Heterogeneous Equilibrium
When the products and reactants of chemical equilibrium are present in different phases, it is known as heterogeneous equilibrium. For example:
CO2 (g) + CaO (s)⇌CaCO3 (s)
Hence, the various types of chemical equilibrium are based on the phases of the products and the reactants.
Factors Affecting Chemical Equilibrium
Various factors such as pressure, concentration and temperature of the system affect chemical equilibrium:
1. Change in Concentration:
The concentration of the products or reactants added is controlled by the reaction which absorbs the added substance.
The concentration of the products or reactants eliminated is reduced by the reaction that is in the direction of restoring the substance removed.
When the concentration of the products or reactants is altered, there is a modification in the composition of the combination in the chemical equilibrium.
2. Change in Pressure:
A change in pressure due to modification in volume influences the gaseous reaction, since the total quantity of the gaseous products and reactants become varied.
3. Change in Temperature:
The impact of temperature on chemical equilibrium relies upon the sign of ΔH of the reaction and follows Le-Chatelier’s principle.
As the temperature boosts, the equilibrium constant of an exothermic reaction lessens.
The equilibrium constant rises with a rise in temperature in an endothermic reaction.
4. Effect of a Catalyst:
A catalyst only speeds up a reaction and does not influence the chemical equilibrium. It equally speeds up both the reverse and the forward reactions. This influences the reaction to attain its equilibrium faster.
In a catalysed and uncatalysed reaction the same number of products and reactants are present at equilibrium. The presence of a catalyst only stimulates the reaction to proceed through a low-energy transition state of reactants to products.
Conclusion
In this article, we have discussed the concept of equilibrium and equilibrium reactions as well as their classifications. We learned that equilibrium refers to a state in chemistry that shows no net change in the concentrations of the products or the reactants. Moreover, an equilibrium reaction is a chemical reaction between the reactants before and after the reaction is complete (i.e., a thermodynamic equilibrium state). An example of an equilibrium reaction is evaporation of water to form vapour. We also discussed the concept of chemical equilibrium and the factors that affect chemical equilibrium.
