Law of Chemical Equilibrium Numericals for JEE

When observable parameters like colour, temperature, pressure, concentration, etc., do not change, the process is said to be in equilibrium. As "balancing" is the meaning of the word "equilibrium," it follows that a chemical reaction represents a balance between the reactants and products involved in the reaction. In some physical processes, such as the melting of ice at 0°C, where both ice and water are at equilibrium, the equilibrium state can also be observed.

Physical equilibrium refers to the equilibrium that results from physical processes like the melting of solids, salt dissolving in water, etc. Chemical equilibrium refers to the equilibrium that results from chemical reactions.

Chemical Reaction Equilibrium

When a system is in a state of chemical equilibrium, neither the reactant concentration nor the product concentration changes over time, and the system's properties are not changing any further.

Rate of Reaction v/s Time

When the rate of the forward reaction equals the rate of the reverse reaction, the system is said to have reached chemical equilibrium. The system is considered to be in a dynamic state of equilibrium when the concentrations of the reactants and products do not change further due to the equal rates of the forward and reverse reactions at that moment.

Characteristics of Equilibrium States

1. Only when a reversible reaction is carried out in a closed environment can equilibrium be reached.

2. The constancy of specific attributes, such as pressure, concentration, density, or colour, indicates chemical equilibrium at a certain temperature.

3. When we start the reaction, the reactants or the products have no bearing on the concentration of each reactant and product at equilibrium.

4. A positive catalyst is used to achieve equilibrium in less time.

5. Its nature is dynamic. However, since the concentration of the reactants and products remains constant, the reaction appears to have stopped.

Chemical Equilibrium Examples

In chemical reactions, the forward reaction transforms reactants into products, and the backward reaction transforms products into reactants. Reactants and products are two separate compositional states.

The pace of the forward and backward reactions may become equal after some time has passed since the reaction began. Following this, the number of reactants converted will be generated once more by the reverse reaction, preventing any further changes in the concentration of reactants and products. Therefore, there is a chemical balance between the reactants and products.

• ${{N}_{2}}{{O}_{4}}\rightleftharpoons 2N{{O}_{2}}$ 

• $PC{{l}_{5}}\rightleftharpoons PC{{l}_{3}}+PC{{l}_{2}}$ 

• ${{N}_{2}}+{{3H}_{2}}\rightleftharpoons 2N{{H}_{3}}$ 

Types of Chemical Equilibrium

Two different types of chemical equilibrium exist:

1. Homogeneous Equilibrium

2. Heterogeneous Equilibrium

Homogeneous Chemical Equilibrium

This type has all of the reactants and chemical equilibrium products in the same phase. Further categorisation of homogeneous equilibria yields two categories: reactions in which the total number of molecules in the reactants and products is the same and reactions when the total number of reactant molecules is greater than the total number of result molecules.

For example, ${{H}_{2}}(g)+{{I}_{2}}(g)\rightleftharpoons 2HI(g)$ 

Heterogeneous Chemical Equilibrium

This class contains the reactants and products of chemical equilibrium in various phases. Thus, the phases of the reactants and products determine the different types of chemical equilibrium.

For example, $C{{O}_{2}}(g)+C(s)\rightleftharpoons 2CO(g)$ 

Law of Chemical Equilibrium

According to the "Law of Chemical Equilibrium," the equilibrium constant is the ratio of the product of the concentration of the products to the product of the concentration of the reactants. Each concentration term raises the stoichiometric coefficient in the balanced chemical equation. This ratio is known as the equilibrium constant when the temperature remains constant.

For the reaction:

$aA(aq)+bB(aq)\rightleftharpoons cC(aq)+dD(aq)$ 

At equilibrium,

$\Rightarrow {{K}_{eq}}={{K}_{c}}=\dfrac{{{[C]}^{c}}{{[D]}^{d}}}{{{[A]}^{a}}{{[B]}^{b}}}$

Where ${{K}_{c}}=\frac{{{k}_{f}}}{{{k}_{b}}}$ and square brackets $[ \ ]$ is used to indicate “molar concentration”.

Chemical Equilibrium Equation

For the reaction:

$aA(g)+bB(g)\rightleftharpoons cC(g)+dD(g)$ 

The equilibrium constant in terms of concentration:

${{K}_{c}}=\dfrac{{{k}_{f}}}{{{k}_{b}}}=\dfrac{{{[C]}^{c}}{{[D]}^{d}}}{{{[A]}^{a}}{{[B]}^{b}}}$ 

The equilibrium constant in terms of partial pressure:

${{K}_{p}}=\dfrac{{{{{p}_{C}}}^{c}}{{{{p}_{D}}}^{d}}}{{{{{p}_{A}}}^{a}}{{{{p}_{B}}}^{b}}}$ 

Relation between ${{K}_{P}}$ and ${{K}_{C}}$

${{K}_{p}}={{K}_{c}}{{(RT)}^{\Delta n}}$ 

Here,${\Delta n}$ is the difference in the number of gas molecules on the product side and reactant side.

Conclusion

In conclusion, we have learnt that when the quantifiable attributes, such as pressure, density, colour, or concentration of a system do not change noticeably over time under a specific set of circumstances, it is considered to be in equilibrium. In case of chemical equilibrium, neither the reactant concentration nor the product concentration changes over time, nor does the system exhibit any further changes in its attributes. 

When the rate of the forward reaction equals the rate of the reverse reaction, it is considered as chemical equilibrium. Only when reversible reaction is carried out in a closed environment, equilibrium can be reached. A positive catalyst is used to achieve equilibrium in less time. Its nature is dynamic. The concentration of the reactants and products, however, remains unchanged, giving the reaction the appearance of having stopped.