Short Answer

Chemical equilibrium is a state in a reversible reaction where the forward and backward reaction rates become equal. At this point, the concentrations of reactants and products remain constant, even though both reactions continue to occur. It does not mean the reaction has stopped; it only means the system has reached a balance.

Chemical equilibrium is dynamic because particles keep reacting, but there is no overall change in concentration. This balance is very important in chemistry because it helps predict the final composition of a reaction mixture and understand how different conditions affect the reaction.

Detailed Explanation :

Chemical Equilibrium

Chemical equilibrium is an important concept in chemistry that describes the balanced state of a reversible reaction. Many reactions do not go to completion; instead, they reach a condition where both reactants and products exist in measurable amounts. When the rate of the forward reaction becomes equal to the rate of the backward reaction, the reaction is said to be in equilibrium. This balance allows the system to remain stable over time.

Chemical equilibrium is not a static condition. It is dynamic, meaning reactant molecules continue to form products, and product molecules continue to form reactants. However, these two processes occur at the same rate, so there is no overall change in the amount of reactants or products. This dynamic balance is essential for understanding natural processes, industrial reactions, and biological systems.

1. Forward and Backward Reactions

In a reversible reaction, the reactants form products, and the products can convert back into reactants.

1. a) Forward Reaction

Reactants → Products
This reaction continues until enough product accumulates.

1. b) Backward Reaction

Products → Reactants
As more product forms, the backward reaction rate increases.

Reaching Equilibrium

Eventually, both reactions occur at the same rate.
At this point:

• Concentrations become constant
• No net change occurs
• Reaction appears to stop, but it continues at the molecular level

2. Dynamic Nature of Chemical Equilibrium

Equilibrium is not still or inactive. It is dynamic because:

• Molecules keep reacting
• New bonds form and old bonds break
• Overall concentrations stay the same

Even though nothing seems to change when a reaction is at equilibrium, continuous activity is happening inside the system.

3. Conditions Required for Equilibrium

For chemical equilibrium to occur:

• The reaction must be reversible
• The system must be closed (no substances added or removed)
• Temperature and pressure must remain constant

If any of these conditions change, the equilibrium position will shift.

4. Equilibrium Constant (K)

At equilibrium, the ratio of the concentration of products to reactants remains constant.
This constant value is known as the equilibrium constant (K).

For a reaction:
aA + bB ⇌ cC + dD

K = [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ

Meaning of K

• High K value → products are favoured
• Low K value → reactants are favoured

The equilibrium constant helps predict how far a reaction will proceed.

5. Factors Affecting Chemical Equilibrium (Brief Explanation)

Although the main question is about equilibrium, it is useful to understand that:

1. a) Concentration

Adding more reactant or product shifts equilibrium to restore balance.

1. b) Temperature

Increasing or decreasing heat shifts the equilibrium position depending on whether the reaction is endothermic or exothermic.

1. c) Pressure (for gases)

Changing pressure affects reactions involving gases.

1. d) Catalyst

A catalyst speeds up both forward and backward reactions equally but does not change the equilibrium position.

These factors help maintain or shift equilibrium in different conditions.

6. Examples of Chemical Equilibrium
7. a) Haber Process

N₂ + 3H₂ ⇌ 2NH₃
Used in ammonia production; equilibrium is controlled by temperature and pressure.

1. b) Water Ionization

H₂O ⇌ H⁺ + OH⁻
This natural equilibrium helps maintain pH balance.

1. c) Carbonic Acid System in the Body

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
Important for maintaining blood pH.

These examples show that equilibrium plays a role in industries and living organisms.

7. Characteristics of Chemical Equilibrium

• It is dynamic, not static.
• Concentrations remain constant but reactions continue.
• Can only occur in closed systems.
• Forward and backward reaction rates are equal.
• The equilibrium constant is fixed at a given temperature.

These characteristics help identify and study equilibrium systems.

Conclusion

Chemical equilibrium is the balanced state of a reversible reaction where the forward and backward reaction rates become equal. At equilibrium, the concentrations of reactants and products remain constant, although both reactions continue. This dynamic balance is essential in chemistry, industry, and biology because it helps predict reaction behaviour and control reaction outcomes. Understanding chemical equilibrium allows chemists to optimize conditions for maximum efficiency and stability in various processes.