Grade 11 Chemistry Note (Ch 8)

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Easy Notes — Grade 11 Chemistry

Chapter 8 — Chemical Equilibrium

8.1 What is Chemical Equilibrium?

Chemical equilibrium is a state where:

  • forward reaction and backward reaction occur at the same rate

  • concentration of reactants and products remains constant

Example:

N2​+3H2​⇌2NH3​

At equilibrium:

  • ammonia is still being formed

  • ammonia is also decomposing

  • both happen equally

Characteristics of Equilibrium

  1. Occurs in a closed system

  2. Forward and backward reactions continue

  3. Rates become equal

  4. Concentrations stay constant

  5. Equilibrium can be reached from either direction

Dynamic Equilibrium

Equilibrium is called dynamic because reactions continue even though there is no visible change.

8.2 Equilibrium Constant

The equilibrium constant is represented by: Kc

It shows the relationship between products and reactants at equilibrium.

General Equation

For reaction:

aA+bB⇌cC+dD

Equilibrium constant:



Where:

  • means concentration

  • powers are coefficients

Example

N2​+3H2​⇌2NH3​


Equilibrium expression:


Meaning of (Kc)

Value of (Kc)Meaning
Large (Kc)Products favored
Small (Kc)Reactants favored

8.3 Factors Affecting Equilibrium

According to Le Chatelier’s Principle:

When a system at equilibrium is disturbed, it shifts to reduce the disturbance.

1. Effect of Concentration

  • Adding reactant → shifts right

  • Adding product → shifts left

Example:

N2​+3H2​⇌2NH3​

Adding hydrogen produces more ammonia.

2. Effect of Temperature

Exothermic Reaction

Heat is produced.

Increasing temperature:

  • equilibrium shifts backward

Endothermic Reaction

Heat is absorbed.

Increasing temperature:

  • equilibrium shifts forward

3. Effect of Pressure

Important for gases.

Increasing pressure:

  • equilibrium shifts toward fewer gas molecules

Example:

N2​+3H2​⇌2NH3​

Left side = 4 molecules
Right side = 2 molecules

Increasing pressure shifts reaction right.

4. Catalyst

A catalyst:

  • speeds up equilibrium

  • does NOT change equilibrium position

8.4 Industrial Application — Haber Process

Used to manufacture ammonia.

Reaction:

N2​+3H2​⇌2NH3​+heat

Conditions:

  • high pressure

  • moderate temperature

  • iron catalyst

Uses of Ammonia

  • fertilizers

  • nitric acid

  • explosives

Important Definitions

TermMeaning
Equilibrium    Forward and backward rates equal
Dynamic equilibrium    Reactions continue equally
(K_c)    Equilibrium constant
Catalyst    Speeds reaction without changing equilibrium

Short Tricks to Remember

TopicMemory Trick
Equilibrium        Equal rates
Large (K_c)        More products
High pressure        Fewer gas molecules
Catalyst        Faster only
Exothermic        Heat is product

Important Formula

Equilibrium Constant


General form:

Important Exam Questions

  1. What is chemical equilibrium?

  2. Define dynamic equilibrium.

  3. Write the expression for equilibrium constant.

  4. State Le Chatelier’s Principle.

  5. Explain effect of pressure on equilibrium.

  6. What is the role of catalyst in equilibrium?

  7. Explain Haber process.

Very Short Summary

  • Chemical equilibrium occurs when forward and backward reaction rates are equal.

  • (K_c) measures equilibrium position.

  • Concentration, temperature, and pressure affect equilibrium.

  • Catalysts only speed up reactions.

  • Haber process produces ammonia industrially.

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