Table of Contents

• 1: KINETIC THEORY OF MATTER
  • 1.1 Overview of the Kinetic Theory of Matter
  • 1.2 Key Assumptions of the Kinetic Theory of Matter
• 2: CHANGES OF STATE IN TERMS OF MOLECULAR MOTION
  • 2.1 Introduction
  • 2.1 Melting (Solid to Liquid)
    • Definition:
    • Molecular Explanation:
    • Example:
    • Factors Affecting Melting:
  • 2.2 Vaporization (Liquid to Gas)
    • Definition:
    • Molecular Explanation:
    • Types of Vaporization:
      • (a) Evaporation
      • (b) Boiling
    • Factors Affecting Vaporization:
  • 2.3 Freezing (Liquid to Solid)
    • Definition:
    • Molecular Explanation:
    • Example:
    • Factors Affecting Freezing:
  • 2.4 Condensation (Gas to Liquid)
    • Definition:
    • Molecular Explanation:
    • Example:
    • Factors Affecting Condensation:
  • 2.5 Brownian Motion
    • Definition:
    • Molecular Explanation:
    • Example:
    • Significance of Brownian Motion:
  • 2.6 Summary of Changes of State
  • 2.7 Key Takeaways

1: KINETIC THEORY OF MATTER

1.1 Overview of the Kinetic Theory of Matter

The kinetic theory of matter states that all substances (solids, liquids, and gases) are made up of tiny particles (atoms, molecules, or ions) that are in constant motion. The behavior of these particles explains the properties of different states of matter and the changes that occur between them.

1.2 Key Assumptions of the Kinetic Theory of Matter

1. All matter is composed of small particles (atoms, molecules, or ions).
2. The particles are in constant motion and possess kinetic energy.
3. The degree of motion depends on temperature; increasing temperature increases particle motion.
4. There are forces of attraction between particles; these forces are strongest in solids, moderate in liquids, and weakest in gases.
5. Collisions between particles are elastic, meaning there is no net loss of energy during collisions.

2: CHANGES OF STATE IN TERMS OF MOLECULAR MOTION

2.1 Introduction

Changes of state refer to the transformation of matter from one physical state to another due to the absorption or release of heat energy. These changes occur because heat energy affects the kinetic energy of the particles, altering their movement and the strength of the intermolecular forces between them.

The kinetic theory of matter states that all substances are made up of particles in constant motion. The amount of kinetic energy these particles possess determines the physical state of the substance. When energy is added (heating) or removed (cooling), the movement of particles changes, leading to a change in state.

The major changes of state include:

1. Melting (Solid to Liquid)
2. Vaporization (Liquid to Gas)
3. Freezing (Liquid to Solid)
4. Condensation (Gas to Liquid)
5. Brownian Motion (Random particle movement in fluids)

Each of these processes is explained in detail below.

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2.1 Melting (Solid to Liquid)

Definition:

Melting is the process where a solid changes into a liquid due to an increase in temperature.

Molecular Explanation:

• In a solid, particles are tightly packed in a fixed structure and can only vibrate in place.
• When heat is applied, the particles absorb kinetic energy and vibrate more rapidly.
• At a certain temperature known as the melting point, the particles gain enough energy to overcome the strong intermolecular forces holding them together.
• The solid structure breaks down, and the substance transforms into a liquid, where the particles can move past each other more freely.

Example:

• Ice melts into water at 0°C (273 K).
• The melting of butter when heated.

Factors Affecting Melting:

1. Type of Substance – Different materials have different melting points based on their intermolecular forces.
2. Pressure – Increasing pressure can alter the melting point of certain substances.
3. Purity of Substance – Impurities lower the melting point (e.g., salt added to ice causes it to melt at a lower temperature).

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2.2 Vaporization (Liquid to Gas)

Definition:

Vaporization is the process where a liquid changes into a gas when heated.

Vaporization occurs in two forms:

1. Evaporation – A slow process that occurs at all temperatures.
2. Boiling – A rapid process that occurs at a fixed boiling point.

Molecular Explanation:

• In a liquid, particles move more freely than in a solid but are still held together by intermolecular forces.
• When heat is applied, the particles absorb energy, move faster, and eventually gain enough kinetic energy to break free from the liquid’s surface into the gas phase.

Types of Vaporization:

(a) Evaporation

• Occurs at any temperature below the boiling point.
• Happens at the surface of the liquid where molecules with enough energy escape into the gas phase.
• Example: Water drying on clothes after washing, even without boiling.

(b) Boiling

• Occurs when the liquid reaches its boiling point, where all particles have enough energy to become gas.
• Example: Water boils at 100°C (373 K) at standard atmospheric pressure.

Factors Affecting Vaporization:

1. Temperature – Higher temperatures increase the rate of vaporization.
2. Surface Area – A larger surface area allows more particles to escape.
3. Wind and Air Movement – Moving air (like wind) removes vaporized molecules, increasing evaporation.
4. Humidity – High humidity reduces evaporation since the air is already saturated with water vapor.

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2.3 Freezing (Liquid to Solid)

Definition:

Freezing is the process where a liquid changes into a solid due to a decrease in temperature.

Molecular Explanation:

• In a liquid, particles move freely but are still loosely connected by intermolecular forces.
• When the temperature decreases, the particles lose kinetic energy and move more slowly.
• At the freezing point, particles settle into a fixed, orderly structure, forming a solid.

Example:

• Water freezes into ice at 0°C (273 K).
• Formation of ice cubes in a freezer.

Factors Affecting Freezing:

1. Purity of the Liquid – Impurities lower the freezing point (e.g., adding salt to water prevents freezing at 0°C).
2. Pressure – Higher pressure can affect the freezing point of certain substances.

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2.4 Condensation (Gas to Liquid)

Definition:

Condensation is the process where a gas changes into a liquid when cooled.

Molecular Explanation:

• In a gas, particles move very quickly and are far apart.
• When the gas cools, the particles lose kinetic energy and move closer together.
• At the dew point, the particles condense to form a liquid.

Example:

• Water vapor condenses on a cold glass surface.
• Formation of dew on grass in the morning.

Factors Affecting Condensation:

1. Temperature – Lower temperatures increase condensation.
2. Pressure – Higher pressure forces gas particles closer together, promoting condensation.

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2.5 Brownian Motion

Definition:

Brownian motion is the random movement of microscopic particles suspended in a fluid (liquid or gas) due to collisions with the molecules of the medium.

Molecular Explanation:

• Small particles (such as pollen grains) suspended in a liquid or gas move in a random, zigzag pattern.
• This motion occurs because the particles are constantly bombarded by the moving molecules of the surrounding fluid.
• The movement is more noticeable in smaller particles and in gases where molecular motion is faster.

Example:

• Pollen grains moving randomly in water under a microscope.
• Smoke particles moving erratically in air.

Significance of Brownian Motion:

1. Evidence for the Kinetic Theory of Matter – Confirms that molecules are constantly moving.
2. Explains Diffusion – The movement of particles leads to the mixing of substances.

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2.6 Summary of Changes of State

Change of State	Process	Energy Transfer	Example
Melting	Solid → Liquid	Heat absorbed	Ice melting into water
Vaporization	Liquid → Gas	Heat absorbed	Water boiling at 100°C
Freezing	Liquid → Solid	Heat released	Water freezing into ice
Condensation	Gas → Liquid	Heat released	Water vapor forming dew
Sublimation	Solid → Gas	Heat absorbed	Dry ice (solid CO₂) turning to gas

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2.7 Key Takeaways

• Changes of state occur due to heat energy affecting the kinetic energy of particles.
• Melting happens when a solid absorbs heat, causing it to turn into a liquid.
• Vaporization occurs when a liquid gains energy and changes into gas (evaporation or boiling).
• Freezing happens when a liquid loses energy and turns into a solid.
• Condensation is when gas cools and transforms into a liquid.
• Brownian motion provides evidence for the constant motion of particles.

Chapter 3: Gas Laws

Gas laws describe the relationships between pressure, volume, temperature, and the number of molecules in a gas. They help in understanding how gases behave under different conditions.

• Boyle’s Law (Pressure-Volume Relationship)
• Charles’ Law (Temperature-Volume Relationship)
• Graham’s Law of Diffusion (Rate of Gas Diffusion)
• Dalton’s Law of Partial Pressures (Pressure in Gas Mixtures)
• The Combined Gas Law (Relationship Between Pressure, Volume, and Temperature)

3.1 Boyle’s Law (Pressure-Volume Relationship)

Statement: At constant temperature, the volume (V) of a given mass of gas is inversely proportional to its pressure (P).

P ∝ 1/V or P × V = k

Mathematical Expression:

P₁V₁ = P₂V₂

Example 1: Solved Calculation

Example 2: Solved Calculation

3.2 Charles’ Law (Temperature-Volume Relationship)

Statement: At constant pressure, the volume (V) of a gas is directly proportional to its absolute temperature (T) in Kelvin.

V ∝ T or V₁/T₁ = V₂/T₂

Example 1: Solved Calculation

3.3 Graham’s Law of Diffusion

Statement: The rate of diffusion of a gas is inversely proportional to the square root of its molar mass.

r₁/r₂ = √(M₂/M₁)

Example 1: Solved Calculation

Example 2: Solved Calculation

Summary

This guide provides a detailed explanation of Boyle’s Law, Charles’ Law, and Graham’s Law using real-world examples and calculations.

4: The Ideal Gas Equation

The **Ideal Gas Equation** is a fundamental equation in chemistry that describes the behavior of an ideal gas. It is given by:

PV = nRT

Where:

• P = Pressure (atm or Pa)
• V = Volume (L or m³)
• n = Number of moles of gas
• R = Gas constant (0.0821 L·atm/mol·K or 8.314 J/mol·K)
• T = Temperature (Kelvin)

Example Calculation

5: Relationship Between Vapour Density and Relative Molecular Mass

The **vapour density (VD)** of a gas is related to its **relative molecular mass (M)** by the equation:

M = 2 × VD

Example Calculation