IGCSE Chemistry: Chapter 1 – States of Matter

1. Introduction: The Three States of Matter

Matter exists in three primary states: solids, liquids, and gases. Each state has distinct properties determined by the forces between their particles:

• Solids: Fixed volume and shape.
• Liquids: Fixed volume but conform to the shape of their container.
• Gases: No fixed volume or shape, expanding to fill their container.

2. Kinetic Particle Theory

The kinetic particle theory explains the behavior of matter in different states:

• All matter consists of tiny particles in constant motion.
• The energy and arrangement of particles determine the state of matter.

3. Particle Behavior in Different States

• Solids: Particles are tightly packed and vibrate around fixed positions, giving solids a definite shape.
• Liquids: Particles are close together but can move around, allowing them to flow and take the shape of their container.
• Gases: Particles are widely spaced and move freely with high energy, filling their container with no fixed shape or volume.

4. State Changes and Energy

State changes occur when a substance absorbs or releases thermal energy:

• Heating: Provides energy to particles, leading to transitions such as:
  • Melting: Solid → Liquid
  • Boiling/Evaporating: Liquid → Gas
• Cooling: Removes energy, causing transitions such as:
  • Condensing: Gas → Liquid
  • Freezing: Liquid → Solid

5. Evaporation

Evaporation is when faster-moving liquid particles escape from the surface to form gas particles. The rate of evaporation increases with temperature as more particles gain energy to escape.

6. Diffusion

Diffusion is the random movement and mixing of particles in liquids and gases. The rate of diffusion depends on factors such as:

• Temperature: Higher temperatures increase particle movement.
• Particle mass: Lighter particles diffuse faster than heavier ones.

7. Beyond the Three States

Some substances exhibit properties of multiple states, challenging traditional classifications:

• Liquid crystals: Flow like liquids but have ordered particle arrangements.
• Superfluids: Liquids with zero viscosity at extremely low temperatures.
• Plasma: Ionized gases with unique properties such as electrical conductivity, often referred to as the fourth state of matter.

8. Pressure and Temperature Effects on Gases

• Temperature: Increasing temperature increases gas volume as particles gain energy and occupy more space.
• Pressure: Increasing pressure decreases gas volume by compressing particles closer together.

9. Heating and Cooling Curves

Heating and cooling curves show how temperature changes with heat energy during state transitions:

• Heating curves: Represent temperature increases as substances absorb heat.
• Cooling curves: Represent temperature decreases as substances release heat.