CIE IGCSE Physics: Kinetic Particle Model of Matter

States of Matter

• Three States of Matter: Solids, Liquids, Gases
  • Solids
  • Definite shape and volume
  • Cannot flow and are incompressible
  • Liquids
  • No definite shape, but definite volume
  • Able to flow and take the shape of a container; incompressible
  • Gases
  • No definite shape or volume
  • Highly compressible and can flow to fill a container

Changes of State

• When a substance changes state:

  • Mass remains unchanged
  • Energy changes
  • Physical changes are reversible

• Melting and Freezing:

  • Melting: Solid to liquid (e.g., ice to water)
  • Freezing: Liquid to solid

• Boiling and Condensing:

  • Boiling: Liquid to gas (also called evaporation)
  • Condensing: Gas to liquid

• Tip: Use water (ice, water, water vapor) as a reference for changes of state, but avoid mentioning it unless specified.

Molecular Matter

• Motion and Arrangement of Particles:

  • Solid:
  • Particles closely packed, regular arrangement
  • Vibrate in fixed positions
  • Liquid:
  • Still close, but no fixed arrangement, can slide past each other
  • Gas:
  • Particles far apart, random motion at high speeds

• Properties of States of Matter:

  • Density: High (Solid), Medium (Liquid), Low (Gas)
  • Particle Arrangement: Regular (Solid), Random (Liquid), Random (Gas)
  • Movement: Vibrate (Solid), Move past each other (Liquid), Move freely (Gas)
  • Energy: Low (Solid), Greater (Liquid), Highest (Gas)

Forces & Distances Between Particles

• The state of matter is influenced by intermolecular forces which:

  • Affect distances and motion of particles
  • Influence the ability to change shape, volume, and flow

• Solids:

  • Strong intermolecular forces keep molecules in fixed positions; rigid;

• Liquids:

  • Molecules can move around each other; same volume as solid; changes shape and flows.

• Gases:

  • High energy, random movement; easily compressed and expanded; flows freely.

Temperature & Pressure

• Temperature Effects:

  • As temperature increases, average speed of gas particles increases.
  • Higher temperatures imply greater kinetic energy.
  • Pressure is dependent on temperature, as energy and speed of particles increase with temperature.

• Pressure and Volume Relationship:

  • Pressure formula: p = \frac{F}{A} where:
  • p = Pressure in Pascals (Pa)
  • F = Force in Newtons (N)
  • A = Area in m²
  • Gases fill containers, causing pressure by particle collisions with container walls.

Brownian Motion

• Definition: Random motion of particles (e.g., pollen) suspended in a liquid or gas due to frequent collisions with smaller particles.

• Discovery: Described by Robert Brown; illustrated the constant motion of particles.

  • Observed through a microscope.

• Mechanism:

  • Small, fast-moving particles collide with larger visible particles (like pollen), causing them to move erratically.

Gas Laws

• Pressure & Volume (Constant Temperature)

  • Compression of gas decreases volume and increases pressure.
  • Expansion of gas increases volume and decreases pressure.

• Pressure & Temperature (Constant Volume)

  • Increasing temperature leads to increasing pressure, as particles collide with wall of container more often and forcefully.
  • Graphs indicate direct proportionality between pressure and temperature at constant volume.

• Key observations:

  • As the gas is compressed, molecular collision frequency increases, raising pressure.
  • At constant volume, higher temperatures yield higher pressure due to more frequent collisions with container walls.