3.1.4 Changes of State

• States of Matter

  • Solid
  • Liquid
  • Gas
• Solid

  Particles are tightly packed in a fixed structure and only vibrate in place
• Liquid

  Particles are close together but can move past one another, allowing the liquid to flow
• Gas

  Particles are far apart and move freely, filling the volume of their container
• Melting (Solid to Liquid)

  1. Solid is heated

  2. Particles gain energy

  3. Particles vibrate more vigorously

  4. Solid melts into liquid
• Freezing (Liquid to Solid)

  1. Liquid cools

  2. Particles lose energy

  3. Particles move more slowly

  4. Particles arrange into a fixed structure
• Boiling (Liquid to Gas)

  1. Liquid is heated

  2. Particles gain enough energy

  3. Particles break free from liquid state

  4. Become gas
• Evaporation (Liquid to Gas)

  1. Liquid at surface gains energy

  2. Particles become gas
• Condensation (Gas to Liquid)


  1. Gas cools

  2. Particles lose energy

  3. Particles move closer together

  4. Form a liquid
• Sublimation (Solid to Gas)

  1. Solid gains energy

  2. Particles break free from solid state

  3. Become gas
• Deposition (Gas to Solid)

  1. Gas changes directly into solid

  2. Without becoming a liquid
• Latent Heat

  The energy required for a substance to change state without changing temperature
• Latent Heat of Fusion


  Energy needed to melt a solid or freeze a liquid
• Latent Heat of Vaporization

  Energy needed to vaporize a liquid or condense a gas
• Heating and Cooling Curves

  • Heating Curve
  • Cooling Curve
• Heating Curve

  Shows how the temperature of a substance changes as it is heated over time
• Cooling Curve

  Shows how the temperature of a substance changes as it cools over time
• Flat Sections

  • Indicate changes of state, where temperature remains constant as energy is used to break intermolecular bonds (e.g., during melting or boiling)
  • Indicate changes of state, where temperature remains constant as energy is released when bonds form (e.g., during freezing or condensation)
• Increasing pressure can raise the boiling point of a liquid or lower the melting point of a solid
• The presence of impurities in a substance can alter its melting and boiling points
• Refrigerators use the principles of condensation and evaporation to remove heat from the interior and release it outside
• Radiators use the condensation of steam to release heat into a room
• Sublimation is used in freeze-drying, where water is removed from food or biological samples without passing through a liquid phase
• Understanding changes of state helps explain everyday phenomena, from water boiling to frost forming, and is essential for understanding broader concepts in thermodynamics and material science