States of matter

• Solids, Liquids and Gases

  Three states of matter that most substances exist in at room temperature
• Solids


  • Have a fixed volume and fixed shape
  • Cannot flow because particles cannot move from place to place
  • Cannot be compressed because particles are close together and have no space to move into
• Liquids


  • Have a fixed volume but no fixed shape
  • Can flow and take the shape of their container because particles can move around each other
  • Cannot be easily compressed because particles are close together and have no space to move into
• Gases


  • Have no fixed shape or volume
  • Can flow and completely fill their container because particles can move quickly in all directions
  • Can be compressed because particles are far apart and have space to move into
• Particle model


  Explains the difference between solids, liquids and gases
• All substances are made up of particles
• The particles are attracted to each other
• Some particles are attracted strongly to each other and others weakly
• The particles move around and have kinetic energy
• The kinetic energy of the particles increases with temperature
• Properties of solids, liquids and gases

  • Solids: Fixed volume and shape, cannot flow, cannot be compressed
  • Liquids: Fixed volume, no fixed shape, can flow, cannot be easily compressed
  • Gases: No fixed shape or volume, can flow, can be compressed
• Changes of state


  Reversible changes due to changes in pressure or temperature, unlike chemical reactions no new substance is formed
• Melting


  1. Solid changes into liquid

  2. Occurs at melting point

  3. Heat is absorbed during melting

  4. Impurities lower melting point and increase boiling point
• Pure substances melt and freeze at the same temperature, impure substances melt and boil through a range of temperatures
• During melting, heat energy is absorbed by the particles and converted to kinetic energy, causing the particles to vibrate faster and overcome attractive forces
• Temperature remains constant during melting as the absorbed heat energy is used to weaken attractive forces between particles, not increase kinetic energy
• Boiling


  1. Liquid changes into gas

  2. Occurs at boiling point

  3. Heat is absorbed during boiling

  4. Higher pressure results in higher boiling point

  5. Impurities affect boiling point
• During boiling, heat energy is absorbed by the particles, increasing their kinetic energy until they have enough energy to overcome attractive forces and escape the liquid to form a gas
• Temperature remains constant during boiling as the absorbed heat energy is used to weaken attractive forces between particles, not increase kinetic energy
• Evaporation


  Liquid changes into gas, occurs at surface of liquid, no fixed temperature, takes place below boiling point
• Condensation


  Gas changes to liquid when cooled to boiling point, heat is released to surroundings
• Freezing


  Liquid changes into solid, occurs at freezing point, impurities lower freezing point
• Sublimation


  Solid changes directly into gas, heat is absorbed, examples include dry ice, iodine, ammonium chloride
• The state of a substance at a given temperature can be predicted if its melting and boiling points are known
• Oxygen


  • Melting point -218°C, boiling point -183°C, so at -200°C oxygen will be in the liquid state
• Heating curve


  Graphical representation of changes of state during heating, shows melting and boiling
• Cooling curve


  Graphical representation of changes of state during cooling, shows condensation and freezing