Kinetic theory

• Diffusion


  Particles spread out from where they are in high concentrations to where they are in low concentrations
• Diffusion is evidence that something spreads out – this something is a particle
• Coloured compounds can be diluted many times before the colour disappears, which is evidence that particles must be very small
• States of matter


  • Solids
  • Liquids
  • Gases

  
• A substance can usually exist in all three states, dependent on temperature (and pressure)
• Melting


  Solid → Liquid (when heating up)
• Freezing


  Liquid → Solid (when cooling down)
• Boiling


  Liquid → Gas (when heating up)
• Condensing


  Gas → Liquid (when cooling down)
• Solid


  • Close arrangement, Ordered, Vibrate around fixed positions
• Liquid


  • Close arrangement, Random, Move freely past each other
• Gas


  • Far apart arrangement, Random, Move completely freely
• Melting of a solid

  Particles gain kinetic energy, moving faster, until they have enough energy to overcome the forces holding them together and start to move past each other forming a liquid
• Boiling of a gas

  Particles lose kinetic energy, moving more slowly, forces of attraction start to form between the particles, the forces start to hold the particles together as a liquid
• Ammonium Chloride Tube


  • Two gases, ammonia and hydrogen chloride, diffuse from the ends of the sealed tube, where they meet the compound ammonium chloride forms as a white smoke
• The hydrogen chloride molecules must be heavier, as they diffused slower
• If you heat up the tube

  The white smoke forms faster because the particles move faster and collide more often