Changes of State and Particle Model

• Density


  The mass per unit volume of a material
• Density equation


  1. ⍴=m/v

  2. Density (kg/m³)

  3. Mass (kg)

  4. Volume (m³)
• States of matter in order of increasing density

  • Gas
  • Liquid
  • Solid
• Solid


  • Tightly packed in a regular arrangement
  • Particles can only vibrate on the spot
• Liquid


  • Close together, but with an irregular arrangement
  • They can flow over each other
• Gas


  • Separated, with no regular arrangement
  • Particles can move freely
• Mass is always conserved when a substance undergoes a change of state
• Change of state


  The material can return to having its previous properties if the change is reversed
• Chemical change


  The material cannot return to having its previous properties
• Sublimation


  A solid changes into a gas without passing through a liquid state
• Evaporation


  A liquid changes into a gas state
• Condensation


  A gas changes into a liquid state
• Water boils in an open pan

  The mass of the pan of water appears to decrease as some of the water evaporates and turns into water vapour, but the mass of the whole system remains constant
• Bathroom mirror mists up

  1. Hot water evaporates to form water vapour

  2. The water vapour lands on the cooler mirror

  3. The vapour condenses and returns to liquid state on the mirror's surface