Changes of matter

• Sublimation


  A substance can change directly from solid to gas without becoming a liquid in between
• Substances that can sublime


  • Solid carbon dioxide ('dry ice')
• Melting, evaporating and boiling how.

  1. Energy must be transferred, by heating, to a substance for these changes of state to happen

  2. During these changes the particles gain energy, which is used to:

  3. Break some of the bonds between particles during melting

  4. Overcome the remaining forces of attraction between particles during evaporating or boiling
• Evaporation


  Particles leave a liquid from its surface only
• Boiling


  Bubbles of gas form throughout the liquid, they rise to the surface and escape to the surroundings, forming a gas
• Melting point


  The temperature at which a solid changes to a liquid
• Boiling point


  The temperature at which a liquid changes to a gas
• 
  

  The stronger the forces, the more energy is required to change state
• Factors affecting melting and boiling points

  • Type of bonding
  • Particles involved
• Evaporation can take place below the boiling point of a substance
• Condensing and freezing what happens.


  1. Energy is transferred from a substance to the surroundings when a substance condenses or freezes

  2. This is because the forces of attraction between the particles get stronger
• Predicting the state of a substance

  • Given temperature < melting point: Solid
  • Given temperature is between melting and boiling points: Liquid
  • Given temperature > boiling point: Gas
• The particle model assumes that particles are solid spheres with no forces between them, but this is a limitation as particles are not solid, since atoms are mostly empty space
• Deposition: changing directly from a gas to a solid (without becoming a liquid)