State changes

• Changes of State

  There are six changes of state that can occur between solids, liquids and gases:

  Melting - When a solid turns into a liquid (e.g. ice to water)

  Evaporating - When a liquid turns into a gas

  Condensing - When a gas turns into a liquid

  Freezing - When a liquid turns into a solid

  Subliming - When a solid turns straight into a gas

  Desubliming - When a gas turns straight into a solid
• Conservation of Mass

  • When a substance changes state, the number of molecules in that substance doesn’t change and so neither does its mass
  • This is known as conservation of mass
  • During a change of state, the internal energy does change
  • Internal energy increases with an increase in temperature (from solid to gas)
• Physical vs Chemical Changes

  • Changes of state are physical changes
  • Physical changes are usually reversible
  • This means that the material recovers its original properties if the change is reversed
  • Physical changes are different to chemical changes because chemical changes are often not reversible
• 
  

  SOLID

  The molecules are very close together and arranged in a regular pattern

  The molecules vibrate about fixed position

  LIQUID

  The molecules are still close together (no gaps) but are no longer arranged in a regular pattern

  The molecules are able to slide past each other

  GAS

  The molecules are widely separated - about 10 times further apart in each direction

  The molecules move about randomly at high speeds
• STATE CHANGES:

  A) Solid

  B) Liquid

  C) Gases

  D) Melting

  E) Freezing

  F) Boiling

  G) Condensing

  H) Subliming