Changing state

• Solid


  State of matter where particles are held tightly in fixed positions
• Liquid


  State of matter where particles can move around but are still close together
• Gas


  State of matter where particles can move around freely with a lot of space between them
• Melting


  When a solid is heated, its particles gain energy and start to move about, breaking some of the forces between the particles, until at the melting point the particles have enough energy to break free from their positions and the solid turns into a liquid
• Boiling


  When a liquid is heated, the particles get even more energy, the forces holding the liquid together weaken and break, until at the boiling point the particles have enough energy to break the forces and the liquid becomes a gas
• Freezing


  When a liquid cools, the particles have less energy and move around less, the forces between the particles become stronger, until at the melting point the forces between the particles are so strong that they're held in place and the liquid becomes a solid
• Condensing


  At the boiling point, the forces between the particles in the gas become strong enough that the gas becomes a liquid
• The amount of energy needed for a substance to change state depends on how strong the forces between particles are
• The stronger the forces, the more energy is needed to break them, and so the higher the melting and boiling points of the substance
• Predicting the state of a substance


  1. If the temperature is below the melting point, the substance will be a solid

  2. If the temperature is above the boiling point, the substance will be a gas

  3. If the temperature is between the melting and boiling points, the substance will be a liquid