Heating and changes of state

• 2 changes to the particles when a material is heated or cooled

  1. Chemical bonds between the particles may form, break or stretch. There is a change in the chemical potential store of energy in the material
  2. The material will heat up or cool down as the particles within it may gain or lose speed. There is a change in the thermal store of energy within the material
• The internal energy is the total amount of energy in the thermal and chemical potential stores of all the particles in the system
• When energy is given to raise the temperature, particles speed up and gain energy
• Conservation of energy


  The principle that the total energy of a system stays the same, that energy cannot be created or destroyed (only stored or transferred)
• • when a substance melts or boils, energy is put in to breaking the bonds that are holding particles together, which increases the energy in the system.
  • throughout all of these changes the total number of particles, or mass, does not change.
• • the bonds between particles in one substance may have a different strength to the bonds between particles in another substance.
  • if these bonds are stronger, more internal energy will be needed to break them and so the temperature for melting or boiling will be higher.