particle model of matter

• Density

  Mass for a given volume
• Density equation

  Density = Mass / Volume
• solids usually have a high density because the particles are packed closely together so solids have a lot of mass for their volume
• Liquids usually have a high density because the particles are close together do they have a lot of mass for their volume.
• Gasses have a low density because the particles are very far apart so gases only have a small mass for their volume.
• Polystyrene is a solid but it has a low density because it has a a very open structure and is full of air spaces so it has a small mass for its volume.
• particles gave potential energy

  • intermolecular forces
  • chemical bonds
• internal energy is all the energy stored in a system by the particle including the kinetic energy of the particles and the potential energy of the particles
• • if we heat a solid
  • we increase the internal energy
  • at some point the solid can turn into a liquid
• • if we cool a gas
  • we reduce internal energy
  • so at some point the gas turns back into liquids
• sublimation - when a solid directly turns into a gas
• when changes of state take place mass is always conserved.
• changes of state are physical changes not chemical changes
• evaporation is when a liquid turns into a gas but only the surface of a liquid because only the particles in the surface have enough energy to turn them into a gas
• latent heat is the energy required for a substance to change state
• during the change of a state we are increasing the internal energy store but we are not changing the temperature
• when the substance changes state the temperature stops increasing and stays constant because now the energy that we are putting is weakening/breaking the forces of attraction between particles
• specific latent heat - the amount of energy required to change the state of one kg of the substance with no change in temeprature
• energy for a change of state (J) = mass (Kg) x specific latent heat (J/Kg)
• the pressure of a gas is due to the particles colliding with the walls of the container that the gas is held in.
• at high temperatures, particles have higher kinetic energy so there are more successful collisions per second with more force so there is higher pressure.