P3

• Particle model of matter


  Everything is made up of lots of tiny particles
• Particle theory


  • You can think of the particles that make up matter as tiny balls
  • You can explain the ways that matter behaves in terms of how these tiny balls move, and the forces between them
• States of matter


  • Solid (e.g. ice)
  • Liquid (e.g. water)
  • Gas (e.g. water vapour)
• Solids


  • Strong forces of attraction hold the particles close together in a fixed, regular arrangement
  • Particles don't have much energy so they can only vibrate about their fixed positions
• Liquids


  • Weaker forces of attraction between the particles
  • Particles are close together, but can move past each other, and form irregular arrangements
  • Particles have more energy than in a solid - they move in random directions at low speeds
• Gases


  • Almost no forces of attraction between the particles
  • Particles have more energy than in liquids and solids - they're free to move, and are constantly moving with random directions and speeds
• Colliding gas particles create pressure


  1. Particles in gases are free to move around

  2. As they move, they bang into each other and whatever else happens to get in the way (like the sides of the container they're being kept in)

  3. When they collide with something, they exert a force on it

  4. Pressure is the force exerted per unit area

  5. In a sealed container, the outward gas pressure is the total force exerted by all of the particles in the gas on a unit area of the container walls
• Increasing the temperature of a gas

  Can increase its pressure
• Internal energy


  The total energy stored by particles in a system
• Internal energy


  • Particles in a system have energy in their kinetic energy stores
  • Particles in a system have energy in their potential energy stores due to their positions
  • Heating the system transfers energy to its particles, increasing the internal energy
  • This leads to a change in temperature or a change in state
• A change of state conserves mass
• Changes of state


  • Sublimating
  • Freezing
  • Melting
  • Boiling or evaporating
  • Condensing
• A change of state is a physical change, not a chemical change
• Specific latent heat


  The energy needed to change the state of a 1 kg mass
• Specific latent heat of fusion


  The specific latent heat for changing between a solid and a liquid (melting or freezing)
• Specific latent heat of vaporisation

  The specific latent heat for changing between a liquid and a gas (evaporating, boiling or condensing)
• Calculating specific latent heat

  Energy (E) = Mass (m) x Specific Latent Heat (L)
• solids


  • In solids, strong attractive forces hold the particles in place, so that they can only vibrate in position.
  • As the substance is heated the particles gain energy and vibrate faster and faster. Eventually, the particles have so much energy that they can overcome the forces holding them together and the substance melts into a liquid
• Gas


  • When a gas is heated, the particles gain kinetic energy and move faster. 
  • If the gas is trapped within a container that cannot expand, it means that the volume of the gas is fixed, and so the pressure inside the container increases