Particle model of matter

• Density is the measure of the 'compactness' of a substance.
• A dense material has its particles closely packed together. A less dense material has its particles more spread out.
• Solids:

  • Strong forces hold the particles in fixed, regular arrangements.
  • The particles can only vibrate in position
  • Generally the most dense
• Liquids:

  • The particles are close but can move past each other
  • More energy in the particles than a solid
  • Move in random directions at low speeds
• Gases:

  • Almost no forces of attractions between particles
  • Free to move in random directions at high speeds
  • Generally the least dense
• Density = mass / volume
• The internal energy of a system is the sum of the kinetic and potential energy stores.
• A change in state occurs if the object is heated enough: the object has enough energy in their kinetic stores to break the bonds holding them together.
• A change of state is a physical change - you don't end up with a new substance like a chemical reaction.
• Mass is conserved when an object changes state.
• The energy needed to change the state of 1kg of a substance is called specific latent heat.
• When a substance is changing state, there will be flat parts on the time/temperature graph. This is because the energy being supplied is used for breaking the bonds between particles rather than heating the substance.
• For cooling, specific latent heat is the amount of energy released by a change in state.
• Specific latent heat is different for different materials, and for changing between different states.
• The specific latent heat for melting or freezing is called specific latent heat of fusion.

  The specific latent heat for evaporating, boiling or condensing is called the specific latent heat of vapourisation.
• The particles in a gas are constantly moving with random direction and speeds.
• If you increase the temperature of a gas, you transfer energy into the kinetic energy stores of its particles.
• When gas particles collide with something, they exert a force. This is called pressure.
• Increasing the temperature of a gas, or decreasing the volume of the container, increases the pressure.
• Pressure and volume are inversely proportional.
• The pressure of a gas causes a net outwards force at right angles to the surface of the container.
• Doing work on a gas increases its temperature.