particle model of matter

• Solids:

  • strong forces of attraction hold particles close together in a fixed, regular arrangement
  • particles don't have much energy so only vibrate about their fixed positions
  • density is the highest as particles are closest together

  
• Liquids:

  • weaker forces of attraction between particles
  • particles are close but can move past each other and form irregular arrangements
  • particles will have more energy than solids, so move in random directions at low speed
  • less dense than solids

  
• Gases:

  • almost no force of attraction between particles
  • they have more energy so are free to move, and travel in random directions at high speeds
  • low density

  
• D = mass/volume
• Internal Energy


  The total energy that the particles in a system have in their kinetic and potential energy stores
• How Heating Affects Internal Energy

  1. Heating the system transfers energy to its particles (they gain energy in their kinetic stores and move faster), increasing the internal energy

  2. This leads to a change in temperature or a change in state

  3. The size of the temperature change depends on the mass of the substance, what it's made of (its specific heat capacity) and the energy input
• Change of State


  A physical change where the particles have enough energy in their kinetic energy stores to break the bonds holding them together
• A change of state is a physical change, not a chemical change
• Mass is conserved during a change of state
• Specific Latent Heat (SLH)

  The amount of energy needed to change 1 kg of a substance from one state to another without changing its temperature
• Specific Latent Heat of Fusion


  The specific latent heat for changing between a solid and a liquid
• Specific Latent Heat of Vaporisation


  The specific latent heat for changing between a liquid and a gas
• Temperature doesn't change during a change of state
• Average Energy in Kinetic Stores

  Related to the temperature of a gas - the higher the temperature, the higher the average energy
• Increasing the temperature of a gas

  Increases the average speed of its particles
• Gas Pressure


  The total force exerted by all of the particles in the gas on a unit area of the container walls
• Increasing the speed of gas particles

  Increases the gas pressure
• Increasing the volume of a gas at constant temperature


  Decreases the gas pressure
• Decreasing the pressure outside a container


  Causes the container to expand
• How Doing Work on a Gas Increases its Temperature

  1. Doing work on a gas increases its internal energy, which can increase its temperature

  2. You can do work on a gas mechanically, e.g. with a bike pump

  3. This transfers energy to the kinetic energy stores of the gas particles, increasing the temperature