particle theory

• density

  mass/volume
• gases

  • low density
  • particles have more energy in this state
  • increasing volume
  • decreasing density
• mass is always the same

  volume may change
• mass is conversed during

  state change
• sublimation

  solid to gas
• physical changes are reversible


  not chemical

  they are not chemical as material retains original properties when reversed
• heating system

  • amount of energy increases in particles
  • particles vibrate more
  • temperature increases or state changes
• specific heat capacity


  • amount of energy required to raise temperature of 1kg of a substance by 1$^o$c or kelvin
• specific heat capacity

  energy = mass x specific heat capacity x temp change
• specific latent heat

  • the energy to change 1kg of a substance without a change in temperature
• specific latent heat of fusion

  energy to melt/freeze something
• specific latent heat of vaporisation

  • energy to boil/condense
• energy is absorbed

  when melting or evaporating
• energy is released

  when freezing or condensing
• energy

  mass x specific latent heat

  E = ML
• insulation

  • thermal energy transfers out of a system
  • energy is wasted when lost to the surroundings
  • thermal insulators reduce energy lost
  • reflective coatings reflect IR radiation out of system
• pressure

  • force/area
• fluid

  liquid or gas
• pressure produces net force at right angles to any surface

  • particles collide with a wall change velocity
  • changes momentum during collision
  • force on wall = change of momentum/time
  • press is a force across the area of a wall
• temperature and pressure


  • increase temperature means more energy given to particles
  • thermal energy is transferred to kinetic collisions with walls occur more with greater impact
  • so pressure increases
• absolute zero

  • 0 kelvin or -273c
  • coldest temperature
  • particles at this temperature have no energy
  • they remain still
• Celsius to kelvin

  c - 273 = K
• gas and change

  • pressure causes gas to compress or expand
  • same force is exerted on walls as temperature and energy is constant
  • pressure is inversely proportional to volume
  • p = 1/vol
  • p1v1 = p2v2
• work done on gas

  • pressure x volume
  • or force x distance
  • force/area x (area x distance)
• adding particles to a fixed volume

  • more collisions
  • energy is transferred to particles when gas is added so it heats up
• fixed number of particles to a decreasing volume

  • particles collide with the wall which is moving inward
  • momentum is gained as rebound velocity is greater then approaching velocity
  • this greater velocity increases pressure as particles collide with the walls more
  • temperature increases as kinetic energy increases