Topic 14 ~ Particle Model

• Density


  Mass per unit volume
• Density depends on the spacing of the atoms in matter
• Solids and liquids


  • Have similar densities as the space between particles does not change significantly
  • Liquids usually have a lower density than solids (main exception is ice and water)
• Gases


  • Have a far lower density as the spacing between atoms increases x10, as the particles have lots of energy to move, so volume increases greatly and therefore the density decreases greatly compared to solids/liquids
• Mass is conserved during a change of state
• Physical changes are reversible, and not chemical changes
• Heating a system


  1. The amount of energy the particles have increases

  2. Particles vibrate more

  3. The temperature of the system increases

  4. OR the system changes state
• Changes of state


  • Melting
  • Evaporating
  • Freezing
  • Condensing
  • Sublimation
• Specific heat capacity


  The energy required to raise the temperature of 1kg of a substance by 1°C
• Specific latent heat


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

  Energy to melt/freeze
• Specific latent heat of vaporisation

  Energy to boil/condense
• Insulation


  • Reduces the amount of energy lost as it is a poor thermal conductor
  • Use reflective coatings to reflect IR radiation (heat) back into the system
• Pressure of a gas


  • Particles in a gas move randomly in every direction
  • A fluid can be a liquid or a gas
• Pressure produces a net force at right angles to any surface
• How pressure is exerted in a gas

  1. Particles collide with a wall, changing velocity

  2. This means they change momentum during their collision

  3. So they exert a force on the wall (as force = change in momentum/time)

  4. Pressure is the force across the area of the wall
• Increased temperature


  Increases pressure in a constant volume gas
• Absolute zero


  Temperature of 0 Kelvin or -273°C, the coldest possible temperature where particles have no energy and remain perfectly still
• Increasing the pressure of a gas


  Causes it to compress (have a smaller volume)
• Increasing the volume of a gas

  Causes the pressure to decrease
• Doing work on a gas

  Increases its temperature
• Adding more particles to a fixed volume

  Increases the pressure and temperature of the gas
• Decreasing the volume of a fixed number of gas particles

  Increases the pressure and temperature of the gas