topic 14 particle model

• density = mass / volume
• Particles in solids

  • particles are arranged in rows
  • particles vibrate around a fixed point
  • there are forces of attraction between the particles but they do not have enough energy to overcome these forces
• Particles in liquid


  • particles are randomly arranged
  • particles can move around
  • particles have more energy than solids so can overcome these attractions
  • no fixed shape
• Particles in gases


  • particles arranged randomly and far apart
  • lots of energy to overcome these attractions
  • particles are moving quickly in all directions
• Density between states of matter

  Most dense in solids, least dense in gas form

  In solids, the particles are more closer together

  In gases, the particles are more far apart
• Mass is conserved


  When substances change state, mass is conserved
• When substance changes state, volume changes
• Physical changes differ from some chemical changes because the material recovers its original properties if the change is reversed
• Heating a substance

  • increases the energy in its thermal energy store or kinetic energy store
• Internal energy


  sum of the energy in the kinetic and potential stores of the particles
• The more energy stored means the speed of the vibrating particles increases
• If enough energy is stored, the particles vibrate fast enough in order to break the molecular forces between the particles, causing it to change state
• Temperature


  the movement of particles
• Specific heat capacity


  the amount of energy needed to increase the temperature by 1 degrees Celsius of 1 kg of that substance
• Specific latent heat


  The amount of energy needed to change the state of 1 kg of a substance
• Differences between SHC and SLH

  • SHC measures the change in temperature whereas SLH is the change in state
  • SHC causes the temperature change whereas in SLH there is no temperature
  • SLH is the amount of energy in joules whereas SHC is the quantity of heat measured in degrees Celsius
• change in thermal energy = mass x SHC x change in temperature
• thermal energy for a change of state = mass x SLH
• Reducing unwanted energy transfer through thermal insulation

  insulating materials:

  • wool, foam, bubble wrap
• What does insulation prevent?

  it prevents any more thermal energy from being transferred to the surroundings