(P3) PARTICLE MODEL OF MATTER

• 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
  • The spacing between atoms increase x10, as the particles have lots of energy to move, so volume increases greatly and therefore the density decreases greatly compared to solids/liquids
• If questions involve change in state and ask for new volume/pressure, the mass is the same
• Change of state

  • Mass is conserved
  • Physical changes are reversible, and not chemical changes
  • They are not chemical because the material retains its original properties when reversed
• Changes of state

  1. Melting

  2. Evaporating

  3. Freezing

  4. Condensing

  5. Sublimation
• Internal energy

  • Energy which is stored by particles (atoms and molecules) within a system
  • Takes the forms of kinetic energy (vibration of atoms etc.) and potential energy (between the particles)
• Heating a system


  • Increases the energy the particles have
  • This either raises the temperature of the system or produces a change of state
• Specific heat capacity


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


  • The amount of energy needed to change the state of 1kg of a substance without a change in temperature
  • Specific Latent Heat of fusion is energy to melt/freeze
  • Specific Latent Heat of vaporisation is energy to boil/condense
• Energy is absorbed when melting and evaporating and energy is released when freezing and condensing
• Sublimation is when solid goes straight to gas – "dry ice" (solid CO2 does this)
• Temperature changes of ice

  1. Solid

  2. Reaches 0°C

  3. Melting

  4. Liquid

  5. Boiling

  6. Gas
• Pressure


  The total force exerted by all of the molecules inside the container on a unit area of the walls
• Changing the temperature of a gas, held at constant volume


  Changes the pressure exerted by the gas (known as the Pressure law)
• Changing the volume of a gas


  • Affects the pressure
  • Increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure (known as Boyle's law)
• Doing work on a gas

  Increases its temperature
• Adding more particles to a fixed volume

  Increases the pressure and temperature of the gas
• A fixed number of particles in a smaller volume

  Increases the pressure and temperature of the gas
• 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 increase x10, as the particles have lots of energy to move, so volume increases greatly and therefore the density decreases greatly compared to solids/liquids
• If questions involve change in state and ask for new volume/pressure, the mass is the same!
• Changes of state


  • Mass is conserved during a change of state
  • Physical changes are reversible, and not chemical changes
  • They are not chemical because the material retains its original properties when reversed
• Changes of state


  • Melting
  • Evaporating
  • Freezing
  • Condensing
  • Sublimation
• Internal energy


  Energy which is stored by particles (atoms and molecules) within a system, in the forms of kinetic energy and potential energy
• Heating a system


  Increases the energy the particles have, which either raises the temperature of the system or produces a change of state
• Specific heat capacity


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


  The amount of energy needed to change the state of 1kg of a substance without a change in temperature
• Energy is absorbed when melting and evaporating and energy is released when freezing and condensing
• Sublimation is when solid goes straight to gas - "dry ice" (solid CO2 does this)
• Pressure in gases

  • The molecules of a gas are in constant random motion, and the temperature of the gas is related to the average kinetic energy of the molecules
  • The higher the temperature, the greater the average kinetic energy and so the faster the average speed of the molecules
  • When the molecules collide with the wall of their container they exert a force on the wall, and the total force exerted by all of the molecules inside the container on a unit area of the walls is the gas pressure
• Changing the temperature of a gas, held at constant volume


  Changes the pressure exerted by the gas (known as the Pressure law)
• Changing the volume of a gas

  • Affects the pressure
  • Increasing the volume in which a gas is contained, at constant temperature, can lead to a decrease in pressure (known as Boyle's law), this is due to the reduced number of collisions per unit area
• Increasing the pressure of a gas

  Doing work on a gas increases its temperature
• Adding more particles to a fixed volume

  • Doing work on a gas means compressing or expanding the gas, so changing the volume
  • Pumping more gas into the same volume means more particles are present, so more collisions occur per unit time with the walls, so pressure increases
  • Energy is transferred to the particles when more gas is added into the fixed volume, so this heats the gas
• A fixed number of particles for a smaller volume


  • The particles collide with the wall which is moving inward
  • The particles gain momentum, as the rebound velocity is greater than the approaching velocity
  • As the particle has a greater velocity, the pressure increases as the particles collide with the walls more frequently (time between collisions decreases)
  • The temperature also increases, as the kinetic energy of each particle increases