Particle Model And 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 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


  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 (Pressure law)
• Pressure in gases


  • 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 (Boyle's law)
  • Increasing the pressure of a gas does work on the gas, which increases its temperature
• Adding more particles to a fixed volume increases the pressure, as there are more collisions per unit time with the walls, and this also heats the gas
• A fixed number of particles in a smaller volume increases the pressure, as the particles collide with the walls more frequently and gain more momentum, which also increases the temperature
• In solids, the particles vibrate around fixed positions but do not move far from their position.
• Solids have a definite shape and volume.
• The particles are held together by strong forces.