5. solid,liquid and gases

• Density


  Mass per unit volume, measured in kg/m³
• Finding the density of a liquid

  1. Measure mass of empty measuring cylinder

  2. Fill cylinder with liquid and measure new mass

  3. Subtract mass of empty cylinder to get mass of liquid

  4. Read volume from cylinder

  5. Calculate density using formula
• Finding the density of a solid

  1. Measure mass of solid

  2. If regularly shaped, measure dimensions and calculate volume

  3. If irregularly shaped, measure volume of water displaced

  4. Calculate density using formula
• Pressure


  Force per unit area, measured in Pascals (Pa)
• Pressure examples


  • Lying on bed of nails vs single nail
  • Pressure is lower on bed of nails as area is greater
• Pressure in fluids


  • Acts equally in all directions
  • Causes force at right angles to any surface
  • Created by movement of particles colliding with surface
• Pressure beneath liquid surface

  Increases with depth, density of liquid, and gravitational field strength
• Internal energy


  Increased by heating, can cause increase in temperature or change of state
• Heating a system


  1. Increases vibration of molecules and kinetic energy

  2. When changing state, energy used to separate molecules rather than increase kinetic energy
• Graph of temperature vs time when energy added

  • Ice rising in temperature
  • Ice melting into water
  • Water rising in temperature
  • Water boiling into steam
  • Steam rising in temperature
• Evaporation


  Escape of higher energy molecules from surface of liquid, cooling the liquid
• Factors affecting evaporation rate

  Increase temperature, increase surface area, provide a draught
• Solids


  • Molecules close together in regular pattern
  • Strong intermolecular forces of attraction
  • Molecules vibrate but can't move about
• Liquids


  • Molecules close together in random arrangement
  • Weaker intermolecular forces of attraction than solids
  • Molecules move around each other
• Gases


  • Molecules far apart in random arrangement
  • Negligible/very weak intermolecular forces
  • Molecules move quickly in all directions
• Specific heat capacity


  Amount of energy required to raise temperature of 1kg of substance by 1°C, measured in J/kg°C
• Gas molecules


  • Move rapidly and randomly due to collisions with other gas molecules
• Pressure exerted by gases

  Due to collisions between gas molecules and container walls, causing change in momentum and force
• Pressure and temperature of gas at constant volume

  As temperature increases, pressure increases
• Pressure and volume of gas at constant temperature

  As volume increases, pressure decreases
• Temperature in Kelvin


  Proportional to average kinetic energy of gas molecules