P6 Molecules & Matter

• Density


  Mass per unit volume
• Density = mass / volume
• 1 litre = 1000 ml
• Measuring the volume of an irregular solid object

  1. Smaller solid: Measure the change in level of the water in a measuring cylinder

  2. Larger solid: Fill a eureka can with water until it stops dripping from the spout, then lower the object and measure the volume of water displaced in the measuring cylinder
• Internal Energy


  The total energy the particles have
• Internal Energy


  1. Kinetic energy

  2. Potential energy
• What happens to the kinetic energy when the temperature rises? 


  The particles will vibrate / move faster. This increases their kinetic energy
• What happens to the potential energy when temperature rises?

  The particles will start to move away from one another. Increases potential energy.
• Specific Heat Capacity


  The energy needed to raise the temperature of 1kg of the substance by 1°C without a change of state
• Specific Latent Heat


  The amount of energy that is needed to change the state of 1kg of substance at constant temperature
• Specific latent heat 'I'

  The amount of energy that is needed to change the state of 1kg of substance at constant temperature
• Specific latent heat calculation

  1. Energy transferred (J)

  2. Mass (kg)
• When a substance changes from solid to liquid or from liquid to gas, it takes energy to change its state
• Heat energy is needed to break bonds or separate the molecules
• The temperature remains the same when a substance changes state
• Specific Latent heat of a substance

  The amount of energy needed to change the state of 1 kg of substance at constant temperature
• Latent heat of fusion


  The latent heat involved when a substance changes from solid to liquid
• Latent heat of vaporisation


  The latent heat involved when a substance changes from liquid to vapour
• Temperature is a measure of the average kinetic energy of the particles in a substance
• Boiling point is the temperature at which a liquid changes to a gas
• Melting point is the temperature at which a solid changes to a liquid
• Increasing the temperature increases the speed of the molecules so they will collide more often, and with a bigger force with the walls of the container, exerting a bigger pressure
• Kinetic theory

  Everything is made of molecules (or particles) in constant random motion (brownian motion)
• How gas pressure is exerted

  1. Molecules collide with the walls of the container

  2. Exert a force on the walls

  3. This is pressure
• When temperature increases

  Pressure increases
• What happens when temperature increases

  • Particles gain more kinetic energy
  • They will collide more often
  • They will collide with a bigger force with the walls of the container
• Investigating gas pressure and temperature


  1. Dry air sealed in a flask

  2. Flask placed in water bath

  3. Water bath heated to raise gas temperature

  4. Water stirred to ensure even temperature

  5. Temperature measured with thermometer

  6. Pressure read from pressure gauge
• As temperature increases


  Pressure increases