3.2.3 Changes of State & Specific Latent Heat

• What happens to the temperature of a substance whilst it changes state?

  The temperature remains constant during a change of state.
• What is boiling?

  When a substance changes state from a liquid to a gas.
• The graph shows a substance cooling over time, changing state from a gas to a liquid, then from a liquid to a solid. What is the name of the two temperatures A and B on the graph?

  A = boiling point

  B = melting point

  
• What is specific latent heat?

  The energy required to change 1kg of a particular substance from one state to another, without a change in temperature.
• What does the specific latent heat of fusion refer to?

  The amount of heat required to change a substance from a solid to a liquid (or vice versa).
• What does the specific latent heat of vaporisation refer to?

  The amount of heat required to change a substance from a liquid to a gas (or vice versa).
• What is the formula for specific latent heat?

  Specific latent heat = energy / mass.
• 2 kg of ice melts and becomes water. How much energy did it take to melt the ice? (The latent heat of fusion of ice is 334,000 J/kg)

  668,000J.
• 0.4 kg of water at 100°C boils to become steam. How much energy did it take to boil the water? (The latent heat of vaporisation of water is 2,260,000 J/kg)

  904,000J.
• What is the formula for energy for a change of state?

  Energy for a change of state = mass x specific latent heat.
• What is energy measured in?

  Joules.
• What is mass measured in?

  Kilograms.
• What is specific latent heat measured in?

  Joules per kilogram (J/kg).
• What are the flat parts of the graph?

  Where energy is being transferred by heating but not being used to change the temperature.
• What is happening in the boiling graph?

  Internal energy is increasing and bonds are breaking.
• What is happening in the cooling graph?

  Internal energy is decreasing and bonds are forming.