Specific latent heat+particle motion

• If you heat up a pan of water on the stove, the water never gets any hotter. You can keep beating it up, but the temperature won't rise.
• Latent heat


  The energy needed to change the state of a substance
• When a substance is melting or boiling

  1. Energy is being transferred by heating but not being used to change the temperature

  2. Energy is used for breaking bonds between particles rather than raising the temperature
• When a substance is condensing or freezing

  1. Bonds are forming between particles, which releases energy

  2. The temperature doesn't go down until all the substance has turned to liquid (condensing) or a solid (freezing)
• Specific latent heat


  The amount of energy needed to change 1 kg of a substance from one state to another without changing its temperature
• Specific latent heat is different for different materials, and for changing between different states
• Specific latent heat of fusion

  The specific latent heat for changing between a solid and a liquid (melting or freezing)
• Specific latent heat of vaporisation


  The specific latent heat for changing between a liquid and a gas (evaporating, boiling or condensing)
• Specific latent heat is about changes of state with no temperature change, unlike specific heat capacity which relates to a temperature rise
• Particle model


  Helps explain how temperature, pressure, volume and energy in kinetic stores are all related
• Average energy in kinetic stores

  Related to temperature - the higher the temperature, the higher the average energy
• Increasing temperature of a gas

  Increases the average speed of its particles
• Pressure


  The total force exerted by all the gas particles on a unit area of the container walls
• Increasing temperature of a gas

  Increases the pressure (if volume is kept constant)
• Increasing volume of a gas

  Decreases the pressure (if temperature is constant)
• Change in pressure of a gas


  Can cause a change in volume of the container
• Decreasing atmospheric pressure with height

  Causes a helium balloon to expand
• Doing work on a gas

  Increases its internal energy, which can increase its temperature