P1.2 - Changes of state

• Particle theory

  Matter is made up of tiny balls (particles) whose arrangement and energy determines the state of matter
• Solid


  • Strong forces of attraction hold the particles close together in a fixed, regular arrangement
  • Particles don't have much kinetic energy, can only vibrate about their fixed positions
• Liquid

  • Weaker forces of attraction between the particles
  • Particles are close together but can move past each other and form irregular arrangements
  • Particles have more kinetic energy than in solids, move in random directions at low speeds
• Gas

  • Almost no forces of attraction between the particles
  • Particles have more kinetic energy than in liquids, are free to move in random directions at high speeds
• Thermal energy store


  Energy held by a substance's particles in their kinetic energy stores
• Heating a liquid

  1. Extra energy passes into the particles' kinetic energy stores, making them move faster

  2. Eventually, when enough particles have enough energy, big bubbles of gas form - this is boiling
• Heating a solid

  1. Extra energy makes the particles vibrate faster

  2. Eventually the forces between them are partly overcome and the particles start to move around - this is melting
• Mass of a substance doesn't change when it changes state, but its volume and density do
• Temperature

  Measure of the average internal energy (thermal energy store) of a substance
• Specific heat capacity

  The change in energy in a substance's thermal store needed to raise the temperature of 1kg of that substance by 1°C
• Measuring the specific heat capacity of a substance

  1. Measure the mass of the substance

  2. Measure the initial temperature

  3. Apply a known amount of energy and measure the temperature increase

  4. Use the formula to calculate the specific heat capacity
• When heating a solid or liquid, energy is transferred to the kinetic energy stores of the particles, making them vibrate or move faster
• When a substance is melting or boiling, energy is used for breaking bonds between particles rather than raising the temperature
• When a substance is condensing or freezing, bonds are forming between particles, which releases energy
• Determining the specific heat capacity of a substance

  1. Rearrange the equation and plug in your measurements

  2. Repeat the experiment at least three times

  3. Calculate the mean specific heat capacity
• Insulating container

  • Reduces the amount of energy that escapes from the sides and bottom of the substance
  • Adding a lid further reduces energy losses
• Heating a solid or liquid

  Transfers energy to the kinetic energy stores of the particles, making them vibrate or move faster
• Melting or boiling

  Energy is used for breaking bonds between particles rather than raising the temperature
• Condensing or freezing

  Bonds are forming between particles, which releases energy
• Specific latent heat


  The energy needed to change the state of 1kg of a substance without changing its temperature
• Types of specific latent heat

  • Specific latent heat of fusion (solid to liquid)
  • Specific latent heat of vaporisation (liquid to gas)