Particle Model of Matter

• Particle theory


  Also known as kinetic theory, helps explain how particles in each state of matter behave
• Particles in solids


  • Strong forces of attraction between them
  • Held close together in a fixed position to form a regular lattice structure
  • Can vibrate around but not flow like a liquid
• Melting of a solid


  1. Particles gain more energy and vibrate more

  2. Forces between particles weaken

  3. At melting point, particles have enough energy to break free of bonds

  4. Solid melts into a liquid
• Particles in liquids


  • Only weak forces of attraction between them
  • Free to move around and arranged randomly
  • Tend to stick together and are fairly compact
  • Have a definite volume even though overall shape can change
• Boiling/Evaporation of a liquid


  1. Particles gain more energy and move around faster

  2. Forces holding particles together weaken

  3. At boiling point, particles have enough energy to break bonds

  4. Liquid boils or evaporates into a gas
• Particles in gases


  • Very weak force of attraction between them
  • Free to move around by themselves
  • Don't keep a definite shape or volume
  • Spread out as much as possible
• Gas particles move in straight lines, not randomly swerving
• Heating a gas


  • Particles travel faster
  • If container is expandable, gas will expand
  • If container is fixed, pressure will increase
• Cooling a gas


  • Particles won't have enough energy to overcome forces of attraction
  • Bonds start to form between particles
  • Gas condenses into a liquid
• Cooling a liquid


  • Particles won't have enough energy to overcome attraction between molecules
  • More bonds form
  • Liquid freezes into a solid
• In a closed system, changes in state don't change the mass, but the density will change
• Density


  A measure of how much mass a substance has per unit of its volume
• Finding density


  Divide mass by volume
• Density formula


  Density = Mass / Volume
• Density is normally measured in kilos per meter cubed in physics
• Density of solids


  • Aluminium: 2.71 grams per centimeter cubed or 2710 kilos per meter cubed
• 1 gram per centimeter cubed

  Equivalent to 1000 kilos per meter cubed
• Calculating volume of a solid given mass and density

  Volume = Mass / Density
• Measuring density of solids


  • Find mass using a balance
  • Find volume of regular shapes by measuring dimensions
  • Find volume of irregular shapes using a Eureka can and measuring cylinder
• Measuring density of liquids


  • Place empty measuring cylinder on balance and zero
  • Pour in known volume of liquid
  • Measure mass of liquid
  • Density = Mass / Volume
• Larger volumes measured give more accurate density results
• Taking multiple measurements helps identify anomalies and calculate a mean
• Specific latent heat


  The energy required to change one kilo of a particular substance from one state to another without changing its temperature
• Heating a substance


  1. Particles gain energy in their kinetic energy store

  2. Increases the internal energy

  3. Increases the temperature
• Temperature is a measure of the average internal energy of all the particles in a substance
• When a substance changes state, the energy provided is used to weaken or break the forces holding the particles together rather than increasing the particle's internal energy
• During state changes, the overall temperature won't change until all of the substance has changed states
• Latent heat


  The exact amount of energy required to change the state of a substance while the temperature remains the same
• Specific latent heat (SLH)


  The energy required to change one kilo of a particular substance from one state to another without changing its temperature
• Types of specific latent heat


  • Specific latent heat of vaporization
  • Specific latent heat of fusion
• Specific latent heat of vaporization


  The energy change when a substance changes between a liquid and a gas (evaporation or condensation)
• Specific latent heat of fusion


  The energy change when a substance changes between a solid and a liquid (melting or freezing)
• The energy required or released is equal to the mass of the substance times the specific latent heat
• Specific latent heat values


  • Specific latent heat of vaporization for water: 2,260,000 J/kg
  • Specific latent heat of fusion for water: 334,000 J/kg
• Heating 1 kg of water from -50°C to 150°C


  1. Particles gain internal energy, temperature increases

  2. At 0°C, ice starts to melt, energy used to break forces between particles, temperature stays constant

  3. Once all ice has melted, temperature continues to increase

  4. At 100°C, water starts to boil, energy used to break forces between particles, temperature stays constant

  5. Once all water has boiled, temperature continues to increase
• You don't need to memorize the specific latent heat values, they will be provided in the exam if needed
• Particles in gases


  • Free to move about in completely random directions
  • Rebound and carry on in a different direction when they hit a wall
  • Exert a force whenever they collide with the walls of the container
• Pressure


  The force being exerted per unit of area or the force divided by the area
• Factors that determine pressure


  • Number of collisions
  • Energy of each collision
• Heating up the gas


  • Transfers energy to the particles, increasing their kinetic energy
  • Particles move around faster
  • More collisions with the walls
  • Each collision involves more force
  • Pressure increases