Topic 3 - particle model of mattter

• 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
• Heating up a solid

  1. Particles gain more energy

  2. Vibrate even more

  3. Forces between them weaken

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

  5. 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
• Heating up a liquid

  1. Particles gain more energy

  2. Move around faster

  3. Forces holding particles together weaken

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

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


  • Force of attraction between them is very weak
  • Free to move around by themselves
  • Don't keep a definite shape or volume
  • Spread out as much as possible
• Gases are constantly moving with random motion, meaning they travel in straight lines but get deflected randomly by walls and other particles
• Heating up a gas

  1. Particles gain more energy and travel faster

  2. If container is expandable, gas will expand

  3. If container is fixed, pressure will increase
• Cooling down a gas

  1. Particles won't have enough energy to overcome forces of attraction

  2. Bonds start to form between particles

  3. Gas condenses into a liquid
• Cooling down a liquid

  1. Particles won't have enough energy to overcome attraction between molecules

  2. More bonds form

  3. Liquid freezes into a solid
• In a closed system, changes in state won't change the mass, but the density will change (solids highest, liquids slightly lower, gases lowest)
• converting  g/cm3 to kg/m3 

  Multiply the g/cm3 value by 1000
• 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
• Calculating density of a solid experimentally

  1. Find mass

  2. Find volume (regular shape: measure dimensions, irregular shape: use Eureka can)
• Calculating density of a liquid experimentally

  1. Place empty measuring cylinder on balance and zero

  2. Pour in liquid (e.g. 10 ml)

  3. Measure mass of liquid

  4. Density = Mass / Volume
• Larger volume measurements 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 internal energy

  3. Increases 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
• Heating 1 kg of water from -50°C to 150°C

  1. Particles gain internal energy, increasing temperature

  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
• Particles in gases behave

  1. Particles move about in random directions

  2. Particles rebound off walls and carry on in different directions
• Pressure


  The force being exerted per unit of area
• Particles colliding with walls of container

  Create pressure
• Factors determining pressure


  • Number of collisions
  • Energy of each collision
• Increasing temperature


  Increases pressure
• Increasing concentration


  Increases pressure
• Decreasing volume


  Increases pressure
• Flexible container


  Changes in temperature and concentration change the volume rather than the pressure