Kinetic Theory

• Gases


  • Contain particles that are free to move around
  • Collide with the surface of any container
  • Exert a force on that surface, the more frequent the collisions the greater the force
• Absolute zero


  Temperature of -273°C where graphs of Pressure against Temperature and Volume against Temperature reach 0
• Calculating pressure


  1. Pressure = Force / Area

  2. Represents how much force is put onto a specific area

  3. Normally given in units of Pascals (Pa) where 1Pa = 1 N/m2

  4. Can be used to calculate the pressure by a solid on another solid or the force of a gas on a surface
• pV = constant


  Relationship between pressure (p), volume (V) and temperature (T in Kelvin) for a gas
• Pressure and Volume (fixed temperature)

  When volume decreases, pressure increases (inversely proportional)

  Particles have less room to move around and therefore collide with the surface of the container more often
• Pressure and Temperature (fixed volume)

  When temperature increases, pressure increases (directly proportional)

  Particles move around more quickly and collide with the surface of the container more often
• Volume and Temperature (fixed pressure)

  When temperature increases, volume increases (directly proportional)

  Particles move around more quickly and collide with each other more often forcing the particles further apart
• Kelvin scale


  0K = -273°C, 0°C = 273K
• Specific heat capacity


  The energy required to heat 1kg of a substance by 1ºC
• Specific heat capacity of water

  • 4200 J/kg ºC
• Specific latent heat


  The energy required to change the state of 1kg of a substance without a change in temperature
• Specific latent heat of fusion of ice

  • 336000 J/kg
• Temperature changes of a block of ice as it is heated

  1. A-B: Solid

  2. B-C: Melting

  3. C-D: Liquid

  4. D-E: Boiling

  5. E-F: Gas
• Solid


  • Particles are packed very closely, vibrate in place but are not free to move
• Melting


  • Energy is used to break some of the bonds holding the particles in place
• Liquid


  • Particles are close together but can move past each other
• Boiling


  • Energy is used to break all the bonds holding the particles in place
• Gas


  • Particles are free to move and have large gaps between them
• As it is heated

  The particles vibrate more (solid), move past each other more quickly (liquid), move more quickly (gas)
• The energy used for melting is the specific latent heat of fusion
• The energy used for boiling is the specific latent heat of vaporisation, which is larger than the latent heat of fusion because more bonds are broken