4-6 Heat and Temperature

• expand means substances ability, to increase in volume
• contract means the ability of a substance to shrink or decrease in volume
• particles expand when heated and contract when cooled
• solids

  • have definite shape and volume
  • cannot be compress
• liquids

  • have definite volume but no definite shape
  • cannot be compressed
• gases

  • have no definite shape and volume
  • can be compressed
• when materials warm up, particles move faster and spread out (expand)
• when materials cool down, particles slow down and decrease in volume (contract)
• gasses expand more than solids when temperature changes
• different materials expand and contract at different amounts at different temperatures
• heat capacity is the amount of thermal energy that warms or cools the object by 1 degree it depends on the material and mass
• specific heat capacity is the amount of thermal energy that warms or cools one gram of a material by degree Celsius depends on material and mass
• melt


  turn from solid to liquid
• freeze


  change from a liquid to a solid
• evaporate


  process which a liquid changes into a gas or a vapour
• condense


  change from a gas or vapor into liquid
• sublimation


  a change in state from gas to solid or solid to gas ex. carbon dioxide
• evaporative cooling


  a process in which the faster moving particles on the surface of a liquid evaporate and escape into the air
• the temperature stays the same the speed of the particles cannot be changing because the temperature stays constant during phase change. if the speed of the particles changed the temperature would have to change too
• radiation

  • they behave like waves
  • they can be absorbed and reflected by objects
  • they travel across empty space at the same very high speed: 300 000 km/s
• shiny surfaces and white colored surfaces like aluminum foil reflects heat the best
• dull and black coloured objects absorb heat the best, and white and shiny objects absorb the least
• thermal conduction is the direct transfer of thermal energy from one particle or object to another through contact or collision
• heat insulators are materials that do not conduct heat well, so they are used to keep warmth in
• heat insulators are materials that slow the transfer or conduction of thermal energy from object to another
• convection is a process by which a warm fluid moves from one place to another
• energy source: energy that is transferred from one store to another, usually by burning a fuel
• when items heat up, generally they expand as the particles move faster and the volume increases
• when an item cools down the particles slow down and the volume contracts
• energy source


  where the energy is originally stored
• direction of energy transfer

  from high concentration to low concentration
• transformations


  as energy is moved to a new part of the system, it may be placed in a different store
• waste heat


  most systems transfer at least a little energy to the thermal store of the surroundings
• control system


  ways of adjusting energy transfers to keep the energy in control
• land cools down faster then water
• water has a higher heat capacity then land
• heat capacity is how much energy needs to be transferred into an object to raise its temperature by one degree celsius
• metal is a good conductor of heat and electricity because it has delocalised electrons that can move freely
• glass and wood are poor conductors but good insulators
• insulation stops heat from escaping or entering