C4 Heat

• Thermal Equilibrium is achieved when two objects in thermal contact are at the same temperature and there is no net heat transfer.
• S.I unit for heat is joule, J.
• Heat is energy transferred from one object to another due to difference in temperature.
• Heat capacity, C is the quantity of heat required to raise the temperature of object by 1 degree celsius.
• S.I unit for Heat Capacity is joule per kelvin.
• Specific Heat Capacity is the quantity of heat required to raise the temperature of 1kg of substance by 1 degree celsius.
• S.I unit for Specific Heat Capacity is joule per kilogram per kelvin.
• Heat Capacity depends on

  • mass of substance; different masses of same substance have different heat capacities
  • type of substance; equal masses of different substances have different heat capacities
• The specific latent heat of fusion (Lf) is the quantity of heat, Q absorbed during melting or released during freezing of 1 kg of substance without any change in temperature.
• The specific latent heat of vaporisation (Lv) is the quantity of heat, Q absorbed during boiling or released during condensation of 1 kg of substance without any change in temperature.
• Latent heat is the thermal energy absorbed or released by a substance during change of state with no change in temperature.
• Latent heat of fusion is the amount of heat

  • absorbed during melting
  • released during freezing
• Latent heat of vaporisation is the amount of heat

  • absorbed during boiling or evaporation
  • released during condensation
• Solid:

  • fixed shape, mass, volume
  • high density
  • not compressible
  • small space around particles
  • very close and in order
  • vibrate in fixed positions
  • strong FOA
• Liquid:

  • follow shape of container
  • fixed mass, volume
  • medium density
  • difficult to compress
  • moderate space around particles
  • close but not in order
  • moving randomly and sliding over
  • weak FOA
• Gas:

  • follow shape of container
  • fixed mass, volume
  • low density
  • compressible
  • large space around particles
  • far from one another
  • moving randomly and freely
  • very weak FOA
• Absorption of latent heat of fusion during melting:

  1. particles are held together by strong molecular bond
  2. energy is absorbed to break the bond
  3. does not change kinetic energy or temperature
• Absorption of latent heat of vaporisation during boiling:

  1. particles are held together by weak bond
  2. energy is absorbed to break molecular bond
  3. does not change kinetic energy or temperature
• Evaporation by Kinetic Theory:

  • molecules move randomly at different speeds with different kinetic energies
  • evaporation occurs when faster moving molecules overcome FOS between other molecules to escape into the air
  • slower moving molecules are left behind
  • causes average speed and average kinetic energy to decrease
  • temperature decreases and cooling occurs
• Kinetic Theory of Gasses: gas molecules are constantly moving randomly and freely, and colliding with one another with the wall of the container.
• Boyle's Law: pressure is inversely proportional to volume for a fixed mass of gas at constant temperature

  • temperature is constant
  • PV = constant
  • P1V1 = P2V2
• Charles' Law: volume is directly proportional to absolute temperature of a fixed mass of gas at constant pressure

  • pressure is constant
  • V/T = constant
  • V1/T1 = V2T2
• Gay-Lussac's Law: pressure is directly proportional to absolute temperature of a fixed mass of gas at constant volume.

  • volume is constant
  • P/T = constant
  • P1/T1 = P2/T2