Thermal Physics

• Internal energy is the sum of the randomly distributed kinetic energies and potential energies of the particles in a body
• Kinetic energy is due to the speed of the molecule
• Potential energy is due to the separation between the molecules
• Solids:

  • Regular, fixed structure
  • Cannot move but vibrate (TF vibrational KE)
  • Lowest potential energy -> work needs to be done against forces between particles to separate (as PE 0 at infinity)
• Liquids:

  • free to move but still in contact with each other (vibrational, rotational and translational KE)
  • Higher potential energies than solids
• Gases:

  • Free to move in all directions with high speed (high translational, rotational and vibrational KEs)
  • weak intermolecular forces therefore high potential energy
• The internal energy of a system can be increased by:

  1. Heating -> increased thermal energy, thermal energy transfer
  2. Do work -> to transfer energy as a result of a force moving
• The internal energy of a system can be decreased by:

  1. Lose heat to surroundings
  2. Change in state, gas-> liquid OR liquid -> solid
• When a substance changes state its kinetic energy is constant while its potential energy changes, therefore its internal energy also changes
• Water boiling:

  • Temperature increases up until 100C
  • After which, energy gained through heating is no longer used to increase temperature but instead to break bonds between water molecules
  • Changes state to water vapour and internal energy increased
• LHoV > LHoF as liquid to gas requires more energy than solid to liquid
• Specific latent heat of fusion is the energy required to change a substance from solid to liquid at a constant temperature
• K = C + 273
• A smaller gradient = higher specific heat capacity

  
• Specific heat capacity is the amount of energy required to increase the temperature of 1 kg of a substance by 1°C / 1 K without changing its state
• A lower SHC means it heats and cools quickly.

  e.g. copper = good heat conductor
• Specific latent heat is the amount of energy required to change the state of 1 kg of a material without changing its temperature
• specific heat capacity

  A) energy

  B) mass

  C) change in temperature

  
• Specific latent heat

  A) energy

  B) mass

  
• Units for SHC: Jkg^-1K^-1 or Jkg^-1°C^-1
• Units for SLH: Jkg^-1
• Absolute zero is when the average kinetic energy of the particles is 0 J, it is the theoretical lowest temperature that could ever be reached
• Flow-rate formula: P = m/t x c x change in temp
• Specific latent heat of sublimation is the energy required to change 1kg of a solid to a gas
• Gas laws are empirical, meaning they are derived from experiment, not theory
• 3 gas laws:

  1. Boyle's Law -> pV
  2. Charles' Law -> V/T
  3. The Pressure Law -> p/T
• Boyle's Law:

  • Pressure and volume are inversely proportional
  • p1V1 = p2V2

  A) k

  
• Charles' Law:

  • Volume and temperature are directly proportional
  • V1/T1 = V2T2

  A) k

  
• The Pressure Law:

  • Pressure and temperature are directly proportional
  • p1/T1 = p2/T2
  • When isovolumetric ( const. volume)

  A) k

  
• Boyle's Law:

  • Pressure and volume are inversely proportional
  • p1V1 = p2V2
  • When isothermal (temperature const.)
• Charles' Law:

  • Volume and temperature are directly proportional
  • V1/T1 = V2/T2
  • When isobaric (pressure const.)
• graph

  A) pressure

  B) volume

  C) temperature

  
• 2 graphs

  A) -273

  B) -273

  
• Combined gas law

  • (p1V1)/T1 = (p2V2)/T2

  
• Avogadro's law: Equal volumes of gas at the same temperature and pressure contain equal numbers of particles
• mass of one molecule = mass of one mole / Avogadro's constant (6.022 × 10²³)
• Ideal gas law: pV = nRT

  • n -> number of moles
  • R - > molar gas constant (8.31)
• n = number of moles

  N = number of particles

  NA = Avogadro's constant

  
• pV = NkT

  • N - > number of particles
  • k -> Boltzmann's constant
• k = nR/N = R/NA