Thermal Physics

• Internal Energy


  Sum of randomly distributed kinetic and potential energies in a gas
• Adding heat increases energy but not always temperature
• Kinetic energy comes from random movements of particles
• Potential energy comes from interactions between particles
• Specific Heat Capacity 


  Energy needed to raise 1KG of material by 1 Kelvin
• Specific Latent Heat


  Energy required to change the state of an object

  -> weakens bonds but doesn't change the temperature
• Absolute Zero


  Lowest possible temperature

  No kinetic energy or vibrations of particles
• 0C = 273 Kelvin
• Ideal Gas Law


  Pressure x Volume = number of moles x ideal gas constant x temperature
• Ideal Gas Constant


  8.31
• Ideal Gas Equation for N Molecules


  Volume x pressure = number of molecules x temperature x Boltzmann Constant
• Avogadro's Number


  Number of molecules in a mole
• Work Done = pressure x change in volume
• Boyle's Law


  At a constant temperature the pressure and volume of gas are inversely proportional
• Charle's Law


  At constant pressure the volume of a gas is directly proportional to its absolute temperature
• Brownian Motion


  First evidence of atoms

  Pollen grains moved in random paths and collided with each other in water
• Pressure


  Molecules colliding with container walls
• Increasing Pressure


  Increase Concentration -> more frequent collisions

  Increase Temperature -> more kinetic energy

  Decrease Container Size -> increase number of collisions
• Kinetic Energy


  Average energy is the same in all directions
• Root Mean Square Speed of Gas Molecules

  Measure of the average speed of gas molecules in a container
• Elastic Collisions in Gas Molecules


  Means that kinetic energy is conserved during collisions
• Key Assumptions of Ideal Gas Model


  • Gas molecules are in constant random motion
  • Collisions between molecules are elastic
  • No intermolecular forces
  • Volume of gas molecules is negligible compared to volume of container
• Implications of Ideal Gas Laws in Thermal Physics


  • Describes behaviour of ideal gasses
  • Relates pressure, volume. temperature and number of moles
  • Useful for calculations
• Total Internal Energy of a Gas


  E = 3/2 nRT
• Gas Expansion


  W = pV
• 1st Law of Thermodynamics


  The change in internal energy of an object is equal to the total transfer of energy due to work done and heating
• Low Specific Heat Capacity = Heats and Cools Quickly
• High Specific Heat Capacity = Heats and Cools Slowly
• Boyle's Law


  pv is constant

  Temperature is fixed
• Charle's Law


  V/T is constant

  Pressure is fixed
• Pressure Law


  p/t is constant

  Volume is fixed
• Pressure Law


  Pressure is directly proportional to temperature
• Calculating Root Mean Square Speed (crms)


  Add squares of each speed and divide by number of molecules