Thermal and rm^2s

• Temperature


  A number used to indicate the level of hotness of an object on some scale
• Scales of temperature


  • Celsius
  • Thermodynamic (Kelvin)
• The Celsius scale marks the melting point of pure ice as 0°C, and the boiling point of water as 100°C, under atmospheric pressure
• The thermodynamic scale of temperature uses the triple point of pure water, 273.16K and absolute 0 as its fixed points
• Relationship between Celsius and Kelvin

  T(K) = T(°C) + 273.16
• Thermal equilibrium


  When there is no net transfer of thermal energy between two objects
• Solids


  • Atoms are closely packed together
  • Strong electrostatic forces of attraction between molecules
  • Molecules have kinetic energy to vibrate around fixed positions
• Liquids


  • Molecules have greater mean separation than solids
  • Molecules have more kinetic energy to move around
  • Weaker electrostatic attraction than solids
• Gases


  • Molecules have the most kinetic energy to move freely and rapidly
  • Molecules collide elastically with each other
  • Electrostatic attraction between molecules is negligible
• Brownian motion


  Random motion of smoke particles due to collisions with air molecules
• Internal energy


  The sum of the randomly distributed kinetic and potential energies associated with the atoms or molecules which make up a substance
• When a substance is heated but remains in the same state, the kinetic energy of the molecules increases but the potential energy remains the same
• When a substance changes state, the potential energy increases but the kinetic energy remains the same
• The temperature of a substance stays the same whilst it changes phase, because the thermal energy is being used to overcome electrostatic bonds between molecules
• Absolute zero


  0K, the point where all molecules in a substance stop moving completely
• Specific heat capacity


  The energy required per unit mass to increase the temperature by 1K
• Method of mixtures


  Determining specific heat capacity by mixing known masses of substances at different temperatures and measuring the final temperature
• Specific latent heat of fusion

  The energy required per unit mass to change the phase of a substance from solid to liquid
• Specific latent heat of vaporisation

  The energy required per unit mass to change the phase of a substance from liquid to gas
• Mole


  The SI base unit for amount of substance, containing 6.02x10^23 particles (atoms or molecules)
• Assumptions of the kinetic theory of gases

  • Large number of atoms with random, rapid motion
  • Negligible volume of gas atoms compared to total volume
  • Perfectly elastic collisions
  • Negligible collision time compared to time between collisions
  • Negligible electrostatic forces except during collisions
• Pressure


  The sum of the force of each collision between atoms in the gas and the wall, divided by the area of the wall
• Investigating Boyle's law


  Vary volume of gas in sealed syringe, measure pressure, plot pressure vs 1/volume graph
• Estimating absolute zero using gas

  Vary temperature of gas, measure pressure, plot pressure vs temperature graph, extrapolate to find x-intercept
• Root mean square speed

  The square root of the average of the squares of the individual molecular speeds
• Maxwell-Boltzmann distribution


  Shows the number of molecules with each speed, against speed
• Boltzmann constant


  Relates the pressure, volume, number of molecules and temperature of an ideal gas
• The kinetic energy of gas molecules in an ideal gas is proportional to the temperature (in kelvin)
• For an ideal gas, the kinetic energy is equal to the total internal energy, so the internal energy is proportional to temperature