5.1 - Thermal physics

• 1st law of thermodynamics

  In a closed system the total energy is conserved
• 2nd law of thermodynamics

  Entropy of the universe increases over time
• 3rd law of thermodynamics

  As we approach absolute zero entropy decreases (gains ordered)
• 5 assumptions with kinetic model

  Large number of molecules moving randomly Molecules volume is small compared to the container Only intermolecular forces during collisions Time between collusion greater than time of collision All collisions are perfectly elastic
• 5 assumptions with kinetic model

  Large number of molecules moving randomly Molecules volume is small compared to the container Only intermolecular forces during collisions Time between collusion greater than time of collision All collisions are perfectly elastic
• 5 ways of transferring Heat

  Particles evaporating Particles diffusing Particles conducting Particles convecting EM radiation
• Absolute zero in Celsius and kelvin

  Celsius-273.15 0 kelvin
• Absolute zero in Celsius and kelvin

  Celsius-273.15 0 kelvin
• An ideal gas

  Gas that obeys the ideal gas laws giving Pv/T
• Avogadro number

  Number of particles within one mole of gas
• Avogadro number

  Number of particles within one mole of gas
• Avogadro number used to convert between

  Mass and number of particles
• Boyles law

  Pressure exerted is inversely proportional to its volume for a fixed mass of gas at constant temperature
• Brownian motion

  The continous and random movement of molecules suspended in a fluid, under a microscope
• Charles law

  The volume of a fixed mass of gas is proportional to the absolute temperature when at a constant pressure
• Charles law

  The volume of a fixed mass of gas is proportional to the absolute temperature when at a constant pressure
• Explain how a gas exerts a pressure on the walls (4 marks)

  Momentum of molecule changes when it collides with the walls Force on the molecule is the rate of change of momentum (2nd law) Force on the wall is equal and opposite to the Force on the molecule Pressure= sum of forces/ area of wall
• Gas

  High speed molecules Assume tiny stored energy Mainly Ek
• Heat transfer

  Energy dissipating from high concentration (hot) to low concentration (cold) regions
• How does Em radiation transfer Heat

  Infrared photons emitted Total rate of Heat loss P=Nhf/t N is number of photons
• How does Particle diffusion transfer Heat

  Collisions between fluid particles cause faster moving particles to move out from their source in random directions
• How does Particles conducting transfer Heat

  Energy transferred by collisions via forces (eg bonds) Good conductors have free electrons
• How does Particles convecting transfer Heat

  Change in density of the fluid, means upthrust. Causes change in height Gravity causes fluid to fall back down
• How does Particles evaporating transfer Heat

  Particles at the surface of a liquid that are given more energy due to collisions are faster enough to escape into the air above So average energy lower so temp lower
• How to convert Celsius to kelvin

  K=T+273
• Internal energy

  The sum of the random distribution of kinetic and potential energies associated with the molecules of a system
• Internal energy of an ideal gas

  Is the sum of each molecules Ek due to its absolute temperature
• Isothermal

  Remains at one temperature during changes
• Isothermal

  Remains at one temperature during changes
• Solids

  Molecules vibrate around a fixed point Internal energy is the Ek of molecules AND the store of negativeenergy
• What does specific mean

  Per kg of matter
• Specific heat capacity

  The energy required to raise the temperature of 1kg of a material by 1 degree Celsius
• Specific heat capacity

  The energy required to raise the temperature of 1kg of a material by 1 degree Celsius
• Specific latent heat 


  The energy required to weaken the bonds between atoms so the material can change state
• State the term used to describe a phase change for a liquid to a gas

  Evaporation
• State the term used to describe a phase change gas to a liquid

  Condensation
• State the term used to describe a phase change liquid to a solid

  Freezing
• State the term used to describe a phase change solid to a liquid

  Melting
• Temperature

  The average kinetic energy of molecules in a system
• Thermal equilibrium

  A state in which there is no net flow of thermal energy between two systems