physics final

• Work


  The work done on or by a thermodynamic system
• Thermal Processes for closed systems


  • Isobaric
  • Isovolumetric/Isochoric
  • Isothermal
  • Adiabatic

  
• 1st Law of Thermodynamics


  ∆U = Q - W
• Q


  Energy exchanged between the gas and the environment
• W


  Work done on/by the gas
• ∆U

  Internal energy of the gas (sum of kinetic and potential energies of particles)
• Quasi-static process


  • Occurs slowly enough that a uniform pressure and temperature exists throughout the whole system at all times

  
• Isobaric process


  Pressure remains constant
• Isochoric/Isovolumetric process


  Volume remains constant
• Isothermal process


  Temperature remains constant

  
• Adiabatic process


  No heat is exchanged between the gas and the environment

  
• 2nd Law of Thermodynamics


  Defines how spontaneous processes occur
• Most processes are irreversible - they only happen in one direction
• 1st definition of 2nd Law of Thermodynamics


  Heat transfer occurs spontaneously from hotter objects to colder objects (never from cold to hot)

  
• Heat engine


  • Uses heat to perform work and has 3 essential features: 1) Heat QH is supplied from hot object at TH, 2) Part of input heat is used to do work W, 3) Remaining heat QC is expelled to cold object at TC

  
• 2nd definition of 2nd Law of Thermodynamics


  It's impossible for any system to completely convert heat into work during a cyclic process
• Thermal efficiency of a heat engine


  e = W/QH = 1 - QC/QH

  
• Reversible process


  The gas can be returned to its initial state (no spontaneous heat transfers)
• Carnot engine


  Idealized, maximum-efficiency cyclical engine for reversible processes
• Carnot efficiency


  eC = 1 - TC/TH
• 3rd definition of 2nd Law of Thermodynamics

  A Carnot engine will always have a greater efficiency than any other heat engine operating between the same temperatures, and any reversible Carnot engine will always yield the same maximum efficiency for the given operating temperatures
• Entropy


  A measure of the disorder of a system
• Entropy change for a reversible process


  ∆S = Q/T
• 4th definition of 2nd Law of Thermodynamics


  Any reversible process cannot change the entropy of the universe; any irreversible process causes the entropy of the universe to increase (∆S ≥ 0)
• Specific Heat


  Quantify the amount of heat required to change the temperature of an object

  
• Calorimetry


  Learn how insulating materials are used to exchange heat between multiple objects

  
• Latent Heat


  Quantify the amount of heat required to change the phase of an object

  
• Thermal Processes


  Learn how heat is exchanged between objects through convection, conduction, and radiation

  
• Heat (Q)


  The spontaneous transfer of energy between a system and its environment due to a temperature difference

  
• Example of heat transfer


  • An ice cube in a cup of warm water – the ice cube is the system, while the cup and warm water is the environment
• Units of heat


  Joules or calories (1 cal = 4.186 J)

  A Calorie describes the energy content in foods, and is related to the calorie: 1 Cal = 1000 cal = 1 kcal
• Specific Heat (c)


  The energy Q transferred to a mass m will change its temperature by ΔT

  c ≡ Q/mΔT or Q = mcΔT

  
• If ΔT > 0 (the substance gets warmer): Q > 0 → energy flows into the system

  
• If ΔT < 0 (the substance gets colder): Q < 0 → energy flows out of the system
• Calorimeter


  An insulated container that prohibits heat transfer to the outside environment

  Used to measure the specific heat capacities of unknown substances

  
• Calorimetry


  The qualitative measure of heat exchange

  
• By conservation of energy: Σ Qgained = Σ Qlost or Σ Q = 0
• Phases Changes of Matter


  Melt: solid → liquid

  Freeze: liquid → solid

  Evaporation: liquid → gas

  Condensation: gas → liquid or gas → solid

  Sublimation: solid → gas

  
• During a phase change, the temperature of the object will not change (as long as it's in thermal equilibrium). Only the internal energy will change.

  
• Latent Heat (L)


  The energy Q required to change the phase of a material of mass m

  Q = mL