Educator

Thermodynamics

• The first law of thermodynamics states that the amount of heat put into a system is equal to the change in the system's internal energy and the work the system does:
  

  Q = ∆Einternal + W.

• An engine is a clever way to convert heat into work.
• The second law of thermodynamics states that heat always flows from hot objects to cold objects (unless external work is put in).
• Entropy is a measure of chaos and disorder: how random the exact configuration of a system is.
• We can re-state the second law of thermodynamics as, "For all processes, entropy either increases or remains the same. It never decreases." Why does this mean the same thing? Temperature is random, vibratory motion. If we spread this motion out over more objects, we've spread out the randomness over more possibilities, increasing our total randomness.
• Ordered systems tend to disorder. Systems that increase their own order must do it by causing even greater disorder elsewhere.
• For an engine, efficiency (ε) is a measure of how much work we get out for the heat we put in:
  

  ε = W Q = energy we get out energy we put in .

• It is impossible for an engine to have 100% efficiency (i.e., ε = 1.00).
• A Carnot engine is a theoretical engine with the maximum possible efficiency. Its efficiency depends on how hot the heat source is and how cold the the sink/exhaust is:
  

  εmax, carnot = 1 − Tcold Thot .