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Review. What is the word for “movement of heat”? Thermodynamics 2) The phrase “energy cannot be created nor destroyed” is know as The law of conservation of energy. Review. 3) What is the rest of the phrase (for the conservation of energy) ?

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Review

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  1. Review • What is the word for “movement of heat”? Thermodynamics 2) The phrase “energy cannot be created nor destroyed” is know as The law of conservation of energy

  2. Review 3) What is the rest of the phrase (for the conservation of energy) ? It simply transforms into another form of energy 4) If you add energy to a system it does one of 2 things…

  3. Review 1) increase the internal temperature 2) does external work Ht added=↑ internal energy + external work done

  4. 2nd Law of Thermodynamics- Thisis the one that prevents you from building a perpetual motion machine (motion that continues indefinitely without any external source of energy)

  5. 2nd Law of Thermodynamics Clausius Statement Kelvin-Planck Statement • This implies that it is impossible to build a heat engine that has 100% efficient

  6. Changing Work (Fxd) Completely Into Heat is Easy • 1) Rub your hands together quickly • 2) Push a box across the floor

  7. Changing Heat Completely Into Work (Fxd) Can Never Happen • The best that can happen is to convert some heat into mechanical work • The first steam engine to do this was invented in 1700

  8. Engines and the 2nd Law Today steam turbines generate about 90% of the electric power in the United States using a variety of heat sources

  9. Engines and the 2nd Law • The average automobile engine is only about 35% efficient, and must also be kept idling at stoplights, wasting an additional 17% of the energy, resulting in an overall efficiency of 18%

  10. Lightbulbs • Incandescent lightbulbs are 3% efficient, fluorescent 10% ….mini-heaters…..CFLs (compact fluorescent lights) are 70 % efficient

  11. 3rd major concept in the 2nd law of Thermodynamics…Entropy

  12. Entropy- ordered energy tending to disordered energy For natural processes, entropy always increases

  13. Entropy however, when there is work input (as in living organisms) entropy decreases

  14. ….in a nutshell-the 2nd Law of Thermodynamics • 1) Heat flows from a hot body to a cool one • 2) Heat cannot be completely converted to work • 3) Every system becomes disordered over time

  15. The laws of thermodynamics are sometimes stated this way 1) You can’t win 2) You can’t break even 3) You can’t get out of the game 1) b/c you can’t get any more energy out of a system than you put in 2) b/c you can’t even get as much energy out as you put in 3) Entropy in the universe is always increasing

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