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Why are isothermal process values higher than adiabatic ones?

  1. Dec 22, 2014 #1
    why are isothermal process values higher than adiabatic process ones?
    I know that the volume is powered by gama in adiabatic process ones, and this has an effect.
    but how can I explain it ?!
    http://www.popsolving.com/Thermodynamics/Problem2.4_Freebody.jpg [Broken]
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Dec 22, 2014 #2

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    What is the defining quality of an isothermal process? What do you need to maintain that quality?
     
  4. Dec 22, 2014 #3
    I want to know why when I draw this relation, the isothermal is above & adiabatic is below. I know this is because of the power "gama"
    Are there any other reasons ?
     
    Last edited: Dec 22, 2014
  5. Dec 22, 2014 #4

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    You're looking at two expansions, an isothermal, and an adiabatic. What's going on in the isothermal expansion that is not going on in the adiabatic expansion?
     
  6. Dec 22, 2014 #5
    ok, sorry i've put the question in wrong meaning.
     
  7. Dec 22, 2014 #6

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    That means you see the difference?
     
  8. Dec 22, 2014 #7
    OK, I want to know why is the adiabatic curve steeper than the isothermal one?
     
  9. Dec 22, 2014 #8

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    What do you have to add to the isothermal process to keep it isothermal?
     
  10. Dec 22, 2014 #9
    I have to make the temperature still constant.
     
  11. Dec 22, 2014 #10

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    Yes. Excellent. And how do you do that?
     
  12. Dec 22, 2014 #11
    I don't know really.
    but may be by closing the system or isolating it ? right ?
     
  13. Dec 22, 2014 #12

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    Wrong. The adiabatic system is closed (no exchange of matter) and insulated, exchanging only work with its surroundings. The isothermal system is closed and not insulated, so it can exchange work and what else with its surroundings?
     
  14. Dec 22, 2014 #13
    The closed system exchange energy with surroundings & the mass is still constant
     
  15. Dec 22, 2014 #14

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    What kind of energy?
     
  16. Dec 22, 2014 #15
    heat or work
     
  17. Dec 22, 2014 #16

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    "Or?" Are you certain it's only one or the other?
     
  18. Dec 22, 2014 #17
    no, the both
     
  19. Dec 22, 2014 #18

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    Okay. Now, compare this to the adiabatic process that can only exchange work with the surroundings.
     
  20. Dec 22, 2014 #19
    That's right !
    In isothermal: Q=W & T is constant , exchange both
    In Adiabatic: Q=0 & W=-ΔU , exchange only work
    Is that right ?!
     
  21. Dec 22, 2014 #20

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    Close enough. The isothermal process picks up extra heat from some external reservoir that maintains the temperature of the working fluid, and that can be converted to work.
     
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