Physics Help Forum Heat absorption in reversible isothermal expansion

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 Oct 2nd 2017, 11:52 AM #1 Junior Member   Join Date: Sep 2017 Posts: 5 Heat absorption in reversible isothermal expansion 2kgs (total mass) of steam goes through a revesible isothermal expansion at 500 degrees celcius. During the expansion the pressure drops from 300 kpa to 200 kpa What is the heat absorbed by the steam during this process? I guess that steam cannot be assumed to be ideal which makes the problem more difficult:S Would appreciate some help or pointers
 Oct 2nd 2017, 12:24 PM #2 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 735 You need to decide which PV relationship to use. That will allow you to calculate the work done in the expansion. What does the first law say about the heat absorbed in relation to the work done, when the expansion is isothermal? Last edited by studiot; Oct 2nd 2017 at 12:54 PM.
 Oct 2nd 2017, 05:01 PM #3 Junior Member   Join Date: Sep 2017 Posts: 5 In a isothermal expansion: there is no change in internal energy so it is 0 and the work is done by the system so W is positive Q=+W I reckon i cannot use the w=nRTln(vf/vi)? What PV relationship am i supposed to use?
Oct 3rd 2017, 06:25 AM   #4
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Join Date: Apr 2015
Location: Somerset, England
Posts: 735
 Originally Posted by zwambooo In a isothermal expansion: there is no change in internal energy so it is 0 and the work is done by the system so W is positive Q=+W I reckon i cannot use the w=nRTln(vf/vi)? What PV relationship am i supposed to use?
Why can't you use that equation?

PV = a constant is exactly the relationship you should be using for a reversible isothermal expansion.

Since the whole process takes place at 500C the steam is dry steam throughout.

 Tags absorption, expansion, heat, isothermal, reversible, steam

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