Heat absorption in reversible isothermal expansion

Sep 2017
5
0
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:)
 
Apr 2015
1,035
223
Somerset, England
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:
Sep 2017
5
0
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?
 
Apr 2015
1,035
223
Somerset, England
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.