Chemistry Help with this interpolation (change in entropy while heating water)

AI Thread Summary
The discussion revolves around the challenges of interpolating entropy values for water at specific pressures and temperatures. The user encounters a problem with the absence of data for 25 psia in the superheated water table, leading to confusion about the interpolation process. It is clarified that the final state is a mixture of saturated liquid and vapor at 240 F and 25 psi, not superheated. The correct approach involves calculating the mass fractions of liquid and vapor to determine the combined entropy, rather than relying solely on the saturated water table. Proper interpolation is essential to accurately resolve the entropy change during the heating process.
Noob of the Maths
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Homework Statement
A piston-cylinder device initially contain 7 lbm of liquid water at 25 psia and
75 F the water is now heated at constant pressure by the addition of 4520
Btu of heat. Determine the entropy change of the water during this process.
Relevant Equations
Heat and pression
Hello, everyone :).
I try to resolve this common problem. But, when i got in the interpolation of state 2, the values not make the sense.
I have 25 psia and 75 F, but, in the superheated water table, there are not values with 25 psia (only 20 psia and 40 psia). And, the temperature values starting with 1000 F, so, its not possible the interpolation.

Captura de Pantalla 2021-09-17 a la(s) 4.34.55.png

Thanks for read!
 
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The final state is not superheated. It is a combination of saturated liquid and saturated vapor at 240 F and 25 psi.
 
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Chestermiller said:
The final state is not superheated. It is a combination of saturated liquid and saturated vapor at 240 F and 25 psi.
So, i can use the saturated water table and use the 240 F with that 24.985 psia, and just use btu/lbm *R of the Sfg? In this case interpolation its not necessary?
Captura de Pantalla 2021-09-17 a la(s) 13.50.00.png
 
Noob of the Maths said:
So, i can use the saturated water table and use the 240 F with that 24.985 psia, and just use btu/lbm *R of the Sfg? In this case interpolation its not necessary?
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No way. You need to find the mass fraction liquid and the mass fraction vapor in the final state, and then use this to get the combined entropy in the final state.
 
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