Entropy of gas at constant pressure and volume

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Homework Help Overview

The discussion revolves around the calculation of the overall change in entropy for a gas undergoing two processes: heating at constant pressure and cooling at constant volume. The problem involves specific initial conditions and properties of air, including heat capacities.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of pressure after heating and question the correctness of the derived pressure value. There are attempts to clarify the relationships between temperature, pressure, and volume during the processes described.

Discussion Status

The discussion is ongoing, with participants questioning the assumptions made regarding the processes and the calculations performed. Some guidance has been offered regarding the relationships between variables, but no consensus has been reached on the correct approach or values.

Contextual Notes

Participants are navigating the complexities of thermodynamic processes, specifically distinguishing between isobaric and isochoric conditions. There is mention of using specific equations that may not apply to the current problem context.

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Homework Statement



1m^3 of air is heated reversibly at constant pressure from 288K to 573K. Then it is cooled reversibly at constant volume back to the initial T. Initial P is 103kPa Calculate overall change in entropy.
Cp=1.02
Cv=0.702

Homework Equations



dS=Cp x ln(T2/T1)-R x ln(P2/P1)


The Attempt at a Solution



I have found P2 to be 911kPa but when I put all the data into the above equation I end up with the wrong answer (0.076kJ/K). Please help!

I have found
 
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tell me how u got 911kPa..
its wrong from thr only...
 
I used T2/T1 = (P2/P2)^(n-1/n)

and n = Cp/Cv
 
for 1st proces which is isobaric...
V1/T1=V3/T3... V1= 1m^3 so one can find V3...3 is the intermediate stage
and then for isochoric process...
P3/T3=P2/T2...
n bcoz T2= T1=288 and P3=P1...
n T3=573
so jus find value n den see...
u r goin in wrong direction...dats actually for adiabatic processes
 

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