Entropy of gas at constant pressure and volume

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SUMMARY

The discussion focuses on calculating the overall change in entropy for 1m³ of air heated reversibly at constant pressure from 288K to 573K and then cooled reversibly at constant volume back to the initial temperature. The relevant equations include the entropy change formula, dS = Cp x ln(T2/T1) - R x ln(P2/P1), where Cp is the specific heat at constant pressure. The participants identified an error in calculating P2, which was found to be 911kPa, and clarified that the approach used for calculating n should be based on isobaric processes rather than adiabatic processes.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically entropy and its calculation.
  • Familiarity with the ideal gas law and its applications.
  • Knowledge of specific heat capacities, Cp and Cv, and their significance in thermodynamics.
  • Ability to manipulate logarithmic equations in the context of thermodynamic calculations.
NEXT STEPS
  • Study the derivation and application of the entropy change formula in thermodynamics.
  • Learn about the ideal gas law and its implications for pressure, volume, and temperature relationships.
  • Explore the differences between isobaric and isochoric processes in thermodynamic systems.
  • Investigate the concept of reversible processes and their significance in calculating thermodynamic properties.
USEFUL FOR

Students and professionals in thermodynamics, mechanical engineers, and anyone involved in heat transfer and energy systems will benefit from this discussion.

ricof
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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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