Entropy of gas at constant pressure and volume

AI Thread Summary
The discussion focuses on calculating the overall change in entropy for a gas undergoing two processes: heating at constant pressure and cooling at constant volume. The initial conditions include 1m³ of air heated from 288K to 573K at 103kPa. The user initially calculated the final pressure after heating to be 911kPa but received an incorrect entropy change result. Other participants pointed out the misuse of equations applicable to adiabatic processes rather than the correct approach for isobaric and isochoric processes. Clarification on the correct application of thermodynamic principles is emphasized to resolve the calculation errors.
ricof
Messages
14
Reaction score
0

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
 
Physics news on Phys.org
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
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

The specific work done on an ideal gas during an adiabatic process in a piston-cylinder system
Replies
13
Views
951
Gas temperature in a constant volume
Replies
8
Views
2K
Open Gas Turbine - calculate T2, T3, T4, efficiency
Replies
1
Views
2K
Solving Unusual Problems: Using the Polytropic Ideal Gas Equation
Replies
5
Views
1K
Adiabatic Expansion of Pressurized Air in a Piston-Cylinder Setup
Replies
8
Views
2K
Change in entropy of an irreversible adiabatic process
Replies
3
Views
1K
Change in entropy of an ideal gas during thermodynamic cycle
Replies
1
Views
2K
Trouble solving for end state of two control volumes in a rigid tank
Replies
12
Views
2K
Finding the pressure of a gas in three identical balloons
Replies
12
Views
2K
Proof question related to the Ideal Gas Law
Replies
8
Views
2K

Hot Threads

Recent Insights

Back
Top