Hi guys, i have a quick question about thermodynamics. If i have

hjelp

APEPE

>>8611523
You can if you justify the behavior of the gas for the give temp and pressure changes.

If it doesn't compress normally or transfer heat, you'd have to derive new kinematics to get a modified law.

From there, you can use the divergence to find a new value for S

>>8612032
The process is isobaric, so the pressure stays the same. I'm not interested in the process itself but in how much the entropy does change. The formula which i posted before can be obtained via the clausius integral and the ideal gases law. I'm asking if i can use it for non-ideal gases too.

>>8611523
no, deriving that equation assumes an ideal gas.
[eqn] \Delta S = \int \frac{dQ}{T}[/eqn]
with
[eqn] Q = \Delta U + P\Delta V[/eqn]
since its isobaric. Also
[eqn] \Delta U = nc_V \Delta T[/eqn]

Now since its an ideal gas let [math] P\Delta V = nR\Delta T[/math] and you get
[eqn] Q = nc_V \Delta T + nR\Delta T = nc_P \Delta T[/eqn]

Putting that in the integral gives
[eqn] \Delta S = \int nc_P \frac{d T}{T} = nc_P \ln\frac{T_1}{T_2}[/eqn]

Now if its not an ideal gas:

Lets say [math] PV = f(T)[/math] for some function, well get
[eqn] \Delta S = \int nc_V \frac{d T}{T} + \int \frac{f'(T)d T}{T}[/eqn]
In general.

>>8611523
Just use P=nRT/V

>>8614035
You don't need to use the ideal gas equation to derive that formula. Only to assume that the molar heat capacity is constant. By the definition of heat capacity:
[math]\delta Q=nc_pdT[/math]
So:
[math]\Delta S=\int nc_p\frac{dT}{T}[/math]