Quick question about pressure in gases.

  • Thread starter Thread starter Beer-monster
  • Start date Start date
  • Tags Tags
    Gases Pressure
Click For Summary
SUMMARY

The discussion centers on the calculation of final pressure in a vessel containing two gases at different initial pressures, P1 and P2. The correct formula for the final pressure, P_f, is derived using Boyle's Law: P_f = (P1V1 + P2V2) / (V1 + V2), which accounts for the volumes of the gases. The user also seeks assistance in simplifying the entropy change formula, ΔS = nR ln(P1P2 / P_f²), to express it in terms of P1 and P2. The importance of volume and temperature in pressure calculations is emphasized.

PREREQUISITES
  • Understanding of Boyle's Law
  • Knowledge of gas laws and thermodynamics
  • Familiarity with entropy and its calculations
  • Basic algebra for manipulating equations
NEXT STEPS
  • Study the derivation of Boyle's Law and its applications in gas behavior
  • Learn about the relationship between pressure, volume, and temperature in ideal gases
  • Explore entropy calculations in thermodynamics, particularly for mixing gases
  • Investigate advanced topics in statistical mechanics related to gas mixtures
USEFUL FOR

This discussion is beneficial for students and professionals in physics, chemistry, and engineering, particularly those focusing on thermodynamics and gas behavior in various applications.

Beer-monster
Messages
285
Reaction score
0
Two gases are in a vessel and separated by a partition. They start at different pressures P1 and P2. When the partition is removed and equilibrium restored am I right in thinking the new pressure is the average of the starting pressure i.e.

[tex]P_{f} = \frac{P1+P2}{2}[/tex]

Thanks.
 
Physics news on Phys.org
Nope. Volume and temperature count, too.

What would happen if one side of the vessel contained a thimble full of gas at 100 Pa, and the other side contained a tanker car full at 50 Pa? Would an average make sense?
 
Okay using Boyle's Law I get:

[tex]P_{f}=\frac{P1V1+P2V2}{(V1+V2)}[/tex]

If this is correct, I have the slight problem that my work for the full question (calculate the entropy change when the gases mix) end with:

[tex]\Delta S = nR \ln\left(\frac{P1P2}{P_{f}^{2}}\right)[/tex]

Substituting the first expression in gives a mess, which I can't seem to simplify to give an expression in terms of P1 and P2. Anyone poke me in the right direction?
 

Similar threads

Replies
4
Views
3K
  • · Replies 4 ·
Replies
4
Views
1K
Replies
16
Views
4K
Replies
3
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
3
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 13 ·
Replies
13
Views
3K