Free expansion of an ideal gas

Click For Summary

Discussion Overview

The discussion revolves around the free expansion of an ideal gas into an evacuated chamber, focusing on the thermodynamic properties involved, such as work, heat, internal energy, temperature, and pressure. Participants explore the implications of these properties and seek to determine the final pressure and temperature of the gas after expansion.

Discussion Character

  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant states that for free expansion, work (W) and heat (Q) are both zero, leading to a change in internal energy (dU) of zero, which implies that the final temperature (T2) equals the initial temperature (T1) of the gas.
  • Another participant suggests that to find the final pressure (P2), additional data about the system is necessary, such as the volume before and after expansion.
  • A participant expresses that they only have the initial temperature and pressure of the gas and seeks help to find the final pressure and temperature.
  • One participant confirms the assumptions made about W, Q, dU, and dT being correct but notes that insufficient data is provided for a definitive answer, as different chamber volumes would yield different results.
  • Another participant proposes that knowing P1 and T1 allows for the calculation of V1, and with V1 and V2, P2 can be determined, provided the volume change is known.

Areas of Agreement / Disagreement

Participants generally agree on the assumptions regarding work, heat, and internal energy, but there is disagreement regarding the sufficiency of the provided data to determine the final pressure and temperature, indicating that multiple views remain on how to approach the problem.

Contextual Notes

The discussion highlights limitations in the available data, particularly the need for information about the volume of the chamber to resolve the final pressure and temperature of the gas.

don_anon25
Messages
35
Reaction score
0
For the free expansion of an ideal gas into an evacuated chamber, I know that Work=0 and Q=0. Correct? This implies that the change in internal energy dU also equals 0. Since U depends solely on T, this should mean that the final temperature of the chamber is equal to the temperature of the ideal gas entering it. But what about the final pressure?
It's an ideal gas, so p1V1=RT1 and p2V2=RT2, but T1=T2, so p1V1=p2V2.
If you could point me in the right direction, that would be very helpful!
 
Science news on Phys.org
You've done all the work. What's the problem?
All you need now in order to find the final pressure, is data on the system. (for example, the temperature, the volume before and after, or any three pieces of data).
 
The problem is that I only have the temperature and pressure of the entering gas, and no other data.
Any ideas?

Here's the actual problem: An ideal gas is allowed to expand freely into an evacuated chamber. The pressure of the entering gas is 5 bar and it has a temperature of 45 degrees Celsius.
Find the final pressure and temperature of the gas.

Are the assumptions I made (that W=0, Q=0, dU=0, and dT=0) correct?
Please help me!
 
Yes, they are. And you need to know one more thing, they haven't given you enough data. (For different chamber volumes, you'll get different results...)
 
Is there a different approach to this problem other than the one I've taken?
I know:
Q=0, W=0, dU=0, p1, and T1=T2.
How do I get p2?
 
With P1 and T1, you work out V1. And with V1 and V2 (you must know how much the gas is expanded in volume) you work P2 out.
 

Similar threads

  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 4 ·
Replies
4
Views
557
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 3 ·
Replies
3
Views
7K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 23 ·
Replies
23
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 22 ·
Replies
22
Views
6K