Free expansion of an ideal gas.

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Discussion Overview

The discussion revolves around the free expansion of an ideal gas, particularly focusing on the concepts of work done, heat transfer, and temperature changes during the process. Participants explore the implications of the first law of thermodynamics in this context, questioning whether heat (q) is necessarily zero and if the temperature remains constant.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that the work done on the system during free expansion is zero due to the external pressure being zero, but questions whether q is necessarily zero and if the temperature must remain constant.
  • Another participant mentions that the problem is often described as an adiabatic free expansion, suggesting a connection to heat transfer considerations.
  • A third participant states that it is the definition of an adiabatic process, implying that no heat is exchanged with the surroundings.
  • One participant reiterates the need for a mathematical justification for why q is zero in this scenario and questions the relationship between internal energy and temperature for an ideal gas.
  • Another participant acknowledges that while the gas does no work, heat could theoretically flow in or out, indicating uncertainty about the adiabatic nature of the process.

Areas of Agreement / Disagreement

Participants express differing views on whether heat transfer occurs during free expansion and the implications for temperature changes. The discussion remains unresolved regarding the necessity of q being zero and the conditions under which temperature remains constant.

Contextual Notes

There is a lack of consensus on whether the process is strictly adiabatic, and participants highlight the need for further mathematical justification regarding the relationship between heat transfer and internal energy changes.

scorpion990
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I know that the work done on the system in any free expansion is 0 since the external pressure is 0. However.. is q necessarily 0? Does the temperature necessarily stay constant for an ideal gas?

I've been trying to justify the reasons for which q is necessarily 0, but I can't find a reason... Does anybody know why this is so? I know that U varies only with T for an ideal gas, but that would require justifying that the change in temperature is also 0.. does anybody have a mathematical justification for why q is necessarily 0 for a free expansion of an ideal gas?

Thanks.
 
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The problem is usually described as adiabatic free expansion of an ideal gas to address this issue.
 
It's the definition of an adiabatic course
 
scorpion990 said:
I know that the work done on the system in any free expansion is 0 since the external pressure is 0. However.. is q necessarily 0? Does the temperature necessarily stay constant for an ideal gas?

I've been trying to justify the reasons for which q is necessarily 0, but I can't find a reason... Does anybody know why this is so? I know that U varies only with T for an ideal gas, but that would require justifying that the change in temperature is also 0.. does anybody have a mathematical justification for why q is necessarily 0 for a free expansion of an ideal gas?

Thanks.
Apply the first law. Does the gas do work? Does heat flow into or out of the gas from/to the surroundings? What does that tell you about internal energy of the gas?

AM
 
Andrew Mason said:
Apply the first law. Does the gas do work? Does heat flow into or out of the gas from/to the surroundings? What does that tell you about internal energy of the gas?

AM

The gas does no work, but heat could, in theory, flow in or out of the gas. I don't see why it can't... The problem doesn't specifically say that the process is adiabatic, but... I guess it is.. Obviously, that would solve all of the problems.

Thanks everybody!
 

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