Talk:Joule expansion

Joule-Kelvin
It is quite wrong that this page redirects to Joule-Kelvin expansion; the processes are distinct and, while similar, very separate!

I shall attempt to rectify this situation immediately, by creating a skeleton article on this subject Landak (talk) 05:28, 11 June 2009 (UTC).

The unsigned comment above is correct and has not been fixed. The statement "If the gas is not ideal, the process is more complex and is called the Joule–Thomson effect" makes it sound like the only difference between the two processes is whether the gas is ideal or not. Retired Pchem Prof (talk) 17:06, 21 January 2016 (UTC)


 * I have replaced the second paragraph with a corrected one that also clarifies the relation between the free expansion thought experiment and the Joule expansion actual experiment. In the process, 3 reference to the Joule-Thomson effect were deleted; I plan to put them in the appropriate article if not already there. Retired Pchem Prof (talk) 20:43, 22 January 2016 (UTC)

Modifications by Adwaele per June 20, 2012
I like the Article, but there was room for improvement, so I changed the Article as listed below. It is a long list, but, basically, they are minor changes.
 * 1) I added a short historical paragraph.
 * 2) The Article switched between 1 mole to n moles. Now it is consistently in n moles.
 * 3) The Article switched between kN and nR. Now all is in terms of nR.
 * 4) I made a clearer distinction between V0, Vi, and Vf.
 * 5) The Sackur–Tetrode equation is now written in a form that it is clearer that the argument of the ln is dimensionless.
 * 6) I added an expression for the entropy in terms of classical thermodynamics.
 * 7) I shortened the discussion about the entropy increase of the universe.
 * 8) Now the article now and then talks about entropy increase instead of entropy change and refers to the concept of entropy production.
 * 9) I changed the notation of work from ΔW to W (work is no function of state) and I made some other typo corrections, definitions of parameters, etc.
 * 10) I added some references.

(Adwaele (talk) 07:51, 20 July 2012 (UTC)).

Parallel Wikipedia article
free expansion is a parallel article. guyvan52 (talk) 16:42, 31 December 2013 (UTC)

How can we merge the two articles?Sellisd (talk) 22:08, 19 July 2018 (UTC)
 * ✅ Klbrain (talk) 11:31, 21 July 2018 (UTC)

Entropy Production
This section seem inappropriate in several ways. Inclusion of the Sacker-Tetrode equation does not seem to serve any purpose. For the most part, this topic is more suitable in the article on Entropy production, which has a section on Entropy production. The description of the reversible isothermal expansion is not not very clear and does not seem to belong here. The entropy change in the process is already discussed at Entropy. The only real relevance of entropy production in a Joule expansion is as an example of calculating the entropy change of the universe during an irreversible process, as mentioned in the last two sentences of the section. That deserves mention here, but details belong elsewhere. Retired Pchem Prof (talk) 17:01, 21 January 2016 (UTC)

Description
I have rewritten the description section to describe the process in general and specifically for ideal and real gases. The old version only really dealt with ideal gas. Retired Pchem Prof (talk) 19:07, 1 February 2016 (UTC)

Speed of the piston
I think, reading between the lines, that the critical thing is that the piston is moved quickly. If it is moved slowly there is work being done. If that is true, it needs to be said explicitly at the beginning, as it is the whole point of the discussion. Tuntable (talk) 10:24, 30 June 2020 (UTC)

One of the worst
This has to be one of the worst written articles Wikipedia contains. First, the lead does not, for some incomprehensible reason, actually describe what is notable about Joule expansion and what it was that Joule found in his experiment!!! Hint: temperature change (or not). (Perhaps discussion of Energy and Entropy as well, I suppose - although Joule couldn't calculate/measure either.) Second, there's a long, long, long section on Entropy. I have no problem following the math, even though it is unnecessarily complex, but I'd guess that most people reading this article will have considerable difficulty. Why is it here? IDK. My problem is the entire section is unjustified. That is, the justification for its inclusion is not presented. IF the importance of Joule expansion is that it demonstrates one of the Laws of Thermodynamics, then it should be OBVIOUS to any editor that that should be clearly stated. Third, and going back to my 1st point, Joule's experiment isn't, as far as I saw, described. Again, it should be obvious that the concrete experiment (as opposed to the ideal (abstract) experiment - both the 'original' and the modern (much more precise and accurate) versions should be presented. (IMHO)174.131.63.209 (talk) 16:07, 12 August 2021 (UTC)