Talk:Relations between heat capacities

Relations between specific heats

Since Relations between specific heats redirects here, I included corresponding relations between specific heat capacities (c_v and c_p) also in this article, mentioning which heat capacities are extensive and which are intensive properties. H Padleckas (talk) 13:09, 10 March 2009 (UTC)

I don't have my copy of Atkins handy but this is the first place I would look here is the citation for the current addition if anyone can check to see if if contains this content.Atkins, Peter (2002-01). Atkins' Physical Chemistry (7th ed.). Oxford University Press. ISBN 0198792859. {{cite book}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help). Doesn't this material belong on the heat capacity page? This is very close to textbook material and WP:NOTTEXTBOOK.--OMCV (talk) 22:52, 16 September 2009 (UTC)

The derivation of C_p - C_V can be found in he book by F. Reif. The derivation of C_P/C_V isn't there, perhaps in Atkins or in some other textbook. But then I don't think it is not so relevant, because even if a derivation can be found, it may not be the same as presented here and it may not be preferable to have the same derivation.

The heat capacity page gives a general description of what heat capacity is, it links to this page for the two derivations. And not everyone agrees with the policy WP:NOTTEXTBOOK. Many of my larger contributions to wikipedia have been text-book style mathematical derivations, e.g. of Planck's law, Stefan-Boltzmann's law, Helmholtz-free energy, fundamental thermodynamic relation etc. etc. etc. I know many Wikipedians do not like my edits, but I see Wikipedia evolving from a stupid encyclopedia containing only simple factoids to a fully self-contained repository of all knowledge. Count Iblis (talk) 23:08, 16 September 2009 (UTC)

I sympathize with much of what you say but I think you need to consider the big picture and why WP:OR is so valuable. With all that said I think you need to at least cite a source where the underived relationship can be found. So a future student can follow ciations back to the orginal source.--OMCV (talk) 23:43, 16 September 2009 (UTC)

One: I fail to see without any citations how this is notable, or just a list of equations derived and posted on WP WP:NOTTEXTBOOK. Two: if you don't want to stand by WP:VERIFY, then maybe you shouldn't be editing WP and focus on more scholarly pursuits. Angryapathy (talk) 16:01, 1 October 2009 (UTC)

If you fail to see that this is a closely reasoned mathematical derivation and just see this as a "list of equations", you are not qualified to comment here. I could just as well go to the Chinese Wikipedia and comment there that all the articles there are a string of Chinese characters. Count Iblis (talk) 16:22, 1 October 2009 (UTC)

Style of presentation

I am not too worried about the referencing issue; any basic material from thermodynamics will be, in principle, sourceable to numerous textbooks. I did add one reference just to start the process and establish a referencing style.

I am more worried about the style of the prose. The article reads like a textbook; it is not clear to me what the overall point of the article is, beyond carrying these derivations. In general we have a preference against articles like that. But I think this might be fixed by adding to this page a more general discussion of the relationships between the capacities, instead of simply the derivations. Then we would actually have something that we can call an article with a straight face. — Carl (CBM · talk) 17:22, 1 October 2009 (UTC)

This article is referenced from a few other articles on heat capacity, and I think also from the internal energy article, so it functions a bit like an appendix. In some other articles, I've included derivations as appendices or directly in the articles themselves, e.g.:

Tachyonic antitelephone

Stefan–Boltzmann law

Planck's law

Helmholtz free energy

Joule–Thomson effect

Second law of thermodynamics#Proof of the Second Law Count Iblis (talk) 17:41, 1 October 2009 (UTC)

I wasn't clear; I meant the purpose of the article may not be clear to a random reader who arrives here from the "random article" button. — Carl (CBM · talk) 20:37, 1 October 2009 (UTC)

I think the "style" the article is written in can be changed from a tutorial-like tone to a more encyclopedic tone, yet still keeping the same information. Someday when I have nothing to do, I may have a go at it. H Padleckas (talk) 20:00, 1 October 2009 (UTC)

Yes, I am certain that the style/tone/whatever can be improved at some point as information is added to the article. And I am not trying to force anyone to do it right now. It's just something to keep in mind as the article develops over time. — Carl (CBM · talk) 20:37, 1 October 2009 (UTC)

User:Kbrose has edited the "style" to improve it from a tutorial-like tone to a more encyclopedic tone... Thank you, Kbrose. H Padleckas (talk) 00:51, 21 May 2014 (UTC)

NPOV/Accuracy

See [1]. The tags should remain until this is clarified. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 01:28, 22 February 2010 (UTC)

No. Count Iblis (talk) 01:31, 22 February 2010 (UTC)

Reasoning in derivation?

In the derivation section, I'm having difficulty following the step from the fourth to the fifth equation. The fourth equation is derived under the assumption of constant pressure. However the fifth equation assumes constant volume. How can the latter follow from an equation that depends on constant pressure unless both pressure and volume are constant? But how can both pressure and volume remain constant when the temperature is changing?

I'm not questioning the conclusion of the derivation, only its reasoning. I would be more comfortable with a derivation that made physical sense at every intermediate step, not just at the end. Vaughan Pratt (talk) 19:19, 30 October 2013 (UTC)

Ah, I think I get it. I had misinterpreted "If the only external variable of the system is the volume" as meaning that the other external variable, namely pressure, was being held constant. What it actually means is that the only external variable, volume, is assumed to be a function of pressure which is not considered an external variable for this purpose. If my interpretation is correct then the concept of pressure being a relevant variable that is nevertheless not external needs to be clarified somehow. If it's not correct then the correct interpretation needs to be supplied. As it stands it's confusing. Vaughan Pratt (talk) 19:29, 30 October 2013 (UTC)

Maybe a simpler interpretation is that PV/T is constant whence it suffices to vary only T and one of V or P in order to determine the variation of the remaining variable. Vaughan Pratt (talk) 06:15, 31 October 2013 (UTC)