Talk:Critical point (thermodynamics)

Merge
I don't think that critical point drying should be merged into this article. It is a big enough topic to support an article of its own. Of course, the article in its present state is pretty bad. Hopefully it will be fixed up soon. -- Kjkolb 09:51, 10 February 2006 (UTC)

Changing image size
In my opinion, the image is oversized and should be smaller. I do not know how to do so, can anyone do it?

Table
Some values in the table are listed in Kelvin (water 370 something), others in Celsius. Table lists them as Celsius.

New section on chaotic instabilities
This subject seems to focus on chemical critical points wrt temperature and phase changes of homogeneous stuff. But shouldn't it also include the criticality associated with limit cycles of systems far from equilibrium (i.e., dissipative systems)? Just a thought. If I knew more I would put it in. Rhetth (talk) 14:59, 13 August 2009 (UTC)


 * I think this is some other critical point not thermodynamic critical point. Generally one is talking about a closed system wrt thermodynamic properties.  A dissipative system is a thermodynamically open system which is operating out of, and often far from, thermodynamic equilibrium in an environment with which it exchanges energy and matter.  Also the discussion on mixtures is woefully inadequate.  Sometimes the PVT - X relationship can be taken to be linear in which case the critical properties can be estimated using KAY'S RULE, e.g. -- MCP (mixture critical pressure) = the number or molar average across the pure component critical pressures.  For example, in a 60-40 molar mixture of n-pentane and pentene-1, Pc (mixture) = 0.6*Pc (n-pentane) + 0.4*Pc (pentene-1). However, sometimes it is highly non linear requiring more homework to develop the PVT data of different X's.  This is not a good example because n-pentane and pentene-1 state properties are so close together.Danleywolfe (talk) 22:50, 18 July 2011 (UTC)

Pure substances first?
In thermodynamics, pure substances are usually considered simpler or more fundamental than 2-component systems. I suggest therefore describing the vapor-liquid critical point of pure materials before the liquid-liquid critical point of binary systems. Does anyone object to rearranging the article to place the present section 2 before section 1? Dirac66 (talk) 19:06, 8 September 2009 (UTC)

Table sorting broken
It's obvious that the table doesn't sort correctly. It's really broken. This is due to two things: First, sortable tables don't work with  or   (Bug 8028). Second, Template:Convert does not generate correct sorting keys for negative numbers or numbers with different precisions. I tried three or four different ways to work around these issues without resorting to manual sort keys, but none of them worked. Anyone? —Keenan Pepper 10:07, 1 November 2009 (UTC)


 * Why do we need a sortable table? Why not eliminate this feature and just place the rows (yes, manually) in alphabetical order? If you eliminate the sorting feature which I don't understand, I will sort the rows manually - NH3 to O2 are already sorted.
 * If there is a good reason for having a sortable table, perhaps you could explain how it is supposed to work, and give an example of another Wiki article with a sortable table which works properly. Dirac66 (talk) 11:58, 1 November 2009 (UTC)


 * OK, I have found instructions with several examples at Help:Sorting. This may help if someone reads it carefully enough. Dirac66 (talk) 16:11, 1 November 2009 (UTC)


 * Right, yes, I'm already familiar with Help:Sorting. Of course you can manually sort the table by any ONE column, but if you want the reader to be able to see the table sorted by ANY column, then you need a sortable table. A good example is List of elements by melting point. I can sort that by atomic number by clicking the first sort button, in alphabetical order by element name by clicking the second, and by melting point by clicking the last. In order to get the table in this article to work like that one, we'd have to
 * Eliminate the s and  s (which might require the table to be laid out in a less appealing way)
 * Add a manual sorting key to each numerical entry. —Keenan Pepper 18:39, 1 November 2009 (UTC)


 * Thanks for the melting point example; I see that for the reader it works like the sort function in an Excel spreadsheet. However the melting point example does not have a heading which spans 2 columns. If you want to use colspan, we need another example which does use colspan, which will permit comparison of its syntax with the syntax in this article. Perhaps we can find a difference which can be fixed.
 * If not then you just use another (perhaps less appealing) layout. Either combine the columns as in the melting point example, writing the temperatures as 647 K (374oC) etc [with K first to avoid a problem with negative numbers. Or else put each value in a separate column and use repetitive heading titles: Tc (K) in one column and Tc (oC) in the next.
 * As for rowspan, why not just suppress it as the table here never combines 2 rows anyway? Can colspan be used without rowspan? Dirac66 (talk) 19:23, 1 November 2009 (UTC)


 * You won't find any working examples of a sortable table with, for the simple reason that that combination doesn't work with the Wikimedia software yet. That's Bug 8028. —Keenan Pepper 20:36, 1 November 2009 (UTC)


 * OK, then as long as Bug 8028 is not fixed, we will have to choose between the sorting functionality and the most appealing layout. I assume you prefer sorting functionality, so I suggest starting by following the melting point model as closely as possible in order to get one version that works. After that you can try making layout changes (without the colspan feature) and see if they still work. Buena suerte. Dirac66 (talk) 21:48, 1 November 2009 (UTC)

Surprise! Today Wikid77 has found a fix to make a sortable table without colspan, but with the headings arranged the same way. Thank you for solving the problem. Dirac66 (talk) 13:46, 2 November 2009 (UTC)


 * The headings don't line up at all for me. See Image:Critical-point-table-screenshot.png. I think this is because it uses units of "px", but my screen is pretty high resolution so the text cannot fit in a table of that many pixels. Even if we used a resolution-aware unit like "em", I don't think this is a good solution because two independent tables are never guaranteed to line up perfectly. It's an ugly hack. —Keenan Pepper 16:04, 2 November 2009 (UTC)

What material has the highest critical temperature
Would it be graphite? What would be the temperature, approx? [Question by 142.103.44.67 dated 5 April 2011]
 * First I have this moved this new section to the end of the talk page.
 * Graphite is a solid form of carbon, whose liquid-vapor critical point is estimated at 6810 K (HR Leider et al, Carbon, 11, 555-563 (1973). This is lower than the values in the article for Fe, Al and Au. So for now the highest value in Wikipedia is Fe at 8500 K. Does anyone know a higher one?
 * I think also that all these values are only theoretical estimates, since at such high temperatures there is no container that will hold a liquid. Dirac66 (talk) 14:04, 6 April 2011 (UTC)

History
"The existence of a critical point was first discovered by Thomas Andrews in 1869 for carbon dioxide." This sentence may need modification. The discovery of the critical point for carbon dioxide may be first discovered in 1869 but the existence of the critical point was discovered by Charles Cagniard de la Tour in 1822. (http://en.wikipedia.org/wiki/Charles_Cagniard_de_la_Tour) --Mirrordor 17:58, 28 September 2011 (UTC) — Preceding unsigned comment added by Mirrordor (talk • contribs)


 * Apparently Cagniard de la Tour made the first known observation, and Andrews went much further. So we have to sort out what each actually contributed. A possible starting point is this paper Critical phenomena: 150 years since Cagniard de la Tour by Berche et al. (2009) Dirac66 (talk) 18:20, 28 September 2011 (UTC)

Critical Point reflects strength of inter-molecular forces ?
Above the critical temperature, gas & liquid phases are indistinguishable. Below the critical temperature, gas phases "condense" into liquid phases, when free flying gas particles "coagulate" due to inter-molecular forces. Logically, if the particles had energy in excess of the same, then those inter-molecular forces would become energetically moot. Perhaps the critical temperature reflects the strength of inter-molecular forces (E ≈ kBTc) ? 66.235.38.214 (talk) 03:16, 15 October 2012 (UTC)
 * I think it is accepted that there is a correlation between critical point and the strength of intermolecular forces. When the liquid is heated above the critical point, the molecules have too much kinetic energy to be confined by the forces, although they still influence the molecular motion so that the gas is not ideal. Dirac66 (talk) 13:42, 15 October 2012 (UTC)

Liquid-solid critical point?
If there is a critical point, above which gas & liquid are effectively indistinguishable; then perhaps there is another critical point, above which liquid & solid are indistinguishable? Cp. material in earth's mantle, which is said to be solid, yet which flows under load. Perhaps, too, plasmas plot far to the right, above-and-beyond all critical points, so that plasmas compress continuously, from gas-like (low P) through liquid-like to sold-like (high-P)? Ultimately, at super-high pressures, perhaps materials compress into "neutronium", as speculated to exist inside of neutron-stars? Cp. the following figure:
 * http://s17.postimage.org/ecdbmzq3j/All_Phases_diagram.png
 * 66.235.38.214 (talk) 04:13, 15 October 2012 (UTC)
 * This suggestion is speculative. Although many have wondered if there might be a liquid-solid critical point, I am unaware of any actual evidence for one. Dirac66 (talk) 13:42, 15 October 2012 (UTC)

Vapor / Gas differentiation
What is the assumed difference between vapor and gas in this article? — Preceding unsigned comment added by 72.131.51.226 (talk) 13:29, 25 June 2016 (UTC)


 * Good question. The answer is explained in the vapor article, but not in this article (yet).
 * A vapor is a gas at a temperature below the critical temperature. This means that a vapor can be liquefied by increasing the pressure without cooling. At temperatures above the critical point, the word gas must be used and the gas can only be liquefied by cooling. Dirac66 (talk) 21:29, 25 June 2016 (UTC)

In renormalization group theory seems out of place
This section In renormalization group theory should perhaps move to that article - does not seem relevant here. This is not a disambiguation page. - Rod57 (talk) 12:53, 29 April 2017 (UTC)


 * The section is in fact about one theory which describes critical points and critical phenomena at a more advanced level, so I have moved it to the more advanced article Critical phenomena, which seems a more appropriate place for it. Dirac66 (talk) 01:56, 2 May 2017 (UTC)

Some other physical examples would be useful
A brief mention and links to some other critical phenomena would be very helpful, if they exist: I suspect that the Curie point could go here, maybe Néel point... perhaps there are others. Latrissium (talk) 20:48, 17 November 2017 (UTC)

Newton's correction?
This subject was added a few days ago by VipulRamtekkar. More details and a reference are clearly needed. A Google search found this article by Maslan and Littman. It appears from the first page that this is an empirical correction used in the calculation of thermodynamic properties such as activity coefficient and compressibility, although I don't have access to the complete paper. I don't really think it is relevant to this article on critical point; perhaps it would be more relevant to the articles on activity coefficient or compressibility.

Also Newton should be identified by adding initials (in the complete paper?). Certainly it was not Isaac Newton who died in 1727, as critical points were discovered in 1822 and activity coefficients defined about 1900! Dirac66 (talk) 01:09, 13 March 2018 (UTC)


 * Perhaps the mention of "Newton's correction" is intended to be a correction based on a derivative, similar to Newton's method:
 * $$f(x_1) = f(x_0) + correction$$
 * $$f(x_1) \approx f(x_0) + (x_1 - x_0)f'(x_0)$$


 * Dolphin ( t ) 01:29, 13 March 2018 (UTC)

Reduced Volume Error
The expression given for reduced volume looks incorrect. Typically one states the critical molar specific volume

$$ V_{m,c}=3b=\frac{3}{8}\frac{RT_c}{p_c} $$

as in the article on the Van der Waals Equation. The reduced volume $$ V_r $$ is then given in terms of the molar specific volume $$ V_m $$ and the critical molar specific volume $$ V_{m,c} $$ as

$$ V_r = \frac{V_m}{V_{m,c}} = \frac{V_m}{\frac{3}{8}\frac{RT_c}{p_c}}. $$ Eshort0401 (talk) 08:57, 6 December 2022 (UTC)


 * This formula would need a source to be taken seriously, according to the rules of Wikipedia. Dirac66 (talk) 02:36, 18 March 2023 (UTC)

"Critical point (physics" listed at Redirects for discussion
The redirect [//en.wikipedia.org/w/index.php?title=Critical_point_(physics&redirect=no Critical point (physics] has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at  until a consensus is reached. Utopes (talk / cont) 01:12, 20 January 2024 (UTC)