Talk:Triple point

message: The article correctly says of water,
*"At that point, it is possible to change all of the substance to ice, water, or steam by making infinitesimally small changes in pressure and temperature."
That may be technically correct, but I find it misleading. At the triple point, it is very hard to make an infinitesimal change to the pressure or the temperature. An infinitesimal addition or removal of either volume or heat will only change the concentrations of the phases, while the pressure and temperature stably remain at the triple point. Only when one or the phases is exhausted can you move away from it. This stability is what makes the triple point useful as a standard, and it is the reason why saying "at the triple point" is meaningful at all. To speak of destroying the balance between the phases with an infinitesimal change completely misses the point (har!) and borders on wrongness.
Now, I'm not confident enough in my chemistry to change the article, but someone ought to. Melchoir 11:43, 25 February 2006 (UTC)
thread_title:  Infinitesimal changes? 

message: Although a triple point can generally mean any intersection of boundaries, the thermochemistry meaning is the most common. I think the geography concept should split to a new article; Triple point (geography) would be fine, but Triple divide is less ambiguous. Melchoir 23:02, 31 March 2006 (UTC)
replies: text: Very well, suit yourself! Melchoir 03:06, 1 April 2006 (UTC)
thread_title:  Split Geography to [[Triple divide]] 

message: Correction: Triple point can also mean not only where solid, liquid and gaseous phase meet, but also where any phases meet (such as triple point of ice III, ice II and ice V).
:Feel free to correct the article! If you can provide a reference for the definition, that would be perfect. Melchoir 20:27, 5 May 2006 (UTC)
replies: text: Two points define a tine. The temperature scale is constructed so that Absolute Zero corresponds to exactly 0 K, and the triple point corresponds to exactly 273.16 K. —68.239.176.150 18:43, 13 March 2007 (UTC)
replies: text: This actually has the effect of making the freezing point of water not equal to precisely 273.15 K or 0° C at standard pressure, nor is the boiling point of water 373.15 K at standard pressure. Simply put, the definition points of both scales were moved to absolute 0. and the triple point of water, generating exact temperatures for those quantities. 68.239.176.150 18:51, 13 March 2007 (UTC)
thread_title: Definition of triple point

message: Currently there is this remark in the text:
:(Note that the pressure referred to here is the vapor pressure of the substance, not the total pressure of the entire system.)
For the triple point to be well-defined, it seems clear that the gas phase should be the pure vapor of the substance, and not, for instance, its vapor mixed with air. Otherwise, the two other phases would "feel" the total pressure, instead of only the vapor pressure, and their thermodynamical characteristics would be slighly offset from what they are at the real triple point.
If I am correct about that, I think it should be specified in the text (by someone who writes better than I do :-D).
The remark quoted above should also be removed, or reformulated.
David Olivier 23:16, 26 May 2006 (UTC)
replies: text: Since nobody said nothing, I'm going to change it!89.137.187.188 (talk) 08:55, 24 March 2008 (UTC)
thread_title: Vapor pressure or pure vapor?

message: Pure water is a mix of isotopes: the hydrogen atoms can be deuterium, or even tritium. There are also different isotopes of oxygen. Presumably, the precise temperature of the triple point depends on the isotopic composition of the water. And presumably, that isotopic composition depends on the kind of water; rain water, for instance, results from evaporation of sea water, and might be poorer in heavier isotopes than sea water.
So: did the definition of the kelvin as 1/273.16th of the triple point temperature specify the isotopic composition of the water?
David Olivier 23:29, 26 May 2006 (UTC)
thread_title: What isotopes?

message: In the opening phrase: it is not gas, liquid and solid that coexist at the triple point.
It is quite more accurate to write vapour, liquid and solid.
It should be also stressed that the triple point is certainly a point in a p-T chart ---shown in article---
but it is a line in other charts (T-V or p-V). Unlike critical point that is one
and just one equilibrium state ---a point in whichever chart---.
Etaoin Shdrlu 11:55, 7 October 2006 (UTC)
replies: text: Those who don't understand might usefully read about steam and water vapour. --David Biddulph (talk) 18:00, 8 December 2014 (UTC)
thread_title:  vapour 

message: I put back the sentence that had been deleted on 16 November by 69.109.172.9:
:Strictly speaking, the surfaces separating the different phases should also be perfectly flat, to avoid the effects of surface tensions.
The comment on the deletion was that the sentence is offtopic. I think 69.109.172.9 misunderstood the sentence, because it clearly is not offtopic. Perhaps it could be better formulated. But it does have some importance, because an equilibrium between water vapor, ice and liquid water in the form of very small droplets would not be at the triple point! David Olivier 18:56, 17 November 2006 (UTC)
thread_title:  Flat surface 

message: Non-contributing user dropping in to point out that the link in the phase diagram's caption regarding water's unusual freezing point is dead, as the water article has since been edited. 134.226.1.234 15:38, 13 February 2007 (UTC)
thread_title:  Dead Link 

message: How do impurities affect the triple point of water - can anyone provide a good ref? sbandrews (t) 19:18, 16 March 2007 (UTC)
thread_title: Impurities

message: can someone either improve that section or delete it? it seems rather without anything useful to me. maybe move it to the article on Mars? 66.215.211.119 16:33, 24 August 2007 (UTC)
thread_title:  That random bit about Mars 

message: A leading benefit engineering firm based in Indianapolis, Indiana  —Preceding unsigned comment added by 65.29.79.242 (talk) 05:12, 6 September 2007 (UTC)
thread_title:  Triple Point Consulting 

message: I've removed the random Mars fact. It's un-sourced and talks about the pressure of a triple point. Robertcornell68 (talk) 14:50, 7 December 2007 (UTC)
thread_title:  edit: Mars 

message: I've changed the opening sentence from "in physics and chemistry" to "in thermodynamics". This is more precise, and indeed if we are listing subjects like chemistry and physics, why not also add engineering and biology, which also make use of the triple point. Thermodynamics is a sub-branch of all these subject and the correct term to use.  —Preceding unsigned comment added by 84.71.165.54 (talk) 18:00, 23 July 2008 (UTC)
thread_title:  edit: Opening sentence 

message: The reason for supposing p\choose 3 triple points for p phases is obvious, but I don't think it takes into account the possibility of isolated phases that do not touch every other phase.  (For example, 5 phases would only have four triple points if one of them was a square and the others lay between nonintersecting rays emanating from its corners.  3 phases that were independent of one variable would have no triple points at all.)  Are such phases prohibited (or vanishingly rare), or does there need to be an "up to" in that sentence?  --Tardis (talk) 22:15, 19 May 2009 (UTC)
replies: text: That's a good point, I think "p choose 3" is an upper limit. The water phase diagram has plenty of phases that don't touch every other phase. --Itub (talk) 13:02, 20 May 2009 (UTC)
replies: text: I think that for p > 4 it's impossible to have p\choose 3 phases triple points, and the maximum is much less than this for large p.  For starters, the four color theorem means that the phases can be divided into four sets such that no two from the same set can be part of a triple point (they can be part of a quadruple point, etc., but I don't think that's important).  For p = 5, this puts an upper limit of 7 on the number of triple points.  It gets worse as p gets larger. 72.75.86.126 (talk) 13:31, 15 August 2009 (UTC)
replies: text: I see it's a little more complicated after looking at the reference.  There's a subtle point of definition that's important.  If all that's required is thermodynamic equilibrium (equal chemical potential) of three phases, they can have a triple point in the region of a fourth phase, which will be unstable with respect to that fourth phase.  In the example above with the square and rays, for example, some of the triple points may be within the square.  But the definition given here says that the phases coexist.  I think this will confuse people, even if it is in a sense correct. 72.75.86.126 (talk) 14:10, 16 August 2009 (UTC)
thread_title:  p choose 3: really? 

message: I'm confused about the following passage...
At high temperatures, increasing pressure results first in liquid and then solid water. (Above around 109 Pa a crystalline form of ice forms that is denser than liquid water.)
This does not jive with the graphic accompanying.  According to the diagram, increasing pressure at a given temp above the tp-temp would not ever cause water to change from liquid to solid, due to the anomalous nature of water.  However, the sentence above clearly reference *water*.
Does the dotted green line head over left at higher pressures (i.e. above 109 Pa?)  should the sentence in question reference another substance? - Dmc lat47 (talk) 13:08, 13 January 2010 (UTC)
replies: text: This should be 109 Pa or 1 GPa. This high pressure region is not shown on the diagram now in this article. A phase diagram showing the high-pressure forms of ice is at Ice#Phases. Dirac66 (talk) 20:47, 30 June 2011 (UTC)
thread_title:  Phase diagram indicates that water should never turn to solid above the tp temp 

message: The slope of the solid-liquid line above the triple point looks wrong. It is portrayed as unchanged from the slope below the TP, except for water. Actually, the slope will generally become very large, whether it remains positive or (as for water) turns negative, since the liquid-solid volume change is typically small.Unfortunately I don't know how to edit the graphics.  — Preceding unsigned comment added by Mbweissman (talk • contribs) 23:33, 3 January 2012 (UTC)
thread_title:  slopes near triple point 

message: I note that the lead section says (emphasis added) "The triple points of several substances are used to define points in the ITS-90 international temperature scale, ranging from the triple point of hydrogen (13.8033 K) to [...]", but §3, "Table of triple points", gives the temperature of the triple point of hydrogen as . I have little education in physics or chemistry, so I don't want to try to resolve this inconsistency myself, but I'm pointing it out in the hope that someone better-versed in the subject can investigate the matter. I looked up the source for the value of , the 2004 edition of the textbook Fundamentals of Thermal-Fluid Sciences, on Google Books, and found that, while Google has a limited preview only for the 2016 edition and a snippet view only for the 2008 edition, the latter shows part of a table that looks like the one in §3, including the value "13.84", whereas the 2016 edition does not mention "13.84" (to Google's knowledge) and refers to  as the triple point of hydrogen. I note that both aforementioned references to  as the triple point of hydrogen are in the context of ITS-90; is it possible for the triple point of hydrogen to differ in other contexts?  — 8573dde5 (talk) 22:09, 26 September 2018 (UTC)
thread_title:  Inconsistency in the temperature of the triple point of hydrogen 

message: Table of triple points not sorting by pressure (at least in my chrome browser). - Rod57 (talk) 18:18, 24 March 2022 (UTC)
replies: text: The sorting works in my Firefox browser. Dirac66 (talk) 19:00, 24 March 2022 (UTC)
thread_title:  Table of triple points not sorting by pressure