Talk:Phase (matter)

Title is misleading

Here and in the 'list of Phases of matter' article there is confusion between the usage of 'phase' to denote the difference of liquid vs. solid as opposed to the the difference between diamond and graphite. The liquid vs. solid distinction is properly a difference in 'state of matter' -- yes they are necessarily different phases, too. However, in the diamond vs. graphite case, both ate the same state of matter (solid) but different phases.

There is much in the first two paragraphs which do not belong in an article on phases, but which should instead be part of an article on 'states of matter'. Although there may be some contexts where 'phase' and 'state of matter' may be used interchangeably, it only adds to the confusion here.

I propose that the solid/liquid/gas/Bose-Einstein condensate part of this article be removed to another article dealing with states of matter, and this article focus on the other meaning (diamond vs. graphite, fcc-iron vs. bcc-iron, liquid miscibility issues like oil/water, etc.) Olof

Confusion, or a difference in terminology? I understand "states of matter" to be a lay term referring to the three principal STP phases (solid, liquid, gas). I agree that there could be improvement, but splitting up the article is unlikely to help. Also, allotropy has its own article already. Do you have a citation for your usage of the terms? –EdC 13:49, 10 January 2007 (UTC)

For example, the discussion in Gibbs' phase rule uses the sense of 'phase' I propose above, and is in contradiction to the use of 'state'. Same for phase diagram - the use of 'phase' there matches my definition.

By contrast, the P.W. Atkins textbook 'Physical Chemistry' (third edition, 1986) includes this quote on page 10: "Casual inspection of the familiar world reveals the existence of three states of matter: solids, liquids and gases. Closer inspection shows that some materials existin different crystal forms (e.g. carbon can exist as diamond or graphite). These varieties of matter are called its 'phases' ... in rare instances, even the liquid state of a material may occur in different phases with sharply distinct properties" -Olof

OK, but how are you going to explain phases without reference to the most obvious phase boundaries? Also, what could be the content of an article on "state of matter"? To provide explanations of the solid, liquid and gas phases it would have to repeatedly refer back to this article, or duplicate lots of material. I don't see we need anything more than a paragraph at most explaining when and why the solid/liquid/gas phases are referred to as states, and what the relevant physical quantities are (and possibly how they change at phase boundaries). –EdC 04:41, 11 January 2007 (UTC)

I disagree completely. An article on states of matter need not make excess reference to the concept of phase. Making the point that the different states of matter (solid, liquid, gas) can be differentiated based on physical properties seems pretty easy. Indeed, an article about the states of matter had better be concerned with those differences. If anything, such an article would make excessive reference to the articles on gas, liquid and solid. And it would make sense for those articles to point to an article on states of matter, not phases.

On the other hand, an article about phases can provide examples where phases can be differentiated even though the state of matter is the same (oil and water, diamond and graphite, austenite and ferrite, the various iron oxides, the two phases of liquid He, order-disorder transitions, the superconducting transition, spinodal decomposition, crystallization in glasses, phases in 2D surface reconstructions and on and on. And it makes sense for the articles on the phase rule and phase diagrams to point to an article on phases rather than an article on states of matter. The phase rule does not apply to the number of states in a system, it applies to the number of phases. -- Olof

Yes, but what are those differences? This is physics, not taxonomy. –EdC 13:43, 11 January 2007 (UTC)

State of matter disambiguated

So I've gone and done the disambiguation between state of matter and phase. I believe a number of other articles now are more coherent, and a number of links make more sense.. However, there are plenty of loose ends to do -- and I'm not really sure what to do with the states of matter template -- Olof (talk • contribs) 10:01, 11 January 2007 (UTC).

OK, I'm not too unhappy with what you've done. However, there are some obvious problems:

• "Phases are sometimes confused with states of matter, but there are significant differences. States of matter refers to the differences between gases, liquids and solids, etc."

This is a content-free sentence. The article needs to explain why and how phases are clustered into states.

Other issues, but that's all for now. –EdC 13:42, 11 January 2007 (UTC)

I have a problem with this distinction as well. I am not sure it exists in any field of science, it is not tied to any definitions, in it is not articulately stated. —Preceding unsigned comment added by Pvkeller (talk • contribs) 22:00, 8 November 2008 (UTC)

Some careful rewriting is certainly necessary, but note that there is a real distinction between a 2-phase system and a 2-state system. For example an oil-water system has 2 phases (for certain compositions) but only one (liquid) state. Dirac66 (talk) 01:42, 9 November 2008 (UTC)

I think the definitions as they presently appear are wrong. A phase is a region of a system throughout which all properties are uniform. (Ref. Modell & Reid, Thermodynamics and its Applications (1974) - Maybe not the latest, but an esteemed classic.) But naming the phase and identifying its type does not tell you all the properties of matter in that phase (specific heat, density, etc.). For that, you need to specify temperature, pressure, composition, and anything else that is independently required to reproduce whatever state of matter you are taking about. See thermodynamic state. That's why you need to define "state of matter", which is something more and quite different from simply "phase". I do not see any reference on either page that points towards a different usage of the term "state of matter" from the one I propose. If I change the pages to match these definitions, is anyone going to protest?Paul V. Keller (talk) 02:27, 13 November 2008 (UTC)

Reading some of the talk, it occured to me that the original intent may have been to use the "state of matter" page to talk about organizations of matter in systems that can be multi-phase. For example, perhaps there was some desire to talk about emulsions versus separated liquid phases or suspensions versus solutions. But I do not see any use for such a definition for "state of matter". What would be the gain in talking about suspensions, colloids, and water-ice systems all on the same page? On the other hand, I can see separate pages for phase behavior (the ways in which matter in equilibrium organizes into one or more phases), phase distribution (possibly a subset of the last, but optionally focusing more on how matter distributes in multi-phase systems, interfacial phenomena, emulsions, colloids, suspensions, liquid crystals, saturation, and solutions. (some of these present already, and some not).

The long and short of it is I cannot think of a situation in which someone would come across the term "state of matter" and want to read about oil-water two-phase systems and solid suspensions on one page. On the other hand, any information about various kinds of phases fits better in the "phase" pagePaul V. Keller (talk) 16:27, 13 November 2008 (UTC)

Question

Hi there. I was reading this article, and found myself amazed with those two sentences which seem contradictory to me :

• "a phase is a set of states"
• "If there are two regions in a chemical system that are in different states of matter, then they must be different phases"

So my question is : How can we have a phase as as set of states when two states have necessarily two different phases ?

Does the first sentence may in fact be "a state is a set of phases" (which is not as correct as "a system can have multiple phases which are in equilibrium with each other and also in the same state of matter" -I think the best "all-in-one" of this article)

Am I missing something or is my comment right ? --JcDenaes

The issue is the overloading of the word 'state'. 'State of matter' as a set phrase usually refers to that property of a substance which is one of liquid state, solid state, gaseous state, and a few exotic possibilities (plasma, etc.). When we say 'two states have necessarily two different phases', that means if one thing is a liquid and another thing is a solid, they must be different phases.

You are right to pick on the phrase "a phase is a set of states" as being confusing. It is. Here's an example where you might use it: Some metals go through a phase transition to and from superconductivity at low temperatures -- a transition to the superconducting state. That's a different kind of state from 'state of matter', because such a metal will still be a solid, but in this case, the distinction of superconductor vs. conductor is one of the set of states that distinguish a phase. 'State of matter' is one, 'state of conductivity' is another.

--Olof

Thank you a lot ! I understand now. --JcDenaes

Second order phase transitions

There are several misconceptions of phases, and specifically phase transitions in this article. Mostly, it completely ignores second-order phase transitions, in which the free energy function stays differentiable, even at the transition. This also means, that the latent heat (energy related to the change in phase) is zero at the critical value. A perfect example of this is mentioned just above here: the superconducting phase transition. At some critical temperature (or critical magnetic field strength, but this is a bit touchy, as some energy is related to displacing the magnetic field around the superconductor), metallic superconductors become superconducting, which, as mentioned, is a different phase of matter. However, no energy is released in the process, nor is any taken up. This is in clear contradiction to a number of statements in the "General definition..." section. The page on phase transitions has a much clearer description, which should be linked to in stead. 195.215.65.50 (talk) 21:59, 28 November 2007 (UTC)

Fall 2008 re-write

Further to a discussion above, I undertook a significant rewrite.

The definition of a phase as a "set of states" is now gone. The definition seems to be based on looking at phase diagrams and is not commensurate with the definition in my references, which I know is widely used. The "set of states" definition works poorly when you watch what happens to liquid and gas phases around and "above" the critical point.

I also took out the definition of phase boundaries in terms of the free-energy becoming "non-analytic" That definition seems to derive from experiments where you observe sudden changes in things such as heat capacity as your system moves from a single phase into a two phase region (or back the other way). This type of behavior gets treated in a different guise by the new version. Non-analytic seems to be meant with reference to the phase diagram (derivatives with respect to pressure and temperature), not with respect to space (derivatives with respect to spatial coordinates). Again, the definition based on phase diagrams and phase experiments is certainly not universal. I also wonder whether it is practical outside the study of phase diagrams.

Another problem with the old description and definition is that it was of little or no practical use to anyone who might consult this page. I know I did not understand it the first few time I read it in spite of my have background in this area.

At the risk of belaboring the point, it occurred to me that a phase diagram-based definition of phases breaks down in the face of super-saturation and bubble nucleation. In both cases, you have a phase that exists outside its bounded domain on the phase diagram. Until you get that first crystal, or that first bubble of adequate size, the expected phase transition does not occur. —Preceding unsigned comment added by Pvkeller (talk • contribs) 20:53, 25 November 2008 (UTC)

The description under "phase separation" also received the axe. The removed material referred to a mathematical model of fluid movement in a dynamic process of phase separation. It was not a model describing when phase separations would occur. It was distracting, meaningless, and useless to nearly anyone who might consult this page. Also, the content was only remotely related to the main topic.

I removed material about solubility, which is a different topic.

If you are looking for a description of the exemplary system having eight immiscible liquid phases, check the footnotes. My reason for removing most of that description was that it did not add enough to the discussion to deserve the space it was taking.Paul V. Keller (talk) 17:17, 25 November 2008 (UTC)

I agree that the rewritten article is at a better level for most readers including chemistry students, and that much of the deleted material was overly mathematical for this article.

I think the next step is to add references to appropriate sections of some standard physical chemistry books, for example Atkins and de Paula. Dirac66 (talk) 23:12, 25 November 2008 (UTC)

Adding references would be great, but I realized there is still work to be done on the content. Is the other, distinct definition of a phase as a "set of states" in use? Is water said to have X distinct solid phases or X distinct crystal states? If the transition from ordinary medal to superconducting metal involves a phase transition, is the superconducting state described as a distinct phase or a distinct state? I would need to research this. I think we will need to revise this page to reference the second definition or modify the state of matter page. I do not like to leave this unresolved, but do not have time to look further into it at the moment.Paul V. Keller (talk) 14:27, 28 November 2008 (UTC)

First, I realized that the reference which you did add (Modell and Reid) did not appear in the article because your rewrite accidentally omitted the ==References== section with the source code which makes references appear. I have now fixed this.

As for distinct phases vs. distinct states: The enumeration of phases is clear because a phase is well defined as a region with uniform properties. So ice I and ice III are two distinct phases because their density is different, as are normal aluminum and superconducting aluminum because their conductivity is different (one finite, one infinite). Counting phases this way is necessary to satisfy the phase rule: ice I and ice III are in equilibrium on a curve (1 degree of freedom) just like ice I and water, so F=C-P+2 requires that P=2.

The word "states" has several different meanings, as we have already discussed at Talk: State of matter#States of matter vs. Thermodynamic state. The "set of states" definition refers to "thermodynamic states", e.g. ice I at -10^oC and 1 atm, ice I at -9.9^oC and 1 atm, etc. These refer to one and the same phase whose properties vary slowly. If you want to put this definition back in the article, then "thermodynamic states" would be much clearer.

As for different "crystal states" such as ice I and ice III, their enumeration is variable depending on the author and often the context for the same author. Sometimes "state (of matter)" is used as a synonym for "phase", and other times phrases such as "solid state" imply that ice I and ice III are in the same state. Similarly for normal and superconducting phases of a metal. This is a confusing and unfortunate situation, but Wikipedia cannot impose precision upon the scientific world. Best I think to use "phase" (and perhaps "thermodynamic state") in this article, and keep "states of matter" in the other article without a precise enumeration. Dirac66 (talk) 03:32, 30 November 2008 (UTC)

I think the only correct answer is to report actual usages. What I found is that various researches variously if not interchangeably use different terms to describe waters various crystal types, the terms including crystalline phases, ices types, and ice states. I personally prefer describing them as different states of matter, with the understanding that the states are differentiated in terms of organization of matter. My preferences, however, are not relevant. I think our job is to report on actual usage, although we are free to organize and explain.

To clarify, neither phase nor thermodynamic state adequately describes regions of the phase diagram. Phase includes non-equilibrium and unstable conditions. For example, super-heated water is a phase of the liquid type. Under the "set of states" definition, it would be identified as part of the gas phase. Thermodynamic states refer to discrete conditions, not ranges of conditions. I propose to add a section to the state of matter page and a cross-reference on the phase page, pointing out how the terms are actually used on both pages.

Btw, I read the transition to a superconducting state does involve the crossing of a phase boundary.Paul V. Keller (talk) 20:51, 30 November 2008 (UTC)

I removed material about solubility, which is a different topic. If you are looking for a description of the exemplary system having eight immiscible liquid phases, check the footnotes. My reason for removing most of that description was that it did not add enough to the discussion to deserve the space it was taking. Solubility isn't really a "different topic". Wikipedia isn't a physics textbook, but rather a general reference. When people search for "phases", this is hopefully the first relevant page they'll find. It must be mentioned on this page that certain substances separate into phases, which are mixtures of the compounds. This phenomenon is not off-topic. Also, what kind of phases can form is also helpful. The short summary doesn't have to deleted because there is a general article Solubility, which, at the current state, actually discusses the issue in a rather cursory manner. Furthermore, there are instances where solubility, or the simple description of it, does not correspond to spontaneous phase separation. Aside from these specifics, removing the link to solubility and the advice "check the footnotes" is not acceptable. To answer to the question of the space it takes, it is a technical/copyediting question. --Vuo (talk) 12:45, 1 December 2008 (UTC)

I'll grant you I took out more than was necessary and that it was not accurate to say solubility is an entirely seperate topic. However, I object to the way you left the content: it introduce solubility without tying the term to the main topic. The discussion of the Hidebrand solubility parameter is out of place, and to say immiscibility shows mutual insolubilty overlooks that there is often a certain amount of component A in the B-rich phase and vice versa. I am making changes accordingly.Paul V. Keller (talk) 20:47, 1 December 2008 (UTC)

IUPAC Gold Book

(continues previous section: Fall 2008 re-write)

In chemistry the recognized authority for definition of terms is IUPAC, at least for the limited number of terms they consider. The IUPAC Gold Book defines "Phase" as "An entity of a material system which is uniform in chemical composition and physical state." [1] This is similar to what we have now, and I think we should use the words of IUPAC as the initial definition to start the article, with a link to the Gold Book.

IUPAC does not refer to a set of states, but we could add a remark after the definition. Perhaps something like "For systems in equilibrium, a phase may be considered as a set (or range) of thermodynamic states whose properties vary continuously." Yes, I did forget about non-equilibrium states until reading your last edit; if we follow IUPAC and do not present this remark as a general definition, then we can just exclude them with the initial phrase "For systems in equilibrium".

Unfortunately the Gold Book does not help with state of matter, which is not among the 6852 terms it defines. Dirac66 (talk) 01:30, 1 December 2008 (UTC)

It has to be clear that we are not merely putting the definition in a different way, but talking about an overloaded word.

Gold standard or not, the Modell & Reid definition is more precise, although I agree the difference is small. The authors were MIT professors researching and teaching thermodynamics. I have no idea who writes the IUPAC. I trust my authors thought about the words of their definition very carefully and were informed by many issues that arise in the field. It seems to me "entity" could be ambiguous if not confusing, as could the meaning of "material system". We have useful definitions of system and thermodynamic state and it makes sense to leverage those in the absence of equivalent options.Paul V. Keller (talk) 01:58, 1 December 2008 (UTC)

Well, the Modell-Reid definition is certainly clearer, and close enough to the official IUPAC version so that I think it is acceptable. I agree that "entity" is certainly a confusing word, and "region" is much clearer. The important point is that the basic definition should contain the idea of a uniform subsystem (entity or region in physical space), rather than the idea of a set of states (in parameter space) which is more complicated and also only applies to equilibrium systems. Dirac66 (talk) 04:09, 1 December 2008 (UTC)

500+ phases

According to [2] doi:10.1126/science.1227224 there should be more than 500+ phases -- 70.24.247.127 (talk) 01:27, 25 December 2012 (UTC)

Yes, there are more than 500+ phases. In fact, the Inorganic Crystal Structure Database has 161,030 entries, each of which represent a phase (although some might not have a phase boundary between them). As the authors of the Science paper state in their abstratc, by symmetry arguments alone, there are 230 possible different crystal structures, each of which would need to be its own phase. More phases are indeed possible when one considers additional degrees of freedom. Are you asking us to clarify the number of topologically distinct phases possible in general? Mgibby5 (talk) 14:44, 5 February 2015 (UTC)

List of phases?

I would like to have all known phases of matter listed somewhere, either in the form of a bullet list or as a table. Currently, you just have to read the text in hope of finding them all implicitly listed somewhere, although they are not. Could anyone who know which all these phases are please make a list of them? —Kri (talk) 21:03, 21 July 2014 (UTC)

It is fairly inconvenient to list all possible, distinct phases: each different crystal structure is a different phase, by symmetry arguments. Further, several different phases can exist in equilibrium with each other, but each have the same crystal structure, just as liquids can exist in equilibrium with one another (oil and water are separate phases, despite possessing the same symmetries). It is not useful in practice to provide a list of all possible phases. Mgibby5 (talk) 14:37, 5 February 2015 (UTC)

History

Can we have a section on the history of the discovery of phase structures, please? — Preceding unsigned comment added by 176.252.227.106 (talk) 13:08, 25 January 2015 (UTC)

Right amount of water

In the last paragraph under number of phases is the following: "By charging the right amount of water and applying heat, the system can be brought to any point in the gas region of the phase diagram. "

1) The syntax of charging the right amount of water seems a bit clunky and probably refers to a specific experimental apparatus? I interpret it to mean controlling the amount (mols I assume - but that is problematic because we don't have a vloume) of water in the described system.

2) Going from the amounts issue above: the relative amounts of material in a system is a variable that can affect phase but is not what is represented in the attendant 2D phase diagrams (only T & P are). It is probably best to avoid adding compositional axes too for this discussion.

Suggestion: Could we edit this to say something like "By controlling the temperature (degrees K) and the magnitude of pressure (here shown in MPa) the system can be brought to any point on the phase diagram. From a point in the solid stability region (left side of diagram) increasing the temperature of the system would bring it into the region where a liquid or a gas is the equilibrium phase (depending on the pressure).

By CrispGeochem — Preceding unsigned comment added by 151.213.119.209 (talk) 16:27, 1 May 2020 (UTC)

Good suggestion. I have copied most of your two sentences into the text, although I left out the units since other units could be chosen also. Dirac66 (talk) 15:32, 9 May 2020 (UTC)