Talk:Chemical equilibrium

Article replaced

After extensive consultation (see below and also my talk page) I have completely replaced the text of this article. The original article was fundamentally unsound in its treatment of the thermodynamic aspects and the issue of chemical activities. Also, the kinetics approach (law of mass action) to defining the equilibrium concept, while historically important, is not universally valid as explained in the lead-in. However, I have tried to retain the good features of the original article, albeit in modified form. In addition, the points made below regarding ICE and ionic strength have been answered in the revised article

The revision is in effect a merging of chemical equilibrium (this article) with equilibrium constant, though at the same time as replacing this article I am also replacing the contents of equilibrium constant. There is also a new article on the determination of equilibrium constants which deals with experimental aspects.

The three articles, taken together, comprise a significant expansion of the originals, I believe this is a major improvement; if it were not so, I would not have done it.

Petergans 17:26, 16 May 2007 (UTC)[reply]

Comments

I've moved the recent comments here so as not to confuse them with comments on the original article Petergans 20:33, 16 May 2007 (UTC)[reply]

I am strongly opposing the complete replacement of the articles chemical equilibrium and equilibrium constant. It is highly unusual and disrespectful to previous editors. Also the concerns I have raised earlier (see above) have not been dealt with and valid content has been erased. Propose reversal on both. V8rik 19:46, 16 May 2007 (UTC)[reply]

- I don't disagree with it in principle. It may be unusual, but that's because few people invest the considerable time necessary for a complete rewrite. As long as the end result is better, I don't care. The only question that matter is, is it better? In my opinion it is better overall. However, the specific issues should certainly be discussed. Of course, anyone can still edit the article. --Itub 20:11, 16 May 2007 (UTC)[reply]

- - B8rik's concerns are not invalid. This rewrite had done away with a lot of the good features of the previous article including, unbelievably, an entire section of content. I've re-added all that and made many more improvements. I hope the current version is better than both the original and the rewrite. I will be giving the same treatment to equilibrium constant. Loom91 09:43, 17 May 2007 (UTC)[reply]

Loom91, your actions are irresponsible. Please revert back to my original. I don't want to start a reversion war, but I will if I have to.

By all means let's have a discussion about improving the article and then act by agreement. You should also respect the fact that, in this field, I am an expert with more than 30 years experience of research and teaching at Leeds University. I have published similar articles, which were peer-reviewed, in Encycopedia of Supramolecular Chemistry. What are your qualifications? Petergans 10:31, 17 May 2007 (UTC)[reply]

Despite the fact that I agreed that your complete rewrite was better, may I remind you that no one owns articles in Wikipedia? Asking people to respect your version is just as arbitrary as them asking you to respect the previous version. In that case I think the best course of action would be to revert to the old version of the article (before your rewrite) and resume the discussion from there. Also, discussing your credentials is usually far less effective at convincing people here than discussing the actual content of the article. --Itub 13:26, 17 May 2007 (UTC)[reply]

You have violated Wikipedia policies with that post. You did not wait for consensus before doing a complete rewrite of the article, I don't have to wait for your permission before editing your version. My (or your) qualifications are irrelevant in Wikipedia, only our submissions and sources are. Threatening a revert war is an offence under Wikipedia policies and you will be banned if you do it. If you want to do away with large parts of an existing article, it's your responsibility to cite sources and gather consensus to show they are incorrect/unnecessary. Please maintain civility and discuss which of my edits you find objectionable, like I did. Loom91 13:29, 17 May 2007 (UTC)[reply]

Second try

I am once again replacing the content of this article. The reason for doing this is that the current text contains a very large number or errors, inconsistencies, bad English, misspellings, invalid links, incomplete citations and has an inadequate lead-in. Leaving the article in this state, in the public domain, was a truly irresponsible act.

The material relating to gas-phase equilibria has been expanded a little. It is my belief that nothing essential from the original article has now been left out.

I would also like to emphasise the following points here.

The mass-action derivation of K is unsound. Unsound theories are of historical interest but do not belong in the body of a main article of an encyclopaedia.
I believe it is didactically wrong to teach material that students have subsequently to unlearn. That is why this article is based on thermodynamics, not on the “law” of mass-action.
Individual reaction rates are irrelevant to equilibria except in regard to metastable mixtures and catalysis.
The correct treatment of activity is essential because so many other articles refer to this one. Equilibrium constants determined in a medium of high ionic strength are not approximations. They are true thermodynamic quantities, referring to the medium for standard states, not to a simple aqueous solution. In the real world activity must be taken into account. See, for example, Millero's book on Chemical oceanography.
Errors resulting from the approximation $\Gamma$ =1 are unknowable. I prefer not to give “arm-waving” justifications for this approximation.
If K was determined in an ionic medium, using that value for calculations on aqueous solutions can give seriously erroneous results. There is no such thing as the equilibrium constant for a reaction; each value refers to specific conditions of medium, temperature and pressure (or volume).

Petergans 10:21, 21 May 2007 (UTC)[reply]

I think you need to assume good faith regarding other people's edits and try to understand why they wanted to add what they added, even if it contained errors. I'll focus on one example. One of the sentences that Loom91 added was "Adding a catalyst will fasten the reaction, but it will still stop at the very same point, the equilibrium point". This is an important point that is worth mentioning, and is essentially correct, except for the misuse of the word "fasten" (which means to fix, to attach) to mean something like "accelerate". Yet your version of the article barely mentions catalysts; they only appear in the narrow context of metastable mixtures, and the effect of catalysts on equilibrium and on kinetics is not stated explicitly enough. Such a key concept is worth mentioning in the lead section of the article. As it stands, some readers might wonder whether the statement that catalysts don't affect equilibrium concentrations only applies to the contact process, or whether catalysts only affect metastable mixtures. --Itub 11:34, 21 May 2007 (UTC)[reply]

I don't understand what you mean by " the effect of catalysts on equilibrium" - a catalyst has no effect on equilibrium itself, it affects reaction rates. I took the view that catalysis is adequately dealt with in other articles, but as two of you think it's important I'll rethink how to bring it in. Otherwise, I have strictly avoided mentioning kinetics, which is also covered in other articles and is not directly relevant to equilibrium.

As for the sentence itself, it gave me the impression that catalysts are always needed, which I'm sure was not what the author meant. I have never doubted the good faith of other editors. However, if errors are made I expect the original editor to correct them as we cannot always second-guess what the editor had in mind.

If you want evidence of the fact that I respect previous editors, look at acid dissociation constant which I have just finished cleaning up (there is a request for clean-up on the discussion page).

Petergans 13:33, 21 May 2007 (UTC)[reply]

Maybe I should have said "effect, or lack thereof, of catalysts on equilibrium". I know there is no effect. My point is that I think it is very important to stress that catalysts have no effect on equilibrium, because it is one of the most basic aspects of chemical equilibrium; one that can be taught even at the most introductory level. I think that your version of the article didn't stress this enough, and my guess is that Loom91 didn't either, although I'm certainly not perfect at reading minds. I'm sorry if I questioned your respect for fellow editors. But I don't think you should expect everyone to make only perfect additions, or to correct their own mistakes. Part of the value of Wikipedia in my view is that editor A can add a good point to the article, even if with bad English and without references, and then editor B can add a reference and editor C can fix the language. I don't think the article needs to be perfect at all times, although the more the better. --Itub 13:48, 21 May 2007 (UTC)[reply]

That's a good point. I kind of remember learning it at school. The contact process is a bad example to use here as it does not give an equilibrium mixture. I think it should be replaced by the Haber-Bosch process and linked to Haber-Bosch#ammonia synthesis. Carbonic anhydrase is good. The "metastable" sub-section should be renamed to maybe "Influence of catalysts" and modified to make the point. Any other suggestions? Petergans 17:06, 21 May 2007 (UTC)[reply]

I will only very reluctantly agree with this new Wiki world order of wholesale article replacement but much work needs to be done especially with respect to the large pieces of valid content that have disappeared (just one example: the simple equation delta G = - RTlnK went MIA). First order of business: the opening sentence which according to Wiki lore should contained a concise definition. No need to delete Looms contribution on account of spelling mistakes, not all wiki contributors are native English speakers (myself included) but English is a global language V8rik 20:53, 21 May 2007 (UTC)[reply]

ΔG_m^O = -RT lnK is there in the thermodynamics section, where it is derived from the thermodynamic condition for equilibrium. I understand your reluctance to accept the idea of replacing an article but you must also appreciate that the old article was of such poor quality that it could not be repaired. For instance, there was no derivation of this fundamental equation. I'm not bothered about spelling mistakes. They are easy to correct. What concerns me, above all, is that the science should be right and clearly and unambigously expressed. That has been the purpose of all the changes I have made. The valid content that you refer to has not disappeared. It's all there in substance, if not in exactly the same form.

It would be straightforward to take the definition out of its box and put it at the beginning, but I felt it was better to put it after the bit about Gibbs, because the meaning is clearer when it's there. It's in a box to make it stand out so that people see it immediately. Petergans 22:07, 21 May 2007 (UTC)[reply]

I've just seen the definition that you put in. It is not adequate because it does not cover cases like a mixture of hydrogen and oxygen gases. If you got it out of Atkins and Jones, that's really too bad! In the second sentence " usually" is the wrong concept and what you have written contradicts the satement below that it is a necessary condition. The definition in the Gold book is unclear because the meaning of "ultimately" is unclear. The only clear statement (also in the Gold book)is that ΔG=0 (at constant pressure). In layman's language there is "no tendency ...". Petergans 22:43, 21 May 2007 (UTC)[reply]

Your recent attempt at reverting my edits and mostly impose your original rewrite seems to have been mostly motivated by a desire to have the last say rather than significantly improving the article. You significantly shortened and pushed back the section on minimisation of Gibbs energy while keeping a long section on the mass-balance equations (coincidentally, a section that you wrote). You also seem to have a desire to make this article inaccessible to readers who do not have your expertise by removing the introduction section. As for definitions, I think no matter how big an authority you are on the subject, IUPAC is bigger. Perhaps you should report your objections to their definition (not invalid ones, I agree) to IUPAC, instead of bringing them to a tertiary source like Wikipedia? To address your objections, this is an encyclopedia, not a textbook. We have to report history as well as present. If you continue to revert to your preferred version without prior discussion, it may be interpreted as an execution of your prior threat to start a revert war and you may be blocked from editing Wikipedia. Loom91 07:28, 22 May 2007 (UTC)[reply]

By all means feel free to reintroduce whatever you want, put please, please

Don't introduce inconsistencies of notation

Don't introduce material that directly contradicts something else in the article

Don't split up the lead section but modify as you see fit

Don't introduce time-dependent phenomena. They don't belong here. The equilibrium state is time-independent.

In response to your specific comments, the reason was not personal. As I said above, "the current text contains a very large number of errors, inconsistencies, bad English, misspellings, invalid links, incomplete citations and has an inadequate lead-in." I felt that it would be easiest to revert and make a fresh start.

The section on minimising the Gibbs function was shortened because the mathematical aspect is covered in Lagrange multipliers, just as for the mass-balance equations it is in Newton-Raphson. The former approach is not accessible to the general reader, but the latter is and has been the subject of a vastly greater number of publications. I made a value judgement of the relative significance if the two methods. By the way, I am familiar with Smith's papers on the subject.

Petergans 12:17, 22 May 2007 (UTC)[reply]

The big dilemma

This arises because an obsolete and unsound theory (law of mass-action) is apparently still being taught in schools, but not in Universities. I attempted to address this issue by means of an historical introduction. Perhaps a separate, historical, article on mass-action and kinetics would be better. In this way the details of kinetics could be handled separately from equilibrium.

I'm not sure how sound Mass action is. It appears to confuse the molecularity of a reaction with the rate expression, but I haven't looked at it carefully. The text of the original paper by Guldberg and Waage can be seen in translation.

Showing that the equilibrium state can be approached from either direction was important historically in establishing the nature of the state. This idea could be illustrated by a real isomerisation reaction which is both unimolecular and first order kinetics, or by one of G&W's original subjects of study. BTW, the reaction H₂+I₂ $\to$ 2HI is a chain reaction, not second order, as was originally thought (Atkins).

In summary, put the historical stuff in a separate article?

Petergans 12:17, 22 May 2007 (UTC)[reply]

Writing Equilibrium Equations

I think the article needs to be changed significantly to explain that the exponents in the equilibrium equation are the kinetic order of the reactants in the rate equation, which is not necessarily the same as the coefficient in the balanced reaction equation. The example of how to write an equilibrium equation that's currently in the article seems to imply that, for example, if 2A + B -> C, then Keq must equal [C]/([A]^2[B]). Keq might equal that, if the reaction is second order with respect to A, but you can't know that without actually looking at the rate equation.

RXN quotient

The middle paragraph could possibly be rephrased to better include the mentioning of reaction quotients. - BeardedPhysicist 15:17, 7 Mar 2005 (UTC)

Depth and cohesion in article

I've done a few significant changes to the article in an attempt to give it some more depth and cohesion. Even more depth can be achieved if the involved thermodynamics are exposed in more detail (something I lack knowledge to do). Duplode 5:32, 15 Mar 2005

Constant concentrations

Hi, does anyone know if liquids are also considered to have constant concentration along with solids and solvents? -postglock 01:55, 27 November 2005 (UTC)[reply]

I fixed this a few days ago--yes, pure liquids are considered to have a constant concentration. Hence Kw = [H3O+][OH-], with no water. Olin

Arrow

The arrow in the mock chemical equation should not be used since it is non-standard.

Effects of temperature, pressure and ionic strength on equilibrium?

Have the effects of temperature, pressure and ionic strength on equilibrium be discussed/included/explained anywhere? If not, let's do that, coz this is really important to understanding chemical behaviors in non-standard conditions. Contact: amostai@mit.edu.

"All equilibrium constants depend on temperature and pressure (or volume)" i was under the impression that true thermodynamic equilibrium constants do not depend on pressure (rather on the standard pressure?). would someone please clarify?

ICE

A wikilink to ICE chart needs to placed in this article. s d 3 1 4 1 5 final exams! 17:25, 16 December 2006 (UTC)[reply]

Merging and rewriting

There is lots of duplicated material between here and at Equilibrium constant. I think we should decide to merge some things together, probably in the direction Equilibrium constant --> Chemical equilibrium. Also, would anyone object to a rewrite of this article? We have someone who is potentially interested in doing this. I think it would be a really great thing for this article. --HappyCamper 16:55, 24 April 2007 (UTC)[reply]

merging is a defeatist attitude, better focus on expanding articles. Chemical equilibrium: explain the concept in qualitative terms also suited for laymen. Equilibrium constant: focus on equations and relevant tables. Also many constants describe non-chemical processes. V8rik 17:01, 24 April 2007 (UTC)[reply]

Alright, that sounds good too. Sort of like what we have at quantum mechanics? Sections with brief paragraphs describing concepts, and then a link to a main article which goes into more detail. --HappyCamper 17:26, 24 April 2007 (UTC)[reply]

I'm not in favour of merging. These two topics have different scope. Equilibrium constant is only a specific mathematical idea related to chemical equilibrium. This is like the difference between the scope of the articles quantum mechanics and wavefunction. They are bound to have a lot of overlap, but they are distinctly different topics. Loom91 18:56, 24 April 2007 (UTC)[reply]

So what does this mean? Leave this as is? Or go with V8rik's idea? Am I ever glad I dropped a note here first before being bold...the edit history doesn't betray the fact that there are multiple people watching this article! --HappyCamper 19:46, 24 April 2007 (UTC)[reply]

V8rik has not given a specific example of what he intends to do. But I don't see any problem with the overall idea. Loom91 15:57, 25 April 2007 (UTC)[reply]

I am also not in favor of the merge. I think that the differences between the topics are great enough that they should be treated seperately. Then again, I don't have fancy credentials, so anyone that does, feel free to ignore me. — Preceding unsigned comment added by 76.26.104.63 (talk) 04:24, 1 September 2011 (UTC)[reply]

Entropy of mixing

OK, so it seems there's some contention over this paragraph: [1]. I think the original edit is this one [2], but what is the author really trying to say? I don't see how the justification given connects with the first statement. I'd like to remove this entirely, or at least reword it somewhat. --HappyCamper 19:43, 24 April 2007 (UTC)[reply]

There are some problems with those those paragraphs, but the general idea that equilibrium is due to the entropy of mixing is correct (I'm looking at Atkins and de Paula, 7th edition, p. 226 ["Molecular interpretation 9.1" in the chapter about chemical equilibrium]). However, the entropy increases, not decreases, due to mixing. Also, it would be more general to talk about free energy of mixing. The entropy [times T] and the free energy of mixing are the same only in the case of ideal gases, because in that case the enthalpy of mixing is zero. --Itub 08:09, 25 April 2007 (UTC)[reply]

Actually, it's more general to talk about entropy, because it is a more fundamental and universal quantity than Gibbs energy. The minimisation of the latter is a criterion that can be derived from the maximisation of the former under isobaric conditions. We generally talk about free energies because it's more convenient to look at affairs from the systems perspective rather than the universe's perspective. In standard state, the products of a spontaneous reaction are more favoured (actually, more probable) than the reactants. Yet in ordinary conditions the reaction does not go to completion because the mixing of reactants and products contributes an entropy to the equilibrium state. When an equilibrium is 'driven' by removing the products as they are formed, it's this contribution we are trying to remove. Loom91 16:06, 25 April 2007 (UTC)[reply]

It's more general to talk about entropy only for isolated systems, or the entire universe... but for the mixing process in a non-isolated system, there is a huge difference between entropy and free energy that matters a lot for non-ideal mixtures. It is the enthalpy of mixing and it also contributes to the chemical equilibrium. I also note that the treatment in Atkins uses the free energy of mixing rather than the entropy of mixing when discussing the causes of chemical equilibrium. --Itub 08:18, 26 April 2007 (UTC)[reply]

Let me get a hold of the Atkins book. This is very novel and I want to find out more :-). --HappyCamper 19:13, 26 April 2007 (UTC)[reply]

You miss the point. Get any introductory book on physical chemistry and read the part on Gibbs function. Enthalpy change of the system is simply a more convenient way of expressing the entropy change of the surroundings. The only deciding factor of spontaneuity is entropy change of the universe (or any isolated part of it). The Gibbs function is simply a way of incorporating the entropy change of the surroundings into a system property, the enthalpy change. Loom91 09:07, 27 April 2007 (UTC)[reply]

I know that. The problem is that what people usually call the "entropy of mixing" is what results from the equation

\Delta S_{m}=-nR(x_{1}\ln x_{1}+x_{2}\ln x_{2})\,

(at least in my experience). This equation does not include the change in entropy due to changing the temperature (I assume that's because of the interest in isolating the contribution due to "mixing"); this means that it only applies to an actual mixing process if the process isothermal. What I'm calling the "entropy of mixing" is therefore not equal in general to the total entropy change for the universe and cannot be used a spontaneity criterion by itself ("total entropy change" = "entropy of mixing" + "entropy of cooling/heating due to the mixing process"). A process can only be isothermal if the system is not isolated or if the mixture is ideal. And since people usually care about equilibrium at a given temperature, it is better to talk of the free energy of mixing. If I'm misunderstanding the common usage of the term "entropy of mixing", please give me some references, and feel free to correct the entropy of mixing article as well. --Itub 09:43, 27 April 2007 (UTC)[reply]

But the temperature change is not relevant here. The question is what stops reactions from completely transforming the unfavoured product to the more favoured product? The answer is not in cooling/heating, they will not stop the reaction from going to completion. It is the contribution of mixing that makes the equilibrium state more favoured than the pure product state. Loom91 14:47, 28 April 2007 (UTC)[reply]

New Draft article

I have drafted a new article which you can see at User talk:Petergans/draft.

I propose that the new article should replace both this one on Chemical equilibrium and the article Equilibrium constant. I also intend to write a new article on Stability constant which will deal with metal complexes, chelate effect, databases etc. and possibly another article on [experimental methods] for determining stability constants.

Your comments on these proposals will be welcome. Please post them and any suggestions for improvement etc. to User:Petergans/draft. I will be grateful if you do not edit the article at this stage.Petergans 09:31, 29 April 2007 (UTC)[reply]

Well done. You have come up with a detailed article. But I don't think it's ready to entirely replace the current article. Some objections I have are that you have dived into the detailed thermodynamics right from the start, without a qualitative introduction, say at the high-school chemistry level that is currently present in this article. Your article seems to start at the Thermodynamics section of the current article. It needs the whole qualitative section on equilibrium constant added to its beginning. Secondly, statements such as "this is discussed in blah blah textbook and so will not be discussed here" is not appropriate for an encyclopedia. Please note that the method you have avoided is already present in this article. Thirdly, inline citations are preferred over simply end-of-article references. Fourthly, in the section on aqueous acid-base equilibria it seems better to work with a general Bronsted-Lowry acid/base pair rather than the specific example of ethanoic acid.

Also, I don't see how it can replace the article on equilibrium constant. Your draft in firmly an article on the general topic of chemical equilibrium, rather than the specific tool of equilibrium constant. Also, you did not give a definition of delta-G, which is very non-trivial. Once these are corrected, I think we can complete the rewrite. Loom91 08:58, 30 April 2007 (UTC)[reply]

Thanks for these comments. I'll wait a few days to get more comments before responding in detail. For the present let me say that I don't know what is taught at US high-school level, so I would not know how to pitch for that. Anyway, should we not take an international perspective?

Regarding Equilibrium constant I thought I had covered all the essential points made in that article. I have to say also that the kinetics approach used is completely misguided. The author appears to be aware of this - I quote "But it should be kept in mind that this derivation is valid only for single-step elementary reactions (which are very rare) and not for general reactions where the law of mass action does not apply"!!Petergans 09:48, 30 April 2007 (UTC)[reply]

Stability constant A working draft is now onlinePetergans 15:53, 1 May 2007 (UTC)[reply]

This is not about international or american perspective. Some people may be interested in reading an introduction to the topic of chemical equilibrium without bothering with the thermodynamics. Your draft does not address this segment of the readership. It was also decided ina previous discussion that the articles chemical equilibrium and equilibrium constant should not be merged. Loom91 06:54, 2 May 2007 (UTC)[reply]

In general, I like Petergans's version better that the current one. However, it needs some changes to fit the Wikipedia style better. Most importantly, it needs a lead section before the table of contents to establish context. This is even more noticeable in the current version of the article about stability constants, which starts rather abruptly with "See Chemical equilibrium for definitions and derivations". Please see WP:LEAD for more details about what the article lead should have. Second, sometimes the tone sounds a bit too much like a textbook, with phrases such as "It is easy to see that...", and the tone which sometimes feels a bit too formal or technical. While being correct is obviously important, it is also important to make the article as readable as possible by defining (or wikilinking) technical terms the first time they are introduced in the article. For example, the first time activity is mentioned, there is no link or definition (there is one much later). Same for activity coefficient and ionic strength. I wouldn't mind merging equilibrium constant here, but I don't have a strong opinion either way. --Itub 10:53, 7 May 2007 (UTC)[reply]

Since making my original proposal I have drafted Stability constant and Determination of equilibrium constants. I would now like to modify the proposal as follows: Replace this article by the draft (after style modifications as suggested by Itub) and replace the contents of equilibrium constant by the contents of Stability constant, also after re-styling. Petergans 11:13, 7 May 2007 (UTC)[reply]

My Comments:

I am confused here. In general I do not support whole replacements of articles. I do know that there are no rules against it but it is just not the wikipedia spirit. The article started somewhere in 2001 and since then many people have bothered to contribute and basically you are saying thanks but no thanks.
this page should be about equilibrium in general not just reactions, the iupac definition speaks of processes http://goldbook.iupac.org/C01023.html
the current page also has its virtues, the second section inappropriatly called equilibrium constant (should be: basics) covers a lot of ground, nothing wrong with it.
the problems start with the thermodynamics. I don't understand this section in either the current page or your draft. I certainly do not understand the Sulfur trioxide statement
general remarks already mentioned by itub, draft is lacking a header, subtitles are too long, many relevant internal links not present, no internal links in the text itself, no references to other texts
with respect to the stability constant article I just see a lot of repeated information.

but then again I kind of lost the big picture (what happened to the Nernst equation!). I propose to take it one step at the time and start with the introduction and thermodynamics on this page and take it from there.

Should have signed that as my comment V8rik 19:42, 16 May 2007 (UTC)[reply]

I'm sorry, but I can't see any point in keeping the article stability constant. In that article you treat stability constant as a synonym for equilibrium constant and proceed to give a lot of examples in textbook style, where in standard usage stability constant refers to only a particular type of equilibrium constant. Your draft also falls short as an article on equilibrium constant, since it accomplishes little purpose except give some examples. I think it will be best if you take that article offline for now and concentrate on bringing your draft on chemical eqilibrium upto scratch. Loom91 07:24, 8 May 2007 (UTC)[reply]

I think what we need at this article is a general (as far as possible, non-mathematical) description of the phenomenon of chemical equilibrium. At high school level (at least in France), we approach the idea of equilibrium by pointing out that certain reactions do not go to completion: the example of a weak acid is one possibility, although it should be compared with the strong-acid case to get the idea accross. Other examples include

esterification (historically important in the determination of equilibrium constants)
incomplete oxidation of iron(II) by silver(I) (a favorite in France because the tests for the different ions give you the colours of the French flag!)
synthesis of ammonia from hydrogen and nitrogen (very useful example for a variety of problems when discussing equilibria, such as the fact that the value of the equilibrium constant depends on the way in which you write the reaction equation)

Somewhere in the article, chemical equilibria should be compared with other sorts of equilibrium (mechanical, thermal, ...), and it should be stressed that a chemical equilibrium is dynamic and not static. Physchim62 (talk) 13:23, 22 May 2007 (UTC)[reply]

The discussion is now all over the place, I propose that everybody who has something to say from now on will do it starting at the bottom of the talk page as is customary and also in light of the strongly different views on this topic try to make smaller edits, not changing a bunch of things in one go (and certainly no bold reverts). Thanks. I agree with Physchim62 that the starting level for this page should be high school. This is where Wiki differs from general university level textbook. The French flag example should be included! V8rik 20:55, 22 May 2007 (UTC)[reply]

It's not that some reactions don't go to completion. No reaction (provided the products are not removed from the mixture as they are formed) goes to completion. Some (like dissociation of a strong acid) simply have a very large equilibrium constant. I think an adequate level of non-mathematical introduction is provided by the section titled Introduction. It condenses most of the fundamental material present in a high-school textbook on chemical equilibrium. There are already some examples, will adding more help. I don't think so, but I won't object to a few more examples if they are interesting. Petergan's sections on mathematics are very much needed in a general overview article like this. If an article written purely as a layman's introduction with minimum use of unfamiliar concepts is desired, maybe someone could write Introduction to chemical equilibrium.

Petergans: Please point out what you refer to by

"Don't introduce inconsistencies of notation Don't introduce material that directly contradicts something else in the article Don't split up the lead section but modify as you see fit Don't introduce time-dependent phenomena. They don't belong here. The equilibrium state is time-independent." What are these inconsistencies, contradictions and time-dependent phenomena? As for splitting up the lead section, the wikipedia style manual insists that a lead provide a summary of the main points presented in the article and its size be in proportion to the body of the article. Merging the introduction section with the lead makes it too long and violates house conventions. Loom91 09:20, 23 May 2007 (UTC)[reply]

Some reactions really go to completion in theory, at least if you consider the number of atoms/molecules to be finite. For reactions such as combustion, molar free energies of hundreds of kcal/mol are typical, and correspond equilibrium constants of the order of 10^100 or more. Do the math, and you'll see that the "equilibrium concentration" of the limiting reactant will be less than one atom, even if you start with an amount of substance corresponding to the estimated mass of the universe... --Itub 09:47, 23 May 2007 (UTC)[reply]

You are taking the statistical view. From the thermodynamic point of view the reactants even in a combustion reaction have a non-zero concentration. And even if you do take the statistical view, you can not guarantee that at a given moment there is not a molecule of reactantt left. Calculating using potentials only gives the mean concentration, at the micro-scale there will be significant deviations. Loom91 10:16, 24 May 2007 (UTC)[reply]

I suppose you can never guarantee it, but you can say that the probability of having more than zero molecules of reactant can be ridiculously small. Same as you can "never" guarantee that a radioactive material will decay completely, although in reality they do before 100 half-lives or so. Maybe one of the Fermium atoms made in 1952 still exists! But I'd rather bet my money on wining the lottery four times in a row. --Itub 10:37, 24 May 2007 (UTC)[reply]

Thermodynamics

The previous thermodynamics section in my view lacked an explanation exactly what was being derived (why this chapter exists in the first place). Before that it lacked the introduction of any relationship between Gibbs energy and chemical potential. I have modified this section, I hope it will more clearly demonstrate how you get from standard Gibbs energy equation and relationship chemical potential & activity to the fundamental delta G = lnK/RT. Bear in mind that Wiki is not written specifically for university students and that more steps are required to explain a concept. Also if we ever want this article the get the featured article status (and we all want that!) we really have to dumb down. V8rik 17:44, 31 May 2007 (UTC)[reply]

Notation

Let's have consistency in the symbol used for thermodynamic standard. It should be the plimsoll line. I suggest the use of ..<s><sup>o</sup></s> or <math>..^\ominus</math> as in the following examples. text ΔG^o; math $\Delta G^{\ominus }$ Petergans 10:54, 1 June 2007 (UTC)[reply]

I agree. Loom91 12:03, 1 June 2007 (UTC)[reply]

excellent idea, I will make the necessary changes V8rik 19:17, 1 June 2007 (UTC)[reply]

Ionic strength equation

The equation for ionic strenght differs from that in the ionic strength article, why are there the additional terms c_X and c_Y?

I={\frac {1}{2}}\left(c_{X}+c_{Y}+\sum _{i=1}^{n}c_{i}z_{i}^{2}\right)

V8rik 19:01, 3 June 2007 (UTC)[reply]

The "additional terms" are the contributions from the added salt. Maybe

I={\frac {1}{2}}\left(c_{X}z_{X}^{2}+c_{Y}z_{Y}^{2}+\sum _{i=1}^{n}c_{i}z_{i}^{2}\right)

would be better, with the added comment that z_X and z_Y are (to my knowledge) always equal to one in practice and that then the ionic strength is then effectively equal to the salt concentration. The point about writing the terms separately is that together they will be much larger than the terms due to species in equilibrium, so that ionic strength will be nearly constant, whatever the position of the equilibrium, for example, throughout a weak acid/strong base titration. It is then assumed that the variation in activity coefficients will be negligible and this assumption has been extensively validated by experimental results using the ionic medium method. If you want a reference to back this up you can use [IUPAC SC-Database A comprehensive database of published data on equilibrium constants of metal complexes and ligands] Petergans 08:06, 4 June 2007 (UTC)[reply]

Minimisation of Gibbs energy Caption

This caption is poorly chosen, it does not reflect at all what this section is all about. In my understanding it describes a method for the determination of equilibrium concentrations using Lagrange multipliers. The caption should reflect this V8rik 18:35, 11 June 2007 (UTC)[reply]

It describes a method for the determination of the equilibrium concentrations through a constrained minimization of the free energy, using the method of Lagrange multipliers. Perhaps a more specific section title would be "Minimisation of the free energy using Lagrange multipliers". But the key point is that the concentrations can be obtained from the minimization; the Lagrange multipliers are just part of the method of minimization. I imagine that other methods could be used. --Itub 18:44, 11 June 2007 (UTC)[reply]

The Gibbs energy is minimised subject to the constaint that the equations of mass-balance are satisfied. This was explicit in the version that Loom91 reverted. In any case there is a complete mismatch of notation between the two statements of the mass balance equations (MBEs)

\sum _{j-1}^{m}a_{ij}N_{j}=b_{i}^{0}

T_{A}=[A]+\sum _{i}{p_{i}\beta _{i}[A]^{p_{i}}[B]^{q_{i}}}

Furthermore an important point concerns which parameters are adjusted in the minimisation; this is the real difference between this method and that of section 7.1: when stoichiometric coefficents are one ΔG is a linear function of ln[A] but T_A is a linear function of [A]. This point was lost in the revert. Itub is right, Lagrange multipliers are not essential since there are other methods for constrained minimisation. Incidentally, the treatment as it stands is incomplete. Lagrange multipliers (aka undetermined multipliers) are unknown quantities . The text gives no indication as to how they are determined in this system. Petergans 23:56, 11 June 2007 (UTC)[reply]

If you are all happy with the caption who am i to complain. It is just that to me the content of this section is very unclear to me and it will run into trouble by the time we get to the featured article process. Please expand on its purpose, its input parameters and results and fix the equations if possible. V8rik 19:36, 12 June 2007 (UTC)[reply]

Curtin-Hammett

The statement as it stands is incorrect. Consider a simple equilibrium reaction that can give two products.

A+B

\rightleftharpoons

C; [C]=K₁[A][B]

A+B

\rightleftharpoons

D; [D]=K₂[A][B]

If the system is at equilibrium at all times the product ratio is then given by

{\frac {[C]}{[D]}}={\frac {K_{1}}{K_{2}}}

regardless of any reaction intermediates. The Curtin-Hammett principle applies when the intermediates are not at equilibrium. Suppose the two products are formed from two intermediates X and Y which are formed slowly from A and B. if they are converted rapidly into the products; the concentrations [X] and [Y] will not be the equilibrium concentrations and the product ratio will be as per Curtin-Hammett. This principle is about control of product ratio by means of kinetics and does not belong in an article on equilibria. Petergans 09:21, 17 June 2007 (UTC)[reply]

I agree with you there. The Curtin-Hammett principle is always used in kinetically-controlled reactions. Loom91 08:27, 18 June 2007 (UTC)[reply]

The current Curtin-Hammett principle is consistent with the literature available to me, I made an edit to this effect. If you feel the content of that article contains errors or misrepresents what the principle tries to explain please make the necessary edits but do provide references otherwise the edit will be marked Wikipedia:No original research and reverted. V8rik 19:23, 18 June 2007 (UTC)[reply]

This is not original research. The expression ΔG^o=-RT ln K shows that the equilibrium constant depends on the difference in standard free energies of the reactants and products, independently of the reaction mechanism and of any intermediates that might be involved in that mechanism. Petergans 08:53, 19 June 2007 (UTC)[reply]

(Note: this was a response to V8rik, but Petergans and I posted almost at the same time and there was an edit conflict). The Curtin-Hammett principle article is correct; I know it because I wrote most of it! :P But the question here is whether it is worth mentioning it in the article about chemical equilibrium. Good arguments can be made either way. The situation considered by the Curtin-Hammett principle certainly involves an equilibrium between the two intermediates, but I wouldn't go so far as to say it is an "application" of equilibrium or a "type" of equilibrium; it is more of an application of kinetics. If I mentioned it here, it would be more as an "exception", by saying something like: "when two reactants that are an equilibrium can react irreversibly to give each a different product, the product ratio is not the same as the reactant ratio. This is explained by the Curtin-Hammett principle." This is more or less what you added, but the context is not the best. A similar argument applies to the case of oscillating reactions. I suggest that this article could have a short section near mentioning the existence of kinetics and non-equilibrium thermodynamics. These topics are not completely separable IMO, and at the very least they deserve some mention as related topics. --Itub 09:04, 19 June 2007 (UTC)[reply]

Oscillating reactions

In my opinion this topic is pure kinetics and does not belong here. It is true that the final product in time is an equilibrium mixture, but then that's true of all reactions if one accepts that no reaction ever goes 100% to completion. Petergans 09:53, 18 June 2007 (UTC)[reply]

I have already offered a credible reference regarding this statement. If you feel oscillating reactions are not equilibria or if you insist that equilibria just establish themselves instantaneously please make an edit with a reference confirming your case. Please mind the existing Wikipedia:No original research policies V8rik 19:29, 18 June 2007 (UTC)[reply]

There is no doubt that oscillating reactions belong in the domain of kinetics, since the oscillations are a function of time. My former colleague Steve Scott (http://www.chem.leeds.ac.uk/People/PGB_PDF/SKS.pdf) is an expert in this field so I know more about this topic than you might have imagined. Equilibrium expression do not appear anywhere in the theoretical analysis of the oscillations. See, for example, S.K. Scott, Oscillations, Waves and Chaos in Chemical Kinetics, Oxford University Press, (1994)

To be perfectly clear, the only place where kinetics impinges on equilibria is in catalysis and even in that case there is no effect on equilibrium concentrations. Petergans 08:33, 19 June 2007 (UTC)[reply]

You are placing unnecessary emphasis on the distinction between equilibrium and kinetics. The phenomena of oscillating reactions certainly deserves at leastt passing mention in the article. Loom91 20:48, 19 June 2007 (UTC)[reply]

Why include oscillating reactions when there is no equilibrium content? You can get details of the B-Z reaction at [Scott research group], lecture notes, lecture 4; there is no mention of an equilibrium.

On the more general point, this is an article on chemical equilibrium in an interactive encyclopedia. I believe that a clear distinction should be made, with each topic treated in its own place with links or references as required. Where topics overlap duplication chould be kept to a minimum. Regarding kinetics and equilibrium, there are many instances of equilibrium impinging on kinetics - the Michaelis-Menten mechanism, for example, but the only instance of kinetics impinging on equilibrium is in catalysis. This is an article on equilibria. It should only contain material pertaining to equilibria. Petergans 09:44, 20 June 2007 (UTC)[reply]

Request for comment at Mass action

The article Mass action is currently the subject of an editorial dispute between me and Petergans. I request that you take a look at the revision history and the talk page and participate in the discussion. Loom91 08:21, 28 June 2007 (UTC)[reply]

Image

The text under the image of the burette is misleading, a burette isn't only used for acid-base titrations. I added e.g.

Confusing first sentence

In my opinion, the first sentence is very confusing and spoils an otherwise good article. "In a chemistry, chemical equilibrium is the distribution of interverting chemical compounds." What is that supposed to mean?? Opening sentences should be simple, and I suggest we return to the previous first sentence slightly modified to: "In a chemical reaction, chemical equilibrium is the state in which of the concentrations of the reactants and products do not change with time. (I would delete the mention of activity in the opening sentence, although it can certainly be mentioned later. Dirac66 (talk) 00:24, 7 February 2011 (UTC)[reply]

Steady state

I just read this article after revisiting A-level (highschool) chemistry. There the accepted definition of equilibrium is as given in the opening paragraph: "rates of forwards and reverse reactions equal, concentrations don't change with time." As a theoretical chemist that got me worried, to me that describes steady state and not the very special (interesting) case. The article does go on to describe equilibrium as situtation in which the chemical potential is zero; my wonder is, is it worth making stronger the distinction between steady state and equilibrium? — Preceding unsigned comment added by Bcbccouk (talk • contribs) 17:40, 5 January 2012 (UTC)[reply]

As a start, I have added a "See also" link to Steady state (chemistry) which explains the distinction between the two concepts in the second paragraph. Yes, we can also add something in this article, but that will take more thought to do correctly. Dirac66 (talk) 02:36, 6 January 2012 (UTC)[reply]

Field effects

(moved from User_talk:Petergans#Field_effects_on_equilibrium

Could you insert some formulae concerning electric and magnetic field effects influence on chemical equilibrium?--82.137.11.71 (talk) 19:38, 29 April 2012 (UTC)[reply]

Unfortunately not. I've never heard of any such effects. Petergans (talk) 20:05, 29 April 2012 (UTC)[reply]

Effects occuring in instances like Wien effect and gas phase ion chemistry (for electric field) or for paramagnetic - diamagnetic equilibrium (magnetic field).--82.137.11.134 (talk) 23:20, 29 April 2012 (UTC)[reply]

Entry level

This article could benefit by having an entry level section.
Mis4930 (talk) 02:42, 20 September 2012 (UTC)[reply]

Reference 12

Please check Ref 12. The page cannot be found. — Preceding unsigned comment added by DD dev (talk • contribs) 18:32, 27 November 2012 (UTC)[reply]

I have now updated the URL for this Reference. Dirac66 (talk) 02:56, 29 November 2012 (UTC)[reply]

Pure substances

Regarding the following excerpt from the article: Solids also do not appear in the equilibrium equation. An example is the Boudouard reaction:[10] $2CO\rightleftharpoons CO_{2}+C$ for which the equation (without solid carbon) is written as: $K_{c}={\frac {[CO_{2}]}{[CO]^{2}}}$ In fact, it is common in metallurgy to include the term aC, or activity of carbon, in the Keq expression. The reason is that if we want to calculate the "carbon potential" of a gas containing CO and CO2, we include a term for the aC in the numerator, and knowing the value of Keq, and the partial pressures of CO and CO2, we can calculate the value of the aC. A value of aC = 0.9 can carburize steel. Also, it may be useful to determine the aC in a CO/CO2 mixture to ascertain if the mixture is metastable with reference to the deposition of carbon (i.e., if the aC is >1). Also, this section of the article uses the word "equation" when the words "equilibrium constant expression" are really what is meant. Thermbal (talk) 05:10, 20 June 2013 (UTC)[reply]

I will add the words "if they are considered to be pure". No phase is completely pure, but for many applications it is a reasonable approximation to consider that some phases are pure. For metallurgy, as you say, this is often not the case. Dirac66 (talk) 19:35, 20 June 2013 (UTC)[reply]

Another aspect which can impose the consideration of the activity of solids is the solubility of gases in solids and the underlying adsorbtion equilibrium of gases on solids. In this case it is known that carbon can adsorb considerable amounts of gases.--188.26.22.131 (talk) 10:10, 31 July 2013 (UTC)[reply]

Activity of solids in equlibrium constant is required by dimensional considerations namely the condition that equilibrium constant be dimensionless.--188.26.22.131 (talk) 10:36, 31 July 2013 (UTC)[reply]

Another case of necessity (of metallurgical importance) to consider activities of solids is given by the activity of a metal in an alloy.--188.26.22.131 (talk) 12:58, 31 July 2013 (UTC)[reply]