Talk:Law of mass action

Regarding wording in first paragraph
"Specifically, it implies that for a chemical reaction mixture that is in equilibrium, the ratio between the concentration of reactants and products is constant.

Constant across what? Time? How can you just say something is constant, when it's not clear what it could've been a function of.

Equilibrium constant
Shouldn't the equilibrium constant be equal to [C][D]/[A][B]?

From what I've read, they seem to be swapping products with reactants here.


 * If you read the article more carefully then you will find that the same thing is written there. Loom91 08:59, 9 November 2006 (UTC)

Kinetic order
This seems to be saying that the kinetic order of a reaction with respect to each reactant will always be whatever coefficient goes in font of it in the balanced equation. Is this generally regarded as being correct? Because it's perfectly plausible to have a reaction like A + B -> C that is second order with respect to the concentration of “A”.


 * For a single-step/concerted reaction (the only type for which the Law of Mass Action is valid), the kinetic order of a reactant is indeed equal to its coefficient in the balanced (and correct) stoichiometric equation reduced to its lowest terms. Examples where this is not true all have a multi-step/non-concerted mechanism. Loom91 12:26, 23 January 2007 (UTC)

\ Isn't there another Law of Mass Action thats important in semiconductor physics?? Danski14 18:44, 1 February 2007 (UTC)

Revision
The content of this article is all wrong!!!

I am currently reading the original papers by Guldberg and Waage of 1867 and 1869 in Ostwald's Klassiker der Exacten,Wissenschaften, volume 104, so please leave this article alone until I have finished the revision. There are major discrepancies between what they wrote and what I thought they had written. Petergans 09:53, 20 June 2007 (UTC)


 * May I remind you that no one owns Wikipedia articles. Please point out what parts of this article you consider wrong. Also notice that this article is not solely on the history of Mass Action, so it can not be based exclusively on what Guldberg and Waage had said in 1867 and 1869. Loom91 13:25, 21 June 2007 (UTC)

It ill befits you to patronise me in this way, especially in view of the fact that you have admitted introducing material into another article which you knew to be wrong, a fact that calls into question your integrity. Petergans 19:31, 21 June 2007 (UTC)


 * Your allegation is ridiculous. Good luck getting an admin to support your cause, which seems to be focused more towards intimidating your opponents by flaunting your credentials and asking admins to take action against them than towards conducting reasonable discussions on content. In your post, you didn't say a single word about the article. Loom91 12:58, 22 June 2007 (UTC)

I shall shortly be posting the completed article. It was written after a careful reading of the original papers (in German translation) and is primarily aimed at setting the record straight as to what Guldberg and Waage said and did not say. Many textbooks are in error in this regard.

The article was edited by Loom91 in spite of there being an inuse tag, while I was on a lunch break. This was a rather pointless thing to do since inuse means precisely that the edit was not complete. Since the content of the article is mostly factual, based on the writings on Guldberg and Waage, I expect a discussion here before any further editing of substance will take place.

I also think that the article should be re-named to "Law of Mass Action" and the other uses of "mass action" to be listed on a disambiguation page. The current "different use" should be a separate article. The current redirect page for "mass action" will need to be deleted or made into a disambiguation page. Can anyone more familiar with Wiki help me with these tasks? Petergans 14:25, 23 June 2007 (UTC)


 * You are abusing the inuse template. It should be used in moderation, definitely not when you are on a lunch break. Please refrain from using it unless you are actually editing at that moment. I agree with your rename proposal. Wikipedia is a collaborative system, please learn to respect other editors' contributions and build on them, rather than doing rewrites. Loom91 19:02, 23 June 2007 (UTC)

This is nonsense. You knew that it was I that had put up the inuse tag and the reason for it (see above, para. 2). A consequence of your premature action was that I could not continue as intended since you had rearraged the contents. I therefore had to go back and start from the version before your intervention. Everything that I have written was firmly based on the references cited.

You have now reverted most of the content. Kindly explain why you did this. Petergans 14:36, 25 June 2007 (UTC)

Second revision
There is a fundamental misconception at the heart of this version. The Law of Mass Action is not about kinetics, it is about equilibrium. To find the values of the empirical constants a, b, a’, b’ and k+/k-, as in
 * $$\frac{dx}{dt}=k(p-x)^a(q-x)^b$$

and
 * $$\left( \frac{dx}{dt}\right) '=k'(p'+x)^{a'}(q'+x)^{b'}$$

Guldberg and Waage observed reactions as a function of time in order to have sufficient data to determine all the unknowns. Their objective was always to quantify “chemical affinity”, as is clearly indicated by the titles of their papers.

This misconception was evident in the old versions before 14 May. Other fundamental errors in that version are the statements
 * “proportional to its chemical activity”; must be proportional to concentration.
 * “product of the effective concentrations”; “effective” cannot be correct since reaction rates are always measured as a function of concentration.

These two errors arise from a faulty interpretation of the modern theory of equilibrium constants in terms of kinetics ideas and a misunderstanding of the term “active mass”.. The remainder of the original article was all about kinetics and is irrelevant to the central topic of equilibrium. There was nothing to build on here so a re-write was needed.

The edit by Loom91 on 24 June is not a clean-up, but a mess-up.
 * The emphasis of the article was changed from equilibrium back to the misconceived emphasis on kinetics.
 * The above mentioned errors were re-introduced
 * The article now contains three statements of the law, all different
 * The lead-in, which gave the context has been deleted
 * The reference to other meanings was deleted
 * The expressions in “the law” are inconsistent with the earlier definition of affinity, since exponents are missing
 * Forward and backward reaction rates are shown in terms of activity, not concentration
 * The crucial issues of generalisation and stoichiometric coefficients have been deleted. These define the law of mass action as we know it today.
 * A detailed discussion of kinetics is not needed as equilibrium constants are hardly ever determined by kinetics nowadays.
 * The references to biochemical issues are irrelevant here because they are concerned with the difference in kinetics inside and outside of a cell.
 * There is no “modern” law of mass action. Equilibrium constants are now based thermodynamics and the theory of kinetics has evolved out of all recognition.
 * There are many minor faults such as unnecessary repetition and non sequiturs.

In an attempt to resolve the conflict I have separated the historical and contemporary material. The historical section should not be edited for content (unless the editor has read the original papers) since it is based directly on Guldberg and Waage’s publications.


 * Now I undestand the rationale behind your peculiar editing, it all stems from the fundamental misconception that the law of mass action is about equilibrium rather than kinetics. The law of mass action is a stement about rates of reactions (as can be verified from the countless textbooks available in the market), so it is firmly a law of kinetics. Equilibrium considerations are secondary. I stress again that this article is not (solely) about the historical development of the law as you seem to think. Merely writing from the outdated papers will not give a balanced article. The law of mass action is firmly about kinetics. The small errors you point out can be cleaned up without messing up the whole article. To discuss your points:


 * Your lead was perhaps the most atrocious section of the article. It seemed to start at the middle of a history textbook, completely lacking any context or summarisation of article. I suggest you review Wikipedia's community style guides to see what leads are supposed to be like.
 * The whole concentration/activity issue has been discussed in the article itself.
 * I do not see that stoichiometric coefficients have been deleted. They are very much present in the article.
 * I've no particular fondness for the biochemical section. Perhaps we should retain a line or two as an illustration and delete the rest.


 * All the other points you raised are based on your strange idea that for some reason the law of mass action is about equilibrium. Unfortunately, your view is not supported by standard and reputable sources. May I suggest that you implement any proposed changes one part at at a time instead of starting anew every time. Loom91 08:16, 28 June 2007 (UTC)


 * By the way, your description of me as a loose cannon is rather amusing ;-) If you look carefully at the diffs (as I do) then you will find that little of the actual content you added has been reverted. I've mostly reorganised, cleaned-up and added back sections you had deleted. Loom91 08:31, 28 June 2007 (UTC)

I don't want to get involved too much in this dispute because I still don't really know what the law of mass action is. It seems to me that it is an old name loosely used in some circles, but for example Atkins doesn't mention it at all in his book Physical Chemistry. But in case it helps, look at this book found in Google Books:. It clearly makes a distinction between a "kinetic law of mass action" and an "equilibrium law of mass action" near the bottom of page 72. --Itub 09:27, 28 June 2007 (UTC)

Also note that the book I referenced has a quote from Berthollet, 1803, where he says that the chemical activity depends not only on the affinity, but also on the mass. Therefore the statement in the current version of this article that 'the "chemical affinity" or "reaction force" between A and B did not just depend on the chemical nature of the reactants, as Berthollet and others has supposed,' is incorrect. --Itub 09:51, 28 June 2007 (UTC)

Two more articles worth reading: Guggenheim, E. A. Textbook errors. guest column J. Chem. Educ. 1956, 33, 544. and Lund, E. W. Guldberg and Waage and the law of mass action. J. Chem. Educ. 1965, 42, 548. --Itub 10:23, 28 June 2007 (UTC)

Equilibrium constant
Shouldn't the equilibrium constant be equal to [C][D]/[A][B]?

From what I've read, they seem to be swapping products with reactants here.


 * If you read the article more carefully then you will find that the same thing is written there. Loom91 08:59, 9 November 2006 (UTC)

Kinetic order
This seems to be saying that the kinetic order of a reaction with respect to each reactant will always be whatever coefficient goes in font of it in the balanced equation. Is this generally regarded as being correct? Because it's perfectly plausible to have a reaction like A + B -> C that is second order with respect to the concentration of “A”.


 * For a single-step/concerted reaction (the only type for which the Law of Mass Action is valid), the kinetic order of a reactant is indeed equal to its coefficient in the balanced (and correct) stoichiometric equation reduced to its lowest terms. Examples where this is not true all have a multi-step/non-concerted mechanism. Loom91 12:26, 23 January 2007 (UTC)

\ Isn't there another Law of Mass Action thats important in semiconductor physics?? Danski14 18:44, 1 February 2007 (UTC)

Revision
The content of this article is all wrong!!!

I am currently reading the original papers by Guldberg and Waage of 1867 and 1869 in Ostwald's Klassiker der Exacten,Wissenschaften, volume 104, so please leave this article alone until I have finished the revision. There are major discrepancies between what they wrote and what I thought they had written. Petergans 09:53, 20 June 2007 (UTC)


 * May I remind you that no one owns Wikipedia articles. Please point out what parts of this article you consider wrong. Also notice that this article is not solely on the history of Mass Action, so it can not be based exclusively on what Guldberg and Waage had said in 1867 and 1869. Loom91 13:25, 21 June 2007 (UTC)

It ill befits you to patronise me in this way, especially in view of the fact that you have admitted introducing material into another article which you knew to be wrong, a fact that calls into question your integrity. Petergans 19:31, 21 June 2007 (UTC)


 * Your allegation is ridiculous. Good luck getting an admin to support your cause, which seems to be focused more towards intimidating your opponents by flaunting your credentials and asking admins to take action against them than towards conducting reasonable discussions on content. In your post, you didn't say a single word about the article. Loom91 12:58, 22 June 2007 (UTC)

I shall shortly be posting the completed article. It was written after a careful reading of the original papers (in German translation) and is primarily aimed at setting the record straight as to what Guldberg and Waage said and did not say. Many textbooks are in error in this regard.

The article was edited by Loom91 in spite of there being an inuse tag, while I was on a lunch break. This was a rather pointless thing to do since inuse means precisely that the edit was not complete. Since the content of the article is mostly factual, based on the writings on Guldberg and Waage, I expect a discussion here before any further editing of substance will take place.

I also think that the article should be re-named to "Law of Mass Action" and the other uses of "mass action" to be listed on a disambiguation page. The current "different use" should be a separate article. The current redirect page for "mass action" will need to be deleted or made into a disambiguation page. Can anyone more familiar with Wiki help me with these tasks? Petergans 14:25, 23 June 2007 (UTC)


 * You are abusing the inuse template. It should be used in moderation, definitely not when you are on a lunch break. Please refrain from using it unless you are actually editing at that moment. I agree with your rename proposal. Wikipedia is a collaborative system, please learn to respect other editors' contributions and build on them, rather than doing rewrites. Loom91 19:02, 23 June 2007 (UTC)

This is nonsense. You knew that it was I that had put up the inuse tag and the reason for it (see above, para. 2). A consequence of your premature action was that I could not continue as intended since you had rearraged the contents. I therefore had to go back and start from the version before your intervention. Everything that I have written was firmly based on the references cited.

You have now reverted most of the content. Kindly explain why you did this. Petergans 14:36, 25 June 2007 (UTC)

Second revision
There is a fundamental misconception at the heart of this version. The Law of Mass Action is not about kinetics, it is about equilibrium. To find the values of the empirical constants a, b, a’, b’ and k+/k-, as in
 * $$\frac{dx}{dt}=k(p-x)^a(q-x)^b$$

and
 * $$\left( \frac{dx}{dt}\right) '=k'(p'+x)^{a'}(q'+x)^{b'}$$

Guldberg and Waage observed reactions as a function of time in order to have sufficient data to determine all the unknowns. Their objective was always to quantify “chemical affinity”, as is clearly indicated by the titles of their papers.

This misconception was evident in the old versions before 14 May. Other fundamental errors in that version are the statements
 * “proportional to its chemical activity”; must be proportional to concentration.
 * “product of the effective concentrations”; “effective” cannot be correct since reaction rates are always measured as a function of concentration.

These two errors arise from a faulty interpretation of the modern theory of equilibrium constants in terms of kinetics ideas and a misunderstanding of the term “active mass”.. The remainder of the original article was all about kinetics and is irrelevant to the central topic of equilibrium. There was nothing to build on here so a re-write was needed.

The edit by Loom91 on 24 June is not a clean-up, but a mess-up.
 * The emphasis of the article was changed from equilibrium back to the misconceived emphasis on kinetics.
 * The above mentioned errors were re-introduced
 * The article now contains three statements of the law, all different
 * The lead-in, which gave the context has been deleted
 * The reference to other meanings was deleted
 * The expressions in “the law” are inconsistent with the earlier definition of affinity, since exponents are missing
 * Forward and backward reaction rates are shown in terms of activity, not concentration
 * The crucial issues of generalisation and stoichiometric coefficients have been deleted. These define the law of mass action as we know it today.
 * A detailed discussion of kinetics is not needed as equilibrium constants are hardly ever determined by kinetics nowadays.
 * The references to biochemical issues are irrelevant here because they are concerned with the difference in kinetics inside and outside of a cell.
 * There is no “modern” law of mass action. Equilibrium constants are now based thermodynamics and the theory of kinetics has evolved out of all recognition.
 * There are many minor faults such as unnecessary repetition and non sequiturs.

In an attempt to resolve the conflict I have separated the historical and contemporary material. The historical section should not be edited for content (unless the editor has read the original papers) since it is based directly on Guldberg and Waage’s publications.


 * Now I undestand the rationale behind your peculiar editing, it all stems from the fundamental misconception that the law of mass action is about equilibrium rather than kinetics. The law of mass action is a stement about rates of reactions (as can be verified from the countless textbooks available in the market), so it is firmly a law of kinetics. Equilibrium considerations are secondary. I stress again that this article is not (solely) about the historical development of the law as you seem to think. Merely writing from the outdated papers will not give a balanced article. The law of mass action is firmly about kinetics. The small errors you point out can be cleaned up without messing up the whole article. To discuss your points:


 * Your lead was perhaps the most atrocious section of the article. It seemed to start at the middle of a history textbook, completely lacking any context or summarisation of article. I suggest you review Wikipedia's community style guides to see what leads are supposed to be like.
 * The whole concentration/activity issue has been discussed in the article itself.
 * I do not see that stoichiometric coefficients have been deleted. They are very much present in the article.
 * I've no particular fondness for the biochemical section. Perhaps we should retain a line or two as an illustration and delete the rest.


 * All the other points you raised are based on your strange idea that for some reason the law of mass action is about equilibrium. Unfortunately, your view is not supported by standard and reputable sources. May I suggest that you implement any proposed changes one part at at a time instead of starting anew every time. Loom91 08:16, 28 June 2007 (UTC)


 * By the way, your description of me as a loose cannon is rather amusing ;-) If you look carefully at the diffs (as I do) then you will find that little of the actual content you added has been reverted. I've mostly reorganised, cleaned-up and added back sections you had deleted. Loom91 08:31, 28 June 2007 (UTC)

I don't want to get involved too much in this dispute because I still don't really know what the law of mass action is. It seems to me that it is an old name loosely used in some circles, but for example Atkins doesn't mention it at all in his book Physical Chemistry. But in case it helps, look at this book found in Google Books:. It clearly makes a distinction between a "kinetic law of mass action" and an "equilibrium law of mass action" near the bottom of page 72. --Itub 09:27, 28 June 2007 (UTC)

Also note that the book I referenced has a quote from Berthollet, 1803, where he says that the chemical activity depends not only on the affinity, but also on the mass. Therefore the statement in the current version of this article that 'the "chemical affinity" or "reaction force" between A and B did not just depend on the chemical nature of the reactants, as Berthollet and others has supposed,' is incorrect. --Itub 09:51, 28 June 2007 (UTC)

Two more articles worth reading: Guggenheim, E. A. Textbook errors. guest column J. Chem. Educ. 1956, 33, 544. and Lund, E. W. Guldberg and Waage and the law of mass action. J. Chem. Educ. 1965, 42, 548. Itub 10:23, 28 June 2007 (UTC)


 * The comments from Itub resulted in edit conflicts so I have only saw them after writing the stuff below. Berthollet's comment in 1803 comes after the work of G&W was accepted by Van't Hoff. In 1864 G&W were referring to the 1862 paper by Berthollet and St. Giles. There is a long historical introduction in the 1879 paper which puts all this in context. Maybe the wording should be amended to "as Berthollet and others had supposed prior to 1864". I'll have a look at the J. Chem. Ed articles. I don't have access to electronic journals here, so it would save me a trip to the University if I could be sent pdfs by e-mail.


 * For Loom91:


 * It is not just me that thinks that equilibrium is the key issue. I quote from Vogel's Textbook of Quantitative Analysis, 6th edition, section 2.1, entitled "The law of mass action":
 * "Guldberg and Waage (1867) clearly stated the law of mass action (sometimes called the law of chemical equilibrium)..."


 * The rest of the section is about equilibrium constants. It is true that the law can be given as a statement about "the velocity of a reaction", but that's not the point. The significance of the work of G&W is that by recognising forward and backward reaction velocities to be equal at equilibrium they were able to derive, from the law on velocities, what we now call an equilibrium constant, for the first time in the history of chemistry. All the systems they investigated were equilibrium systems. Don't belittle their work. It is an important piece of chemical history which had a big impact in its time. Having said that, it is of little or no relevance today. The theories of equilibrium constants and reaction rates have moved on, rendering the law of mass action to be, to all intents, obsolete (hence no mention in Atkins). What do you think is of contemporary relevance?


 * Regarding stoichiometric coefficients, what you deleted was the explicit reference. Perhaps you did not appreciate that the exponents in the 1864 theory were not stoichiometric coefficients. Abegg makes the specific comment on the 1879 paper that this was the first time that reaction stoichiometry was made part of the law of mass action. I am very careful about what I write, revising it over a period of days in a "sandbox", for clarity, correctness and coherence. Petergans 11:00, 28 June 2007 (UTC)


 * There seems to be some confusion between Berthollet and Berthelot. It was the latter who published with St. Gilles. However, Berthollet predated them both by a long time; he died in 1822 and the quote I'm referring to is from 1803 (perhaps you thought it was a typo and meant 1903?). --Itub 11:20, 28 June 2007 (UTC)

Just two more points at this stage. We all agree that reaction rates are not, in general, proportional to concentration. If that was all, the law of mass action would not be held in any esteem. It's the application to equilibria that makes it significant.

I have read the two articles, Guggenheim, E. A. Textbook errors. guest column J. Chem. Educ. 1956, 33, 544. and Lund, E. W. Guldberg and Waage and the law of mass action. J. Chem. Educ. 1965, 42, 548. They confirm that what I had written is correct. Petergans 13:00, 28 June 2007 (UTC)

Second reversion
This is becoming farcical. Leaving aside, for the moment, the fact my edit been reverted again, you have simply ignored the points made earlier an re-introduced a load of errors. To give but one example, there are three definitions of the law, each different.
 * 1) The rate of a chemical reaction is proportional to [the] probability that the reacting molecules will be found together in a small volume
 * 2) The rate of a chemical reaction is directly proportional to the product of the effective concentrations of each participating molecule
 * 3) When two reactants, A and B react together at a given temperature in a "substitution reaction" the affinity, or chemical force between them, is proportional to the active masses, [A] and [B], each raised to a particular power

Definition 1 is a re-interpretation of the law, not a statement of it. The term "small volume" is vague, whereas G&W explicitly talked about "collision frequency". "Raised to a power" is missing.

In definition 2 the word effective is wrong. "Raised to a power" is missing. Also this statement is not valid for heterogeneous equilibria.

Definition 3 is taken directly from the work of Guldberg and Waage.

This kind of slapdash editing does not help to produce a good article. In fact it hinders the process. You must take more care with your edits to make sure that you don't introduce anomalies like this one. The other points still stand unanswered.

On the substantive issue of the law of mass action, this is what Guggenheim says at the end of his article on texbook errors.

"To sum up, to Guldberg and Waage belongs the credit of being the first to appreciate quantitatively the nature of a balanced reaction. But they did not succeed in correctly formulating a quantitative expression for the equilibrium condition until six years after Horstmann had done so for gases and two years after Van't Hoff had done so for ester hydrolysis. They made no significant contribution either experimental or theoretical to our knowledge of kinetics"

I hope you know that Guggenheim is as major authority in the the field of thermodynamics. Note that the topic of the law of mass action is well known to be a source of text-book errors (see also K.J. Mysels, J. Chem. Ed., (1956), 33, 178).

PDFs briefly available
I have placed the two articles together with a third one (Mysels) on a private web page on my web site. Loom91, please confirm when you have downloaded the PDF files as I must remove this page within a few days in order not to breach copyright since Wikipedia is in the public domain. After you have read these papers you must surely agree that the emphasis on the rate law of mass action is "misplaced". I suggest that we then revert to my last posting and proceed from there, improving the lead-in etc. etc. Petergans 09:31, 29 June 2007 (UTC)


 * I'm afraid I don't fully agree with your interpretation of these papers. For instance, Mysels says:


 * Guldberg and Waage in their study of chemical affinity formulated the law of the rate of chemical reactions as proportional to the "active mass" of the reagents. This they called the law of mass action and very clearly defined "active mass" as amount per unit volume. From this they also deduced as a clearly separated proposition the "condition of equilibrium" which is the conventional form of the equilibrium constant. (emphasis mine)


 * I agree however with your opinion that there is no "modern" law of mass action. It may be true that G&W were interested in equilibrium and derived it from kinetics, but at least according to the quote above, by "law of mass action" they were referring to the kinetic law.--Itub 09:52, 29 June 2007 (UTC)

This is why there is so much confusion. This is what G&W wrote in the 1879 paper.

"When two substances A and B interact with each other to form two new substances A' and B', the chemical force with which A and B act upon each other can be measured by the amount of the new substances produced in unit time. ... The chemical force with which the two substances A and B act upon each other is equal to the product of their active masses multiplied by the affinity coefficients." (my emphasis)

The affinity constant was defined as the proportionality constant according to the amount of A' and B' produced in unit time. They go on to say that the condition for equilibrium is that the chemical forces should be equal.

Later on they state:

"The speed with which the new products are produced can be ascertained in the following manner. When the the number of molecules of A and B in unit volume is denoted by p and q the collisions frequency is proportional to pq. ... This treatment, which is known from from the theory of dissociation of gases, can be extended to be generally applicable to all phases. ... φapbq = kpq ... φab = k"

φ is a rate constant, and a and b are factors for the the fraction of collisions that result in reaction. What comes out of this reading is that the law of mass action in terms of reaction rates was not exactly original, being modelled on collision theory for gases, and that the purpose of measuring reaction rates was to obtain values for the affinity constants in order to quantify equilibria. Thus, the significance of the work of Guldberg and Waage lies not in the rate law itself, but the use they made of it. Petergans 14:04, 29 June 2007 (UTC)


 * I think a lot of this confusion is resulting from the fact that the law of mass action is not, and never was, something clearly defined and set in stone (unlike, say, Schrodinger's equation). It was originally based on an inadequate (from a modern viewpoint) understanding of chemistry. Over time, different authors have interpreted it to suit their needs and to be consistent with contemporary chemistry. It is undeniable that even originally it was a statement about the rates of chemical reactions, even if the authors emphasised equilibrium aspects. Modern elementary texts focus entirely on the kinetic approach, deriving equilibrium from different considerations. This confusion is inherent in the literature. The best we can do is to clearly distinguish its history from whatever can be salvaged of it today. The main problem, IMO, with Petergan's writing is that it suffers from the typical problem of an academic: it does not provide sufficient introduction and context for the layman. Perhaps Itub could take the content and try writing the article. Loom91 20:25, 30 June 2007 (UTC)


 * I'll pass, thanks. --Itub 07:59, 2 July 2007 (UTC)

I agree with most of what Loom91 says, but with one significant difference. Having looked again at all the papers published by G&W, it is likely that the confusion arises, at least in part, from the fact that statements of the law changed from 1864 to 1867 to 1879. I have therefore revised the text to make this more apparent. I have tried to represent fairly some of the apparently conflicting views that have been expressed on this talk page. I have also tried to put everything in context. The lead-in is perhaps too brief, but it's the best that I could think of.

I have put a lot of effort into this revision. May I make a fervent plea that its shortcomings be discussed here before changing the text. By working together we can do much better than by working as individuals. And, please, let's have no more silly personal attacks like the one at the end of Loom91's most recent post. Petergans 20:03, 2 July 2007 (UTC)

Please stop this!
Petergans, please stop this revert war. Wikipedia is a collaborative project, and you must learn to respect the work of other editors. You have been told more than once in the past that nobody owns an article, and yet you insist on overwriting anything not written by you. After your last rewrite, I left the historical section completely alone because I know nothing about that, instead confining my edits to the lead and the contemporary section. But you were still not satisfied. You insist on recreating the history section in the lead, without giving any context or introduction. Unfortunately, this is NOT in accordance with Wikipedia style conventions. Unless you can gather community consensus to change guidelines regarding article leads, I'm afraid your edits are not acceptable.

You also insist on packing the contemporary section with irrelevant information about equilibrium calculation, when clearly all modern references to the law of mass action treat it as a kinetic postulate. I understand that equilibrium thermodynamics is your specialisation, but that does not mean you have to put in your knowledge where it does not belong. I think this has gone on long enough. If rewriting articles completely with no regard for other people's work is the only way you can edit, then I'm afraid Wikipedia is not the right place for you. Perhaps you will feel more at home writing a traditional encyclopedia. I understand that as an expert it may be frustrating to see your work edited by people with no traditional qualification, but that's the way Wikipedia works. You can take it or leave it, but edit warring will not change anything. Edit responsibly and we can reach a satisfactory conclusion. Loom91 11:55, 6 July 2007 (UTC)


 * I'm not going to comment on whether the law of mass action is about kinetics or about equilibrium, but I have to agree with Loom91 that Petergans's latest version of the lead did not comply with Wikipedia style. My view of the guidelines is that the very first sentence of the article should serve two purposes: 1) to put the topic into context. The rule of thumb is that a reader that comes here randomly should be able to say at least something like "oh, this has something to do with chemistry" from reading the first sentence. 2) To define the topic in a very concise way. The version of the lead in question started with the sentence "The Law of Mass Action was first proposed by Guldberg and Waage in 1864 but was modified in subsequent papers." While this is a perfectly good sentence to begin a history subsection, it fails for the beginning of the lead section on both counts. A reader will have no clue about what the law is about, or what the law is.


 * To be constructive, I'll propose an alternative sentence: "In physical chemistry, the law of mass action was proposed in the late 19th century to explain the chemical forces that drive reactions towards equilibrium in terms of the 'active mass' of the reactants." As a second sentence, or somewhere else in the lead, I would add something like "This law was historically important because it helped understand the dynamic nature of chemical equilibrium, but it was replaced by modern chemical kinetics and thermodynamics once its limitations became known." My point of view here is that the law is historically important but is not a "real" law in modern chemistry, and that this should be emphasized in the lead so that a casual reader won't get the wrong impression that this is a modern law. These sentences don't need to be included verbatim, but I hope they will give you an idea of what I think should be included in the lead. --Itub 12:59, 6 July 2007 (UTC)


 * Good suggestions, but I will like to contest the point that LMA is not a modern law. Concerted reactions do obey the law. In fact, a way of testing mechanisms is to apply LMA to each individual step and then perform mathematical approximations to derive the overall theoretical rate law for the composite reaction. By comparing this to the observed rate law, mechanisms may be discarded. This is the point I've been trying to make throughout. Loom91 13:24, 6 July 2007 (UTC)


 * To me it's not modern in the sense that many modern textbooks don't even use that name. The ones who mention it are usually engaging in a sort of "revisionist nomenclature", and they don't even do it consistently. For a simple reaction A <-> B, some use the name "law of mass action" for dA/dt = -kA, some for dA/dt = -k1A + k2B, and some for K = B/A. That's where all the confusion comes from. --Itub 13:37, 6 July 2007 (UTC)


 * I've seen the name LMA used only for the first equation. The third usually goes by the name law of chemical equilibrium. In science, revisions always happen. Many terms change their meaning to various extents. Loom91 13:56, 6 July 2007 (UTC)

I will just make one point at this stage. I believe, like Itub, that the LMA is of purely historical interest. My objective was to present the history as accurately as possible, especially in view of the way it has been frequently mis-represented and even distorted. My "interpretations" at the beginning and end were intended to relate purely to the original papers by G&W and to place their work in its historical context. Petergans 19:31, 6 July 2007 (UTC)

Science issue
This is an issue of science, not personality. The response above ("Good suggestions") pinpoints the area of disagreement. No-one denies that G&W used kinetics and that the LMA can be expressed as postulate concering kinetics. However, the current lead-in is inconsistent with the history section and two important points are missed:
 * 1) G*W used kinetics to determine what they called the ratio of affinity coefficients. They did not determine individual affinity coefficients. Nowadays we would call an affinity coefficient a rate constants and the ratio an equilibrium constant. Their lasting contribution to the development of chemistry was to characterise equilibria both qualitatively and quantitatively.
 * 2) The rate equation for a concerted reaction v=k(A][B] was obtained independently by Van't Hoff in the late 19th century. It is a coincidence that this rate equation was also used by G&W. It is Van't Hoff who made the lasting contribution to the development of chemical kinetics by giving rate expressions not only for this type of reaction but for other types too, that is, for developing the theory of rate expressions and techniques for using them such as initial slope measurements. Of course complex reaction kinetics are modelled by considering the individual reaction steps, but this has nothing to do with Guldberg and Waage. In fact E.A. Guggenheim has stated that G&W "made no significant contribution either experimental or theoretical to our knowledge of kinetics". Indeed, their experimental work was almost entirely on heterogeneous systems!!! It is therefore wrong to associate modern kinetic studies with the LMA.

I quote from Loom91 above: "The best we can do is to clearly distinguish its history from whatever can be salvaged of it today". I differ only in believing that the LMA is obsolete and that nothing needs to be salvaged as the work of G&W was outstanding in its historical context.

Now, a detailed analysis why the current lead-in is most unsatisfactory.
 * 1) In chemistry, the law of mass action is a postulate concerning the relation between the amount of reactants and the rate of the reaction. This is incorrect. The first postulate was the chemical affinity was proportional to a product of active masses. Later they postulated that reaction rate would be proportional to chemical affinity, that is, to a product of active masses.
 * 2) Active mass may be taken to mean activity This is a classic text-book error. As has already been pointed out activity belongs in the field of thermodynamics and has no place in kinetics.
 * 3) though the original interpretation was closer to concentration (for homogeneous reactions). It was not "closer to", it was explicitly defined as concentration.
 * 4) However, this postulate is necessarly true only for a specific type of reactions and can not be applied indiscriminately. The LMA would not be worth remembering if this were true. In fact it only applies to the kinetic postulate and this really does not matter as, at equilibrium, forward and backward reaction rates are equal regardless of the nature of the rate expression which may apply. Why has the reference to their recognition of the dynamic nature of chemical equilibrium been deleted from the lead-in?

In conclusion I would make these points.
 * Secondary sources, such as text-books, are always less reliable that primary sources. That is why I have based the history section on the primary source material. In regard to this particular topic we are all agreed that there is confusion in the literature. Would it not therefore be best to limit the article to the work of G&W and a critical assessment of that work?
 * Although the concept of chemical affinity is outdated, this was the focus of all the work that G&W did. Not for nothing do all their papers contain the word affinity. To present their work in terms of kinetics is wrong in principle because they did not determine rate constants, but a ratio of rate constants.
 * I expect you guys to take note of these points and to amend the article in the light of them. Look carefully at the material that was deleted in the last reversion and put back what is relevant. If you do not do the job yourselves you will leave me no option but to do it myself in whatever way I think best. Petergans 11:03, 9 July 2007 (UTC)


 * Wikipedia, being a tertiary source, must reflect all aspects of the topic. There is a postulate, used in modern textbooks, that says the rate of a single-step reaction is proportional to the concentrations of the reactant molecules. This is very distinct in concept from the original LMA, but nevertheless it is given the name LMA. It is not very good terminology and creates confusion, but the fact remains that it is used. We must reflect that in our article. If you think that history is not represented well in the lead, then add a section summarising the main historical points. My point is that the article must not exclusively be about history, because there does exist a modern usage of the name Law of Mass Action, hhowever distinct that may be from the historical interpretation. Loom91 12:02, 9 July 2007 (UTC)


 * Some textbooks do use the words "law of mass action" to refer to what I would call "definition of equilibrium constant". See for example, , , , . However, I admit that I found more results that use the name to refer to the rate equation for an elementary step (see the other search results for the queries I refer to; in any case, whatever statement you make about the "modern" law of mass action should be referenced). But I strongly object to calling it a "postulate". I don't know if the original articles presented it as a postulate, but in modern chemical kinetics it is either considered an empirical law, or it is based on more fundamental theories of statistical mechanics. --Itub 13:10, 9 July 2007 (UTC)


 * What is the difference between a postulate and an empirical law? An empirical law is something that can not be derived from some more fundamental theory but can be verified by experiment. That also seems to be the meaning of a postulate. Newton's laws of motion are usually called postulates, though they can be derived as a macroscopic limit of quantum mechanics. Loom91 06:16, 10 July 2007 (UTC)


 * Please give me titles and authors of the text-books referred to in the paragraph beginning "Wikipedia, being a tertiary..." Petergans 17:21, 9 July 2007 (UTC)


 * Take a look at Itub's post above me, where he says "However, I admit that I found more results that use the name to refer to the rate equation for an elementary step" . I can give a couple of references (K. L. Chugh, Maity and Ganguly), but they are not very well-known on a global scale and I will prefer if someone found a more standard text to cite. Loom91 06:16, 10 July 2007 (UTC)

Postulates are statements that are assumed to be true without proof, and are used when a theory is developed deductively. Some physical theories are sometimes, but not always, presented in this fashion (thermodynamics, relativity, and quantum mechanics; I have never seen Newton's laws presented as postulates, but I supposed you could look at them that way). But I don't recall any theory in chemistry commonly being presented in such a way (I would love to hear some examples!). --Itub 07:45, 10 July 2007 (UTC)
 * How about Hammond's postulate? Loom91 09:34, 10 July 2007 (UTC)
 * Ok, there's one. :) But I'm still not convinced that the law of mass action should be considered a postulate. Again, one can find a few books that use that word, but they are in the minority. --Itub 10:14, 10 July 2007 (UTC)


 * (COPY) (K. L. Chugh, Maity and Ganguly), but they are not very well-known on a global scale and I will prefer if someone found a more standard text to cite. Loom91 06:16, 10 July 2007 (UTC)

The point is, this alternative definition of a LMA needs to be properly sourced. Text-book writers usually summarise contemporary knowledge, they don't usually invent ideas. So, please someone find a more standard source so that this can be written up properly. In any case I suggest that, to minimise confusion, the modern stuff should be placed in a completely separate section from the historical stuff. I would go further and say that it should not be presented in detail until it has been properly sourced. A short summary with a reference to this book (title please!) would be enough.

The bulk of this article is about the work of Guldberg and Waage as this is what has been generally perceived to be the origin of the LMA. A single statement of the law is not viable. In any case the nature of the "law" is less important than the use to which G&W put it, which was the study of equilibria. Kinetic measurements were used in order to study these equilibria, just as today pH or absorbance measurements would be used. That's the historical fact. Petergans 20:30, 10 July 2007 (UTC)

I have now looked at the results of the Google search done by Itub. References to kinetics are all of the form that "elementary reactions" follow the law of mass action. The implication here is that the law has the form v=k[A][B]. Loom91 says "There is a postulate, used in modern textbooks, that says the rate of a single-step reaction is proportional to the concentrations of the reactant molecules. This is very distinct in concept from the original LMA". I don't see this as a distinct concept as it is consistent with G&W, 1879; "elementary" reactions follow the rate expression v=k[A][B]. In the 1867 section of the article it is stated that
 * "The rate of a reaction is proportional to the product of the active masses of the reagents involved.

This is an alternative statement of the Law of Mass Action." The kinetics of elementary reactions are entirely consistent with this. Petergans 10:54, 11 July 2007 (UTC)

As far as I can tell, the modern stuff are separate from the history. This discussion is getting somewhat disordered, I no longer see the exact point of disagreement. Let's try to order it somewhat. Do you or do you do not agree that LMA is used by many modern textbook suthors to describe the principle that kinetics of elementary reactions follow the chemical equations? If you do, then what change do you desire? Loom91 21:02, 11 July 2007 (UTC)

When you say that the law of mass action "can no longer be considered valid in general", you must be super-duper clear about which equation you are talking about. The K equation is valid, under all circumstances. The rf equation is only valid sometimes. This topic is confusing enough in general, without having a bunch of chemistry students thinking there is a mistake in their textbook, and the equilibrium constant equation is wrong. The "mistake" in textbooks is (perhaps) which equation the LMA refers to, and not the equilibrium constant equation itself. The reason professors are still teaching the law of mass action is because they are talking about the equation / conditions when it is correct. LMA is not some historical curiosity like Lamarckian evolution. There is a reason the former is still taught, while the latter is not. Just my 2 cents. There is a similarly confusing explanation in the article on Chemical equilibrium. Anybody up for fixing that too? - Anonymous 12 July 2007

Please cite one secondary source that describes "the law of mass action" as being "not generally true." I have never seen it described that way (ever). Describing it that way is a "synthesis of published material". See http://en.wikipedia.org/wiki/Wikipedia:No_original_research, and http://en.wikipedia.org/wiki/WP:SYN. Thus, even if it is true, it doesn't belong. I put forth several references describing LMA, as it is used today (in the Contemporary View section), as a true equilibrium equation. Can you name even one in the last 50 years that concludes it is "not generally true." "If your viewpoint is in the majority, then it should be easy to substantiate it with reference to commonly accepted reference texts." See http://en.wikipedia.org/wiki/WP:NPOV Since this is the "contemporary view", a recent secondary source is called for (lets say, the last quarter century?). - Anonymous 12 July 2007


 * You speak of commonly accepted reference texts, yet you cite only websites. For reliable sources, it is much better to look at books and articles specifically about the LMA, such as some that I have cited above.
 * My impression is that the LMA was originally a kinetic idea, but some people use the name to refer to the definition of the equilibrium constant. I think it is also a cultural divide between different subdisciplines: perhaps general and analytical chemistry textbooks are more likely to use LMA to refer to equilibrium, while physical chemistry books tend to use it for kinetics (or better yet, skip the confusion and not use the name at all). --Itub 10:10, 12 July 2007 (UTC)

New lead-in
I have drafted a new lead-in (below) for discussion here. Please bear in mind that because this subject is so "controversial" a simple one-line lead-in will not do. Constructive comments, please.

The Law of Mass Action was first proposed by Guldberg and Waage in 1864 but was modified in subsequent papers. In its final form (1879) it was suggested that the "chemical affinity", or "chemical force" between a set of reactants in a chemical reaction was proportional to the "active masses" of the reactants, each raised to the power of the stoichiometric coefficient of the reactant in the equation for the reaction. For homogeneous systems active mass is equal to concentration. The final form of the general expression,derived from this, for an equilibrium constant is the same as that used today, apart from activity corrections.

Guldberg and Waage recognised that, at equilibrium, the rates of reaction for the forward and backward reactions must be equal. It was also proposed initially that the rate of reaction was proportional to the product of the concentrations of the reagents involved. This is often used as an alternative statement of the Law of Mass Action and is valid for so-called "elementary" reactions. The later generalisation of the rate expression is not considered to be valid today.


 * Again you are starting with the history before saying what the article is about. The names of the discoverers and the date are not that important for the first sentence of the lead. Why not something like this for the first paragraph:


 * The Law of Mass Action relates the "chemical force" that drives a chemical reaction with the "active masses" of the reactants. It was first proposed by Guldberg and Waage in 1864 but was modified in subsequent papers. In its final form (1879), it suggested that the "chemical affinity", or "chemical force" between a set of reactants in a chemical reaction was proportional to the "active masses" of the reactants, each raised to the power of the stoichiometric coefficient of the reactant in the equation for the reaction. For homogeneous systems active mass is equal to concentration. The final form of the general expression, derived from this, for an equilibrium constant is the same as that used today, apart from activity corrections.


 * However, I anticipate that there will still be objections on the basis of "who decides which is the 'real' law and which is the 'alternative'?" and that the beginning of the lead is phrased in 19th-century language. --Itub 14:32, 12 July 2007 (UTC)

I thought the article was about a bit of chemical history! Never mind. I accept the idea of your suggestion, but I think it needs to be re-worked along the lines that there are two usages for the term LMA, the affinity (equilibrium) useage and the kinetic useage. In my draft I described them in two paragraphs in order to make the distinction clear. Please help me out because I really don't see how this can be encapsulated into a single sentence. The 19th century language was chosen intentionally in order to emphasize the historical nature of the topic. Petergans 15:37, 13 July 2007 (UTC)


 * Recently, an editor at another dispute about a lead said the following "this is very important, the introduction must introduce". This is by far the most important criteria by which introductions must be judged. I believe this proposed lead, with its large number of outdated terms in inverted commas (likely unfamiliar even to a practicing chemist not concerned with history), is not penetrable enough for the layman reader (say a 10th grader/someone with a humanities background). I appreciate that Petergans proposed his change in the talk page rather than the article itself. But in the absence of any relevant definition for the word chemical affinity, the proposed lead does not mean anything. It fails to convey any information, let alone convey it in an accessible way. I think calling the law of chemical equilibrium LMA is a minority view among authors, one we do not need to emphasis needlessly. Lets just say that LMA gives an expression for the rate of reaction, one that is not generally valid, and then uses it to derive an expression for the equilibrium constant, one that is generally valid. This seems to convey all essential information easily. Loom91 19:25, 13 July 2007 (UTC)

Loom91 has consistently failed to understand the nature of this article. It is about a piece of chemical history. The Law of Mass Action has no application in 21st. century chemistry, whether in relation to equilibria or kinetics, since it has been superseded by sounder theories. The derivation of the general equilibrium expression cannot, today, be based on an incorrect kinetic expression. The rate expression for an elementary reaction is just that even if some texts refer to it as the LMA which, to be specific, comes from the 1867 paper (v=k[A][B] ), not the general expression given in the 1879 paper.

One cannot re-write history. If G&W wrote about chemical affinity, then that’s how it has to be reported. The first sentence might read
 * The Law of Mass Action was proposed by Guldberg and Waage in the period 1864-1879 in an effort to quantify the forces that drive a chemical reaction.

It is wrong in principle to state, in the lead-in, that the LMA is not generally valid, even with qualifications. To do so adds unnecessary confusion. If one sticks to the 1867 definition of the rate expression the issue of validity does not arise. The suggestion that the equilibrium aspect of “LMA is a minority view among authors” is a POV, unsubstantiated by any evidence. In any case it is irrelevant to a Wikipedia article which should reflect all aspects of the topic. The fact that 100% of the calculations reported by G&W relate to equilibrium systems has been stated previously in this discussion and is simply ignored by Loom91.

We do not need to be given patronizing homilies about the nature of the lead-in. We have all read wp:lead and have tried in our own ways to follow the guidelines given there. Petergans 08:49, 16 July 2007 (UTC)


 * Your repeated assertion that LMA has no relevance to modern chemistry is not borne out by the facts. The facts clearly say that authors do use the name LMA to refer to the rate law of elementary reactions, and a minority use it to refer to the law of chemical equilibrium. You can not change the reality. This article is about history, but it is not solely about history because a large number of authors do not consider the name LMA to be purely a piece of history. I didn't say that the equilibrium aspect of LMA in G&W's original papers is irrelevant or minority. I said that the use of the name LMA by some authors to refer to the Law of Chemical Equilibrium (which states that the ratio of the activities/concentrations of reactants and products in a reaction is a constant dependent only upon temperature) is a miinority view. Most authors use it to refer to the kinetic expression, as Itub has also pointed out. Loom91 09:32, 16 July 2007 (UTC)


 * I wouldn't claim that the sample of books I found above is representative, but I do agree that both modern usages are common. They are both wrong in my opinion, as I prefer the Atkins approach, but my personal opinion doesn't matter much here. ;-) The websites linked to by our anonymous friend also give plenty of examples where people use it to refer to equilibrium. In reply to Petergans: I think the nature of the article is exactly the point of this discussion. What should the article be about? You think it should be about the history, but I think you would agree that it is a fact that people today use the words "law of mass action" to refer to certain equations, whether they have anything to do with G&W or not. As you say, the article should represent all aspects of the topic, which includes these (arguable) modern misuses as well as the history. --Itub 09:44, 16 July 2007 (UTC)

Actually, I don't agree. As far as I can tell the equations to which people refer were first put forward by G&W. That's why I think this topic is about history. The modern stuff, including misuses, is in the contemporary view section. Petergans 13:18, 16 July 2007 (UTC)


 * The point is that the name LMA is still used, and not only in a historical context. There's an overhwelming amount of reference to support this. Do you contest? Loom91 13:48, 16 July 2007 (UTC)

When the name is used it it has always referred to the law (in one form or another) proposed by G&W. Petergans 20:50, 16 July 2007 (UTC)


 * Yet you insist that the law of mass action is "about" equilibrium, while many recent books say things like "the law of mass action is d[A]/dt = -k[A]". Maybe the original papers were about equilibrium, but the modern use of the term is sometimes completely about kinetics. Some other books say something like "the law of mass action is K=[B]/[A]" and are talking just about equilibrium. I think the best solution is to start the article more or less like this:
 * In chemistry, "law of mass action" can refer to either of two equations/laws/whatever: 1) the definition of the equilibrium constant K = [B]/[A]; 2) the rate equation for an elementary reaction d[A]/dt = -k[A]. Both usages stem from the research by G&W in 1864-1879 on chemical equilibrium and its relation with chemical kinetics."
 * I'm abbreviating, of course, but I hope you can see what I mean. --Itub 07:17, 17 July 2007 (UTC)

This is OK by me. After revision, this would be the complete lead-in.
 * In chemistry, Law of Mass Action has two aspects: 1) the static aspect, concerning the composition of a reaction mixture at equilibrium and 2) the dynamic aspect concerning the rate equations for elementary reactions. Both aspects stem from the research by Guldberg and Waage (1864-1879) in which equilibrium constants were derived by using kinetic data and the rate equation which they had proposed. Guldberg and Waage also recognised that chemical equilibrium is a dynamic process in which rates of reaction for the forward and backward reactions must be equal.

Petergans 08:59, 17 July 2007 (UTC)


 * I was waiting to see if Loom91 or anyone else had any comments, but well... I like your proposed version, as it is written in modern language and makes it clear from the beginning that there are two different aspects to the law. --Itub 10:47, 19 July 2007 (UTC)


 * That's fine with me, but shouldn't the lead also include what these two statements are, instead of only implying that they exist? Loom91 12:51, 19 July 2007 (UTC)

Thank you for the agreement. The lead-in has been replaced. There are no statements of "the law" because 1) G&W changed the statements with each publication and 2) you objected to using the term "chemical affinity" in the lead-in. There is no modern equivalent to this term. Petergans 07:57, 20 July 2007 (UTC)


 * I added two paragraphs to the lead, briefly explaining the contents of the law. Loom91 12:45, 20 July 2007 (UTC)

The last part
I have re-written the article on elementary reactions and transferred some material there. This has allowed the last section to be presented in a more logical fashion. Petergans 10:38, 24 July 2007 (UTC)

What duplicate derivation?
Petergans, what do you mean by duplicate derivation? Loom91 06:37, 27 July 2007 (UTC)


 * What you had written is virtually identical with the derivation in the 1879 section, which I had modified to be explicit in terms of reaction rate. Incidentally, the meaning of the subscript f is not clear. Petergans 08:47, 27 July 2007 (UTC)


 * They are not identical. The 1879 section uses affinity constants and active masses. Simply writing that the affinity constants are rate constants, without writing out what expression is beiing referred to, is confusing. Particularly since the contemporary view is a separate section and some readers may decide to read only that section, without reading the history. Loom91 17:47, 29 July 2007 (UTC)

Law vs. Model
I think we should refer to mass action as a mathematical model. It is rather a simplified version of the chemical master equation that was tractable and is good enough for some cases. But now we are seeing many exceptions and I think it's better to take the more conservative route and refer to mass action as a model, not a law. —Preceding unsigned comment added by Neffk (talk • contribs) 21:09, 25 August 2009 (UTC)

Semiconductor Physics
The law of mass action is very important in semiconductor physics, and although I believe the maths to be exactly the same, the application is quite different. I've added a stub of a section for that, but if someone more knowledgeable than me could extend it, I think that'd be really helpful. —Preceding unsigned comment added by 131.111.8.97 (talk) 14:36, 12 November 2009 (UTC)

Water memory
It is alleged that this law is inconsistent with the concept of water memory.--5.15.23.245 (talk) 23:30, 15 December 2013 (UTC)

Kinetics
Is this law about kinetics, as some recent edits try to imply? As I recall, this law is not about kinetics as one can see in the comtemporary view section. It has been indeed derived kinetically at its formulation by Guldberg and Waage. Then van′t Hoff rediscovered the kinetic rate equation needed in the derivation by GW.--188.27.144.144 (talk) 09:28, 17 December 2013 (UTC)
 * The equivalent pages in french, deutch and spanish clearly state that this law is about thermodynamics. There seems to have been an edit war and the current version is very... confusing Lewisiscrazy (talk) 06:53, 25 January 2018 (UTC)

Serious need of definition
The page, as it is currently written, should be renamed to "Historical Overview of the Law of Mass Action". It's really hard to read this page to get any useful intuition on the subject - a definition was lacking and any explanation was hidden in a lengthy discussion of the articles defining it, more than a hundred years ago. The page should be focused on modern use of the term. I added a definition, which I rephrased from the web (and cited), and I hopefully got it right. I would like someone to go over it and make their suggestion. --Kwikwag (talk) 14:41, 3 September 2015 (UTC)

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reaction rate
I have a question concerning the two excerpts: "The derivation from the reaction rate expressions is no longer considered to be valid."

... and later on....

"In general many reactions occur with the formation of reactive intermediates, and/or through parallel reaction pathways. However, all reactions can be represented as a series of elementary reactions and, if the mechanism is known in detail, the rate equation for each individual step is given by the r_f expression so that the overall rate equation can be derived from the individual steps. When this is done the equilibrium constant is obtained correctly from the rate equations for forward and backward reaction rates."

Isn't this a contradiction? So if I know all reactions, a derivation from the reaction rate expression IS Valid? 89.15.167.48 (talk) 10:42, 19 January 2018 (UTC)

what does "mass action" mean?
Can there be some kind of brief etymology section or at least an explanation of what the name of this article means? The name of this law doesn't make sense to me and I can't find any explanation for why it's called "mass action". There's a definition of something called "active mass" in the middle of the History section of the article (which probably would have been more helpful in the introduction), but then why isn't it just called Law of Active Masses? If this was just an arbitrary naming choice on the part of the people who wrote the original papers, then it would be nice if the article said that somewhere. thanks 64.33.129.250 (talk) 00:56, 2 February 2022 (UTC)