Talk:Gibbs free energy/Archive 1

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Archive 1 Archive 2


Is this a typo:

"by showing that the heat evolved [sic] in a reaction"

which is found under section History, paragraph 5?

Shouldn't it be involved?


'04 questions

In the section that derives Gibb's free energy, an explanation of what Q is, is missing. Perhaps someone who knows exactly what Q is defined as, could edit the page with an explanation.

Q is heat transfer, and the article says so repeatedly. — Miguel 03:21, 2004 Oct 28 (UTC)
Q must be dimensionless for ln(Q) to make sense. I think it is the relative pressure (the ratio between the actual pressure and the atmospheric pressure)
--HenrikMidtiby 21:06, 16 January 2006 (UTC)
Q, if I remember correctly, is the reaction quotient. It is similar to the equilibrium constant expression; they are the same after the reaction has gone to completion. Hope that helps. Gchriss 18:24, 5 February 2006 (UTC)
heat transfer is small "q" --M1ss1ontomars2k4 18:39, 13 May 2006 (UTC)


the identity relating nFE to RTlnK is incorrect (there shouldn't be a minus there)

You're right. It's been changed. --M1ss1ontomars2k4 18:43, 13 May 2006 (UTC)

Isothermal, isobaric processes

The article states "Such processes do not seem to move on a P-V diagram; they do not seem to be dynamic at all." I take issue with this, because I can name a million isothermal, isobaric processes that definitely move on a P-V diagram. Consider boiling water at atmospheric pressure and 100 degrees C... it goes from liquid to gas, and therefore the volume changes drastically. Shall we remove this statement? Ed Sanville 21:54, 10 November 2005 (UTC)

What is it?

What does the G equate to in conceptual terms? Is it for instance, the amount of thermal energy contained in a given volume? Could it be expressed as 'the amount of energy that would dissipate if the mass of given material were released to the great vacuum of space', not considering radioactive decay or chemical interactions? -- Pinbucket 00:06, 18 March 2006 (UTC)

No, basically, if you do an energy balance on constant-temperature, constant-pressure reacting system, i.e. final "total energy" = initial "total energy", you can facilitatively divide this total energy [H] released from the chemical reaction into two parts: (a) useable part = [G]; (b) un-useable part = [TS].--Sadi Carnot 21:05, 11 April 2006 (UTC)
The decrease of the Gibbs free energy equals the maximum non-volume (non-boundary) work a system can perform under isothermal, isobaric conditions. That's not quite the same as the maximum work, which is the decrease in the Helmholtz free energy. As correctly noted above, enthalpy [H] equals [G] plus [TS]. For example, a fuel cell can convert the decreased enthalpy into electrical work, the latter equal to the decrease in [G], with the remainder lost as heat. ----PotomacFever 14:24, 21 June 2006 (UTC)

What is this thing called?

I removed the following:

(sometimes also known as free enthalpy)

I've read dozens of books on thermodynamics, and I've never heard this.--Sadi Carnot 19:18, 25 April 2006 (UTC)

Er...try doing a search on Google. I'm guessing free enthalpy is not a common term where you/I live. --M1ss1ontomars2k4 18:44, 13 May 2006 (UTC)
M1ss, I checked the A to Z dictionary of Thermodynamics (Perrot), it says:
Free enthalpy – A name sometimes given to the Gibbs free energy function, G = H –TS, by people whose mother tongue is not Shakespeare’s language.
Hence, knowing personally in American engineering schools, of which Willard Gibbs was the first, that this term is not used (and only confuses the matter), I will tone down the acknowledgement of this association in the article. --Sadi Carnot 15:19, 15 May 2006 (UTC)

See also following section.

Gibbs free energy to Gibbs energy move debate

First conversation

I had certainly never heard of "free enthalpy" for this parameter before, and it seems to me a poor (confusing) choice of terminology — if it is to be referred to in the text, perhaps "rarely" or "occasionally" is fitting. More importantly, the IUPAC recommendation is that this parameter be called either the Gibbs energy, or the Gibbs energy function — note, no "free"! For this reason, this article should be swapped/changed to the corresponding url/heading. (Note: I have already done this once (see history), and am waiting for Sadi to explain why it shouldn't happen, as he (she?) has reversed that change.) - DIV, 2006-05-31 (Melbourne)

My anonymous friend, first I don't see how you seem to find yourself comfortable jumping into a major article as an unknown editor and so freely making such drastic changes. Secondly, I am a chemical engineer, thermodynamic terms are my specialty, I have read near to all of Willard Gibbs books, and I specifically read about Gibbs free energy. Thirdly, reading thermodynamics books, textbooks, and articles (and physical chemistry books) in general is my hobby; I personally own over 50 such thermodynamics books. Fourthly, regardless of what justification I might or might not have as regarding experience in using this term, it would be clearly obvious from the history sections of Gibbs energy (about five edits going back to ‘05) as compared to Gibbs free energy (about 80 edits going back to ’03) that the later terminology is well preferred over the former. Also, in the future, any time you feel like making such drastic moves of entire articles please put your proposals on the talk page and let them sit for a month or two so to gather up the common opinion. Thank-you:--Sadi Carnot 17:26, 30 May 2006 (UTC)
My friend, please go back and fix all of the many changes you seem to have made in regards to terminology; I don't even know where to begin with the mess of things you have made. You have to understand that when you try to change one term in one article you disrupt the homogeneity of the entire encyclopedia and specifically the set of articles (probably about 50+) that use this term.--Sadi Carnot 17:35, 30 May 2006 (UTC)

To further clarify, please see: Free energy (disambiguation); there are over 30+ editors, not one of whom is myself, who have contributed to this page and you see, of course, what terminology results. Again, please be more careful in the future. As to a loose rank, in regards to their prevalence of use, the following is order is preferred:

  1. Gibbs free energy (most used; unambiguous; preferred in technical papers, used in themal physics book, used in biological thermodynamics books, used in chemical engineering books, used in biochemistry books, used in scientific dictionaries, etc.)
  2. Free energy (used greatly in older books, biological writings, chemistry books, used loosely, etc.)
  3. Gibbs free energy function (used in derivations)
  4. Gibbs energy (used in physical chemistry books)
  5. Thermodynamic potential at constant pressure (term used by Fermi in 1936)
  6. Gibbs energy function
  7. Gibbs function (used in some thermodynamics textbooks)
  8. Free enthalpy (used sparingly in languages other than English)
  9. Free energy function
  10. etc.

I hope this helps. If you wish, you can read an entire history of how the term has changed over the course of time in Raffa’s Drug-Receptor Thermodynamics (textbook) chapter 4: “A Brief History of Thermodynamics Terminology and Notation.” (pgs. 56-59)--Sadi Carnot 17:46, 30 May 2006 (UTC)

Hello Sadi. I respond to a few of your points.
  • I am only slightly more anonymous than you. If it helps the conversation, I am also a Chemical Engineer. From the link on your user account I would rate our education and academic achievements as comparable. Feel free to call me by my initials, DIV. The dispute is not between myself and yourself. The question is whether you feel that your qualifications are superior to the combined authority of those on the relevant IUPAC committee. I would tend to defer to IUPAC. I am also curious whether you have been elected to be an editor?
  • I am well aware that changing content in one location can potentially break many links. This is why I executed a direct swap between Gibbs energy and Gibbs free energy, making the latter the redirect instead of the former. You will notice I didn't do this with Helmholtz energy, because I don't like the trouble of having to log in with an account, so I cannot directly create (new) pages. Also, no doubt I have missed a couple of things, but my time is only finite.
You suggest two reasons for maintaining the status quo. If I quote you very liberally:
  • you note that changing the terminology will involve much work in ensuring all the reliant changes cascade through.
  • you further cite the history of the word, and make some claims about current usage patterns.
To my mind these things are entirely insufficient grounds to refuse moving the article to the IUPAC–recommended heading, and leaving a redirect at this and all other popular headings. IUPAC generally has very good reasons for making their recommendations, and it doesn't help their implementation when a "major article" such as this one uses the incorrect terminology!
There is almost always a huge resistance to change, and when Wikipedia was in its infancy and someone created the "Gibbs free energy" page using one of the very popular terms, it is not at all surprising that searchers for "Gibbs energy" found it there (eventually), and contributors added content there. Also, most users and indeed some contributors are apathetic. Whereas I dislike letting even small errors go uncorrected.
  • I take your point about leaving comments to get some feedback. I must say I was surprised to find the article under the 'wrong' listing, and may have been somewhat impatient to 'fix' it. I was of the opinion that the IUPAC reference I provided (numerous times) would be understood and accepted by any interested party. I am not of a mind to undo any of my changes. I will, however, defer reimplementing changes you have undone.
... Also, I wouldn't necessarily be so sure that your comment on 'free enthalpy' fits the definition given under the previous heading.
Regards, DIV 2006-06-01 (Melbourne)
First let me say my prejudice is towards "Gibbs Free Energy". But I totally agree that IUPAC terminology is the Wikipedia standard and we should conform to its terminology. As far as I can determine, "Gibbs Energy" is the IUPAC term for what I would normally call the Gibbs Free Energy. So the bottom line is that I support the idea of changing all references to Gibbs Free Energy to Gibbs Energy. But this must be done in a slow, coordinated manner, preferably by non-anonymous editors who are familiar with the thermo articles. I would be glad to start the process on those article that I am familiar with, once a consensus is reached. PAR 20:40, 31 May 2006 (UTC)
Hi PAR, thanks for your input.
I wanted to summarise two further arguments for the case of moving to "Gibbs energy" as the main listing:
  • As time passes, (unless the IUPAC recommendation changes) more and more people will come to be familiar with "Gibbs energy" rather than "Gibbs free energy". Sadi referred to a library of 'classic' texts. I contend that current and forthcoming texts will increasingly use the term "Gibbs energy". A good example is the standard work by Stan Sandler, Chemical, Biochemical, and Engineering Thermodynamics, where you will see the index makes no mention of "free energy" (although a cross-reference could have been useful, I admit). Professor Sandler, editor of the AIChE Journal, is an expert in the field (see 1, 2, 3) you would expect. What I am trying to say is that the change will happen, and it is better for it to happen now.
Another example of the same usage is the latest edition of Perry's Chemical Engineers' Handbook, in the section by van Ness & Abbott.
—DIV, Melbourne ( 06:26, 2 June 2006 (UTC))
  • The fact that no-one made the change until now may be attributed to many causes. I have already mentioned apathy. Another is that changes can take a while to build up 'momentum' and propagate. But finally, with all due respect, a lot of the people looking at this page will emphatically _not_ be experts on thermodynamics. When I use Wikipedia, it is generally to look up things I do not know a great deal about. {I forget why exactly I viewed "Gibbs (free) energy" on this occasion, but it was related to the title of a paper I was trying to check up on (in French), which contained the phrase "chaleurs de réaction".}
Regards, DIV - Melbourne (2006-06-01)

Second conversation

DIV, I happen to be coincidently reading Baierlein’s 2003 Thermal Physics (textbook) and in chapter 10 “The Free Energies”, section 10.4, the topic is Gibbs free energy. Imaging that! Maybe they didn’t get that 1988 IUPAC memo? The point here is that this is an article for the English speaking world, we have to go with the most common term, i.e. the one that is most commonly used in textbooks, lectures, and in the common tongue. Maybe, in the future, things will change and the majority will start to use IUPAC standards?

Coincidently, off Amazon this last month I ordered over 30 new thermodynamic books (Sandlers I bought years ago), from virtually every branch of thermodynamics, you name it and I probably ordered it (or have it). My point is that I am going to reason that I am familiar with what is commonly used. To clarify this discussion one last time, the chapter “History of Thermodynamic Terminology and Notation”, in the book Drug-Receptor Thermodynamics, we find:

“Two conveniently defined functions are those that were originally described by using the word ‘free’ to indicate that under special conditions these were energies that were ‘free’ or available for work. In modern terms we use Gibbs energy or Gibbs function and Helmholtz energy or Helmholtz function; the descriptive ‘free’ has been banished (Mills et al. 1988), although it unfortunately continues to be used.” [(1)Mills I, Cvitas T, Homann K, et al. (1988). Quantities, Units and Symbols in Physical Chemsitry, IUPAC, Blackwell Scientific Publications, Oxford.; (2)Raffa, R.B. (2001). Drug-Receptor Thermodynamics: Introduction and Application. New York: John Wiley & Sons, Ltd.]

Strange, the descriptive 'free' was banished over 20 years ago? Maybe the people who started this article in 2003 weren't aware of the banishment? Now, here are the stats for Google hits:

for the term “Gibbs free energy”:
Results 1 - 10 of about 2,310,000 for Gibbs free energy [definition]. (0.19 seconds)
for the term “Gibbs energy”:
Results 1 - 10 of about 3,680,000 for Gibbs energy. (0.17 seconds)

As we see there is a toss-up. Yet when it is referenced in scientific encyclopedias we find a common standard. For example, here is the article as found in Eric Weissteins World of Physics: Gibbs Free Energy. The same is true for Britannica, here is a 2002 reprint of their section on free energy:

In thermodynamics, energylike property or state function of a system in thermodynamic equilibrium—it has the dimensions of energy and its value is determined by the state of the system and not by its history—expressed in two forms: the Helmholtz free energy, A, sometimes called work function, and the Gibbs free energy, G, sometimes F. If E is the internal energy of the system, PV the pressure–volume product, and TS the temperature–entropy product, then A = E - TS and G = E + PV - TS. Free energy is an extensive property; i.e., the magnitude depends on the amount of the substance present in a given thermodynamic state.
The changes in free energy, ΔA or ΔG, are useful in evaluating certain thermodynamic processes. In a reversible process, the work under constant temperature and constant volume is equal to the change in the Helmholtz free energy, ΔA, and the work under constant temperature and constant pressure is equal to the change in the Gibbs free energy, ΔG.
Changes in free energy can be used to judge whether certain transformations of state can occur spontaneously. Under certain conditions of constant temperature and volume, the transformation of state will occur spontaneously, slowly or rapidly, if the Helmholtz free energy of the final state is smaller than that of the initial state; that is, if the difference ΔA between the final and the initial state is negative. Under conditions of constant temperature and pressure, the transformation of state will occur if the change in the Gibbs free energy, ΔG, is negative.

We can go on and on but the fact remains that when people write up the entry in the encyclopedias (as the above two) exacting clarification is used along with a tendency to use the most informative and common term. In wikipedia, we have 120+ links to the Gibbs free energy page and 0 links to the Gibbs energy page. I would assume the 120 people who made these links didn’t get the 1988 IUPAC memo either? It is one thing for small committee of chemists to supposedly "ban" a term, and quite another for the world to want the term banned. As we see, we are in the middle of a 100+ year terminology evolution or transformation window, since the concept was developed by Gibbs in 1876. In time, maybe another 100 years, we will naturally (hopefully) gravitate towards a final agreement. To solidify my point, I have added 7 external links to the article (as shown below) --Sadi Carnot 02:56, 20 June 2006 (UTC)

Third conversation

Sadi, I have to acknowledge that you are clearly someone who has spent a considerable amount of time and money ordering books. You are also evidently someone who enjoys sharing their knowledge, and demonstrating your mastery of the topic. Unfortunately your personal interest in the historical development of this term may be clouding your judgement. Indeed, Wikipedia's articles are supposed to be free of personal opinion, yet somehow a section titled "Why is 'free' so important?" appeared prominently in the body of the article itself (rather than this Talk page) shortly after our first conversation. And the IUPAC definition was somehow relegated to the last reference! While I refrained from making any further alterations to the article until a consensus was reached on the discussion pages, it is disappointing that you did not similarly restrain yourself. As with our first conversation, your arguments to retain the word 'free' in the article title are not persuasive:

  • You write, with what I presume to be sarcasm, "Maybe [those authors] didn’t get that 1988 IUPAC memo?" Well, maybe indeed! It is a sad truth that many authors and editors do not confirm that they are using standard (IUPAC, SI, ...) terminology. Some others may have a personal view that standards are not important, provided people 'know what they're talking about'.
  • You have quoted Raffa's statement that the word 'free' was "banished" some 20 years ago. Yet for some reason you defer instead to the unknown authors who first set up the name of this page! There is certainly some inconsistency here, as previously you seemed averse to the submissions of "anonymous" contributors. Until shown otherwise, there is no inherent reason to believe that the original creators and contributors were in any way experts on thermodynamics in general or Gibbs energy in particular. (Of course, it is easy to make 'motherhood statements' such as these without following up: I assure you that I have viewed the history page for the article and followed up several of the early contributors. A couple of them had science degrees, but none indicated a relevant specialisation.) As a further example, perhaps you would care to turn your sarcasm to the August 2005 creator of Standard Gibbs free energy change of formation (see Merge, below). "Perhaps he didn't recognise the authoritative 'Gibbs free energy' article?"
  • If you want to trust generalist encycopædias (e.g. Brittanica) over world–recognised experts (e.g. Sandler), then that is your prerogative. However, for the sake of web–users everywhere, please do not impose that on others. A work such as Brittanica is an excellent general source of information. This does not mean that it is entirely up to date. Not every article is updated each edition, and those for which the definition is not obviously wrong won't be changed. I would be curious to learn which references (if any) the Brittanica article cites, and in what year they were written. As should be self–evident by now, changes in standards can take some time to cascade through the literature. (Those authors of Brittanica articles can probably more aptly be characterised as summarising the literature, rather than producing new knowledge.)
  • Finally, you refer to the numerous links to the article listed at 'Gibbs free energy'. This, too, proves precisely nothing. I put it to you that the creators of those links took it on faith that this page was in the correct location. It is not their business to shift pages around that they are not expert in. By way of example, the Gibbs energy article itself links to:
  • Thermodynamic entropy ...this might be considered a non-systematic entry, perhaps "Entropy (thermodynamics)" would be better? But normally someone working on the Gibbs energy article isn't going to bother to get involved in questioning or changing that. (Of course, this is a less significant change, and is still within the realm of thermodynamics.)
  • Rule of thumb ...this has essentially nothing to do with Gibbs energy, or even thermodynamics in general. So it is an excellent example of one of the many, many links made to Wikipedia articles by people who are not expert in the content of those (target) articles. Perhaps "Rule of thumb" should be changed to or merged under "heuristics"? Maybe not! I don't know enough to make this decision, and so I would simply create a link to the existing site. Just like the people who linked to 'Gibbs free energy'.

In summary: you have not abided by PAR's sensible call (see above) to establish a consensus prior to a slow, systematic process of amendment; you have raised a few more points that are not persuasive; and after almost 7 months you have not found any supporters of your view. Given that the consensus view is for the IUPAC standard terminology 'Gibbs energy' to prevail (DIV + PAR = 2), rather than the traditional 'Gibbs energy' (Sadi = 1), you can await the imminent moving of this article.

— DIV (Melbourne) 08:38, 26 December 2006 (UTC)

DIV, the 2004 Oxford Dictionary of Chemistry defines G as “Gibbs free energy”, the 2006 Encarta encyclopedia defines G as “Gibbs free energy”, Britannica defines G as “Gibbs free energy”, Barnes & Noble’s The Essential Dictionary of Science defines G as “Gibbs free energy”, the 2004 McGraw-Hill Concise Encyclopedia of Chemistry defines G as “Gibbs free energy”. The rule in Wikipedia is to list an article using its most common usage. I really don’t know where you’re going with this converstion? --Sadi Carnot 22:52, 27 December 2006 (UTC)
Another obvious point, is that Gibbs free energy is not exclusively a topic in “chemistry”, it is a topic in physics, thermal physics, chemical physics, medicine, thermoeconomics, chemical engineering, and many others. Thus, IUPAC is not the governing standard for encyclopedias, which are written for the lay person, not the chemist. --Sadi Carnot 23:28, 27 December 2006 (UTC)
As a graduate student in physics, I felt I should voice my opinion briefly here. I agree with Sadi on this point. All physics professors I have spoken to about this topic and all physics textbooks I have read on this topic use the term Gibbs free energy. It is thus my impression that, while chemists and the IUPAC may prefer Gibbs energy, physicists show no signs of abandoning the term Gibbs free energy, and the term Gibbs free energy seems to be wider spread otherwise as well. Thus I vote for keeping the name Gibbs free energy. Silroquen 20:38, 29 December 2006 (UTC)

I just want to put in the request that if this move goes forward, there is at least some vestige of the term "free energy" in the form of re-direct or disambig pages. In my experience as a particle physicist, "free energy" is used pretty frequently. In that context, it usually refers to Helmholtz FE and we make little use of Gibbs FE so we don't even use those labels. So it would be useful to not eradicate every instance of the phrase, free energy. I also want to reiterate Sadi's point that free energy(both Gibbs and Helmholtz) are concepts used outside of chemistry and so we do not have to agree with all of chemistry's conventions. -Joshua Davis 23:46, 27 December 2006 (UTC)

I would vote for using the IUPAC designation. I estimate very roughly, from searching google, google books, google scholar, and amazon, that about 30% of recent books and publications use "Gibbs Energy" rather than "Gibbs free energy". It is still a minority, but I believe it is increasing, and some people do care about international standards. It will probably take a few more decades before the new term becomes nearly-universally adopted, but I would rather do it earlier than later. In questions of nomenclature we can always argue endlessly about the pros and cons, but I tend to go for the easier solution of deferring to an established authority, in this case, IUPAC. Of course, there are extremes: if there is a IUPAC proposal that only 1% of the people follow, it's probably best not to use it for now. But 30% use + IUPAC backing is more than enough for me.
Whatever the decision about the title of the article, I don't have such a strong opinion (also, I note that often we use common names for titles of articles about chemicals, rather than IUPAC names). But I do have a strong opinion that the IUPAC-endorsed term should be mentioned in the very first paragraph in the article, rather than near the end, and that whatever mention is made about the "conflict" should include a reference to the IUPAC publication that proposes the term "Gibbs energy", rather than just referencing a random thermodynamics textbook. In the body of the article, the two version of the name could be used interchangeably, as they are already (I don't know if as a result of this conflict, carelessness, or indifference). I expect that most readers wouldn't mind, given that the terms are synonyms. Itub 23:56, 27 December 2006 (UTC)
Itub, all good points; however, I made the same mistake above of doing Google search results for each term, where I found that 38% usage for Gibbs free energy. What I realized, later, was that a three term search always pulls up fewer hits than a two term search, a factor which thus biases the results. --Sadi Carnot 00:34, 28 December 2006 (UTC)
I support to retain free energy term for following reasons.
  1. article was first created with this term.
  2. the term “free” in “free energy” has historical significance.
  3. It is not wrong to use this term.
  4. IUPAC is not strict on using latest term. On their own web-site I found 72 article using "Gibss Free Energy" at least one of them was published in 2004.
However, I appreciate the point raised by user:DIV that people should be encouraged to use IUPAC term. I recommend to include some text in the article to that effect. Also a redirect without free energy term should be provided (I guess it is already there) so authors of other articles using IUPAC definition need not worry about it. If sufficient number of such references builds up this debate can be reopened. pruthvi 00:30, 28 December 2006 (UTC)

I see my name has been used here so I would like to clarify a few points:

  • When I said that Wikipedia recommends IUPAC notation I was not completely correct. To quote Wikipedia:Naming conventions, the "policy in a nutshell" is this:

Generally, article naming should give priority to what the majority of English speakers would most easily recognize, with a reasonable minimum of ambiguity, while at the same time making linking to those articles easy and second nature.

To be more specific, quoting Wikipedia:Naming_conventions (chemistry)

Even with the best will in the world, no set of guidelines can cover every case. Some articles on Wikipedia have non-standard titles through consensus that this is the most commonly used name (in scientific circumstances) for the compound concerned, whatever IUPAC or the other rules suggest... Please do not get into revert wars over the naming of an article: the best place for discussion is on the article's talk page or (failing that) at Wikipedia talk:WikiProject Chemicals

  • With regard to IUPAC it is undeniable that the recommendation is "Gibbs energy" and "Helmholtz energy". To quote the IUPAC Gold Book:

Gibbs energy (function): Enthalpy minus the product of thermodynamic temperature and entropy. It was formerly called free energy or free enthalpy.

  • As to my personal beliefs - I am most familiar and comfortable with the term "Gibbs free energy" but I make a point of not concerning myself too much with terminology, trying to be as adaptable as possible to change, since terminology is a matter of communication, not a matter of fact. If "Gibbs energy" is the wave of the future, and I get the feeling it is, then so be it. HOWEVER, as far as deciding what a Wikipedia article should be named, I think the proper thing to do is to follow the guideline above and find the consensus of the members of the appropriate projects, namely Wikipedia talk:WikiProject Chemistry and Wikipedia talk:WikiProject Physics.

PAR 03:37, 28 December 2006 (UTC)


A Request for comment has been made concerning the title of this article here, cross-posted to WikiProject Chemistry and WikiProject Physics. Physchim62 (talk) 23:58, 28 December 2006 (UTC)

Yet another view on the article name

I support keeping 'Gibbs free energy' as the name of the article rather than 'Gibbs energy'. The comments given above seem to be very thorough on both sides of the argument. I note that the large section [1] provides ample ventilation of the naming issue. The only thing that might potentially be added are references to published debates in scientific journals about which term is better. EdJohnston 18:40, 28 December 2006 (UTC)

The question of naming always raises more dust than light. My own view is that Gibbs energy should be used, following IUPAC unless clear authoritive sources from a standards organisation that covers disciplines other than chemistry that uses the term Gibbs free energy can be cited. I do not think historical useage is in any way important in deciding the name of the article, although it should be mentioned in the article. I agree with Itub that if free energy remains as the title, the IUPAC name should be in the first paragraph. Whatever is decided, the other should be a redirect. There should not be a discussion of the name in the article itself. --Bduke 20:57, 28 December 2006 (UTC)

I hope DIV doesn't mind me changing his/her reference: as the official IUPAC publications are available on the web, it seems sensible to refer to them directly. The term "Gibbs energy" was also used in the first edition of the Green Book (1988). The relevant IUPAP recommendation is Cohen, E. R. (1987). "Symbols, Units, Nomenclature and Fundamental Constants in Physics (1987 Revision), Document IUPAP-25 (IUPAP–SUNAMCO 87–1)". Physica A. 146: 1–68.  Unknown parameter |coauthors= ignored (|author= suggested) (help) which, unfortuantely, I don't have access to (see here for details of paying access, which might be available from university connections). ISO 31-8 might also be relevant. Otherwise, a couple of points which editors might like to consider:

  • The title "Gibbs free energy" is not ambiguous in English. However it causes problems when translated directly in French, where energie libre can only refer to the Helmholz (free) energy. This may be reason for the change in internationally recommended nomenclature.
  • The Gibbs (free) energy is the maximum amount of non-pV work which can be extracted from a closed system, and this maximum can only be attained in a completely reversible process. This important (IMHO) point which is somewhat lost in the current version of the article (I'm sure it wasn't lost on Helmholz!)

Physchim62 (talk) 01:33, 29 December 2006 (UTC)

Outsider comment on name discussion

Someone is requesting outside comments on this debate, and here's mine. Many concepts are known by more than one name. You're never going to settle which name is best. The first sentence of the article can mention the 2 or 3 most common names, and futher discussion of various names, abstracted from your lengthy debate, can be written up as a section. I didn't read too much of your debate, but it seems like there is some concern over breaking links. The is very simple to deal with using redirects (although eventually these should be cleaned up). My bottom line opinion is that if you can agree on 2 or 3 versions of the name to stick in the first sentence, who cares what the real name of the article is? ike9898 22:27, 1 January 2007 (UTC)

It seems to me that that IUPAC tells chemists what to call it, but there is far from any consensus in other disciplines. I suggest that the most likely compromise is to call the article "Gibbs free energy", have a redirect from "Gibbs energy", and mention the latter as the IUPAC recommendation in the lead of the article. Can everyone live with this? --Bduke 23:18, 1 January 2007 (UTC)
Yes, I agree with this. --Sadi Carnot 00:25, 2 January 2007 (UTC)
I could live with that too. Itub 14:55, 2 January 2007 (UTC)
Having quickly read through the comments here, this seems sensible to me. I care less about page titles than that readers get something useful when they search. Tom Harrison Talk 21:43, 2 January 2007 (UTC)
Thanks for everyone's opinion, I have changed the intros of both Gibbs free energy and Helmholtz free energy to reflect this view (the redirects already exist). --Sadi Carnot 22:23, 2 January 2007 (UTC)
I'd still like to see what the corresponding advice was on the physics side: Cohen, E. R.; Giacomo, P. (1987). "Symbols, Units, Nomenclature and Fundamental Constants in Physics (1987 Revision), Document IUPAP-25 (IUPAP–SUNAMCO 87–1)". Physica A 146: 1–68, as mentioned by User:Physchim62 in the section above. This work is safely locked behind pay walls, so someone will have to go to the library to consult it. If they agree with the chemists, I'd be more inclined to switch to the name 'Gibbs energy'. EdJohnston 23:26, 1 January 2007 (UTC)
As to physics consensus, I have copies of Schroeder's 2000 Thermal Physics, Baierlein's 2003 Thermal Physics, and Chang Lee's 2004 Thermal Physics - Entropy and Free Energies, and they all use Gibbs free energy and Helmholtz free energy. Not only that they also discuss the Landau free energy, the Landau-Ginnzburg free energy, the minimum free energy principle, the Grand free energy, thermodynamic free energy, and others. --Sadi Carnot 00:25, 2 January 2007 (UTC)
The recommendation published in Physica A, 146, p. 31 is "Gibbs function" (and "Helmholtz function"). It also includes names in French: "fonction de Gibbs" and "enthalpie libre" (but there is no "free enthalpy" in English); and for Helmholtz, "fonction de Helmholtz" and "énergie libre" (but again, no "free energy" in English). Itub 14:55, 2 January 2007 (UTC)

DIV's contributions

Has anyone, other than myself, noticed that DIV is going around Wikipedia and removing all the incidences of the term "free", so far to about 30 articles, with no avail (see: DIV's contributions ), even though there is no consensus and the issue is far from agreed upon? --Sadi Carnot 00:46, 2 January 2007 (UTC)

Thanks to User:Physchim62 for fixing this problem! --Sadi Carnot 22:24, 2 January 2007 (UTC)


Including myself, that’s 10 people, i.e. PAR, Silroquen (keep), Joshua Davis, pruthvi (keep), EdJohnston (keep), Bduke, Itub, Tom harrison, and Physchim62, who vote essentially to keep the two pages at Gibbs free energy and Helmholtz free energy, but to mention the IUPAC and the physics community recommendations in the intro paragraph. I have done this. I hope that this wraps things up. Thanks for everyone's opinion. -Smiley.svg-Sadi Carnot 22:51, 2 January 2007 (UTC)

Until the usage changes and people call them Gibbs energy and Helmholtz energy more than they call them Gibbs free energy and Helmholtz free energy, or until the usage is closer to equal than it is now, I think that the articles should remain where they are. The usage of both seems to be overwhelmingly with "free" included, so I think that the "most common usage" naming convention outweighs the IUPAC recommendation. If the other names catch on, perhaps the articles will be moved in the future.
If there is still disagreement over the naming, I suggest that a formal move request be made. Make sure that you follow all of the directions given on the requested moves page. Many people forget, or do not read, the part about putting a notice at the top of the talk page and/or the part about making a place for discussion and polling. -- Kjkolb 01:58, 3 January 2007 (UTC)
Yes, thank you Kjkolb. User DIV originally moved the pages, without posting notice, several months ago (an action which was reverted). But I think we have consensus now. Thanks for the input. --Sadi Carnot 04:03, 3 January 2007 (UTC)

Thank you for asking my opinion in this matter. I studied chemistry and chemical engineering for my education in the 1970s and early 1980s and I took a number of courses on thermodynamics, which I learned as well or better than most aspects of chemical engineering. Anytime Gibbs free energy was mentioned, it was always called Gibbs free energy. Helmholtz free energy was similarly called that, although was only mentioned a couple times. It was never explained (that I can remember) and I neved bothered to question why the word "free" was used; I just assumed that Gibbs free energy (and Helmholtz free energy) were the correct terms to use.

Afterwards when I went to work in industry, I concerned myself with more practical aspects of plant engineering such as plant equipment, operations, and testing, pumps, valves, chemical analysis, writing operating procedures and tests, and evaluation of non-thermodynamic data. Mention of Gibbs (or Helmholtz) free energy or Gibbs (or Helmholtz) energy almost never came up. Up to this point, I cannot remember anybody calling those quantities simply Gibbs energy or Helmholtz energy in any authoritative way.

I never heard of any mention of any kind of either Gibbs or Helmhotz non-free energy, and I suspect there are no such quantities. I can imagine that Gibbs and Helmholtz were scientists (or engineers) who referred to their newly described quantities as "free energy" in some papers (perhaps for lack of any better term) and subsequent references to these quantities referred to them as Gibbs free energy or Helmholtz free energy respectively, to specify or cite which quantities were discussed.

I have become used to the terms Gibbs and Helmholtz free energies, and I suppose I prefer to have the respective articles named that way. However, if IUPAC, the official chemistry-naming organization of the world, established official names for Gibbs energy and Helmholtz energy, I am willing to go along with that. These concepts are most purely chemistry concepts, and the non-chemistry world should follow the lead of this chemistry organization, just like fundamental physics organizations define Systeme International units of distance, time, etc. for everybody. In either case of course, the alternate names should be cited at the start of the article as is customary in Wikipedia and similar encyclopedias, and REDIRECTs should be made for the alternate names.

There have been similar controversies regarding naming of articles such as "Gasoline" and "Petrol", and IUPAC and common names for chemicals such as ethanoic/acetic acid. It's not that big a deal with the REDIRECTs and it can go either way. Perhaps a compromise in the text in other articles might be to say "Gibbs (free) energy". H Padleckas 03:02, 4 January 2007 (UTC)

I'm glad to see that consensus has been reached and just wanted to chime in (albeit a little late!) in support of Gibbs Free Energy as well. As a student of Organic Chemistry, General Chemistry, Physics, and in preperation for the MCAT, the term Gibbs Free Energy is used exclusively. Just thought it might be relevent to point out what is being taught in American Higher Education.--Robert Stone, Jr. 03:24, 5 January 2007 (UTC)
I am very much inclined to concur with your (Sadi's) opinion, I know these terms as Gibbs Free Energy and Helmholz Free Energy. I guess we are not thát strict about following IUPAC, we follow the name that the most people know, and when that gets close to 50-50, we follow IUPAC. As such, I would vote against renaming the articles. That said, the reason for the word 'free' in the terms, should be made very clear in these articles. Hope that you, as one of the founders of thermodynamics, are able to do that ;-). I'll have a look as well later. --Dirk Beetstra T C 18:41, 4 January 2007 (UTC)
Hmm...I guess I missed something while I was on holidays. I'm rather inclined to keep the word "free". For the record, generally speaking, external resources should not be interpreted as prescriptive but rather descriptive - I'm happy to see the very beginning of the article mentioning the subtlety, which is more than adequate for this article. --HappyCamper 04:34, 7 January 2007 (UTC)
Thanks for your show of support Happy Camper. Interestingly, this week I'm presently digging up the historical details and typing up the related table of the contributors in the development of molecular orbital theory and I find it curious that Max Planck used the prescriptive “free” as originated by Helmholtz (who he played music with weekly) in his famous 1900 quantum theory paper, i.e. energy "free to be converted into work". --Sadi Carnot 04:58, 7 January 2007 (UTC)
Sorry if I am late to the debate (I was away on holiday), but I also agree with keeping free in the title. If the new IUPAC recommendation sticks and starts making its way into the texts and journals then perhaps we should switch. But I support for now keeping the most commonly used and understood name with an explanation of the IUPAC name in the first paragraph. Biomedeng 14:25, 10 January 2007 (UTC)

I am happy about the consensus that we have reached for now, but I would point out that, as far as I can see, all text books on Physical Chemistry use Gibbs energy as per IUPAC and appear to have done so for 10 years. I have 4 texts such texts on my shelves. The earliest are Atkins (4th Ed, 1994) and Laidler and Meiser (2nd Ed, 1995). I supported the consensus because disciplines other than chemistry are not following IUPAC. Chemistry is solid behind IUPAC in how it is currently taught. We may have to look again at this in a couple of years. --Bduke 23:49, 10 January 2007 (UTC)

Yep, Atkins has always been very meticulous about following the latest standards, in my opinion. Other textbooks might not, especially the more "applied" ones. I imagine that if you look at a textbook called "Physical chemistry for ..." it might be more likely to use the older or non-IUPAC conventions. Itub 23:57, 10 January 2007 (UTC)
I hate to resurrect this conversation yet again, but the debate does sound interesting. As an undergraduate - and not in chemistry, I might add - I'd venture the opinion that I'm the sort of person these articles should be written for. In my limited experience I've only ever seen Gibbs Free Energy as the term used. According to IUPAC it's incorrect, which makes a kind of sense, because the epithet 'free' is possibly unscientific and unnecessary when it's clearly defined what a Gibbs Energy is. However, most of the scientific world has failed to catch up with this.

I don't believe wikipedia should be an activist system; popular consensus remains with "Free", but as IUPAC are the universally recognised arbitrators of such matters, their word is law. With this in mind I'd suggest a redirect from Gibbs Free Energy to Gibbs Energy, and add a note at the very top of the page indicating that this is now the correct term. The redirect accounts for people searching and including the 'free' term, as that's what they're used to. Sojourner001 16:53, 17 January 2007 (UTC)

Though I would not want to restart the whole debate, I complete agree with Sojourner001, I will not accept any of my students ever using the term "Gibbs free energy". I am not entirely sure why a re-direct from "Gibbs free energy" to the IUPAC recommended "Gibbs energy" should not be put in place! By doing that, users of the old terminology will be educated by wikipedia and IUPAC recommendations will actually end up being followed more quickly by everyone - not just by those who bother to figure out what this term really means. I'd like to end with a quotation from my (very strict) thermodynamics teacher: "There is no such thing as free energy, just ask taxi-drivers and housewives!" Buurma 17:00, 20 January 2007 (GMT)

Why is the attachment ‘free’ so important?

Answer, from Baierlein’s 2003 Thermal Physics (pg. 235), “The change in F (or G) determines the amount of energy ‘free’ for work under the given conditions. The German physicist and physiologist Hermann von Helmholtz had in mind this property when he coined the phrase ‘free energy’ for E – TS in 1882.” I will add this to the article. --Sadi Carnot 04:12, 20 June 2006 (UTC)

That's a great reference, using Baierlein, only I would differ slightly in that the statement can't be applied to Gibbs free energy without adding the qualification that it is the energy free for non-volume work. See, for example, Reiss, Methods of Thermodynamics, pp. 78-79. ----PotomacFever 14:29, 21 June 2006 (UTC)
Thanks for the input, I just added a big history section where I included your suggestion.--Sadi Carnot 05:50, 9 July 2006 (UTC)
I have amended the title from the non–neutral "Why is the attachment ‘free’ so important?" to the more appropriate "Is the attachment ‘free’ so important?" so that it conforms to the Wikipedia guidelines. (Second time I've had to make this type of correction.) I will not repeat here my comments on following the IUPAC definition (see debate, above).
However, it is appropriate here to contrast the retention of word describing the quantity's application with the names of other physical quantities:
  • "Avogadro's carbon number" ...because the number is defined with respect to carbon! (Or see Avogadro's number?)
...actually, shouldn't this really be the "Loschmidt gas number", deferring to historical development?! (Cf. Loschmidt number?)
  • "Reynolds flow number" ...because otherwise we might forget what Re is used for! (Or see Reynolds number?)
  • "Poisson's ratio of transverse to axial strain" ...because it could be catastrophic to get these the wrong way around! (As if we used Poisson's ratio?)
  • The "Péclet Brownian motion number" ...because it is commonly used to assess the relative importance of Brownian motion! This is a compromise, because it isn't clear whether the full name should be the "Péclet Brownian pollen motion number" or the "Péclet Brownian dust motion number" (Ref.). (Perhaps some people even call it Péclet number?)
Well, there are just so many examples that I think I've made my point.
DIV, Melbourne 09:13, 26 December 2006 (UTC)
DIV, these are poor examples. Of course “Avogadro’s carbon number” isn’t used any more, the 2004 Oxford Dictionary of Chemistry lists it as Avogadro's constant (primary) as well as Avogadro's number (secondary). On the other had, as mentioned above, the same dictionary lists Gibbs free energy (primary) and Gibbs function (secondary), but does not list the term “Gibbs energy” at all. I hope the point is clarified. --Sadi Carnot 23:38, 27 December 2006 (UTC)

Gibbs Free Energy, Life Processes and 'Wealth' creation

I'd like to ask a question, or so, here. First, is the relationship of Gibbs' free energy to life processes seems self evident. (Yes?) Next, life forms are highly ordered (low entropy) aggregations of matter. Their formation, therefore, I presume, occurs as another process 'externalises' these, localised, reversals of entopy increase, and of Free Energy decrease. (Is that so?) Also, have, for example, any measurements of photosynthesis, animal metabolism, etc?, ever been quantified to demontrate the fidelity of these life processes to the Gibbs'(etc) thermodynamic equations. (yes or no?) One final point, I've pondered whether the (human) 'wealth creation' processes could be described by the following word equation:

   Raw Materials + Energy --> Wealth + Pollution

Any comments on this proposition? Thanks! John Courtneidge (presently in Toronto, Canada)

Yes, many people have stabbed in this direction. The first was Herbert Spencer in his 1880 book First Principles, but he only speaks in terms ‘available energy’ and resources, dissipation, evolution, etc., not necessarily free energy as it is in the article. In 1922, Frederick Soddy applied steam engine theory to human life; he states: “life derives the whole of its physical energy or power not from anything self-contained in living matter, but solely from the inanimate world. It is dependent for all necessities of its physical continuance upon the principles of the steam engine. The principles of ethics of all human conventions must not run counter to those thermodynamics.” In 1926, in his book The Biosphere, Vladimir Vernadsky states: “Living matter, as a whole, is a unique system which accumulates chemical free energy G in the biosphere by the transformation of solar radiation.”
You might also want to check out Erwin Schrodingers 1944 book What is Life?, his book is the most referenced book in regards to free energy, entropy, negentropy, solar energy input, and evolution. Another good one is the 1998 book Thermodynamic Theory of the Evolution of Living Beings by Russian physical chemist Georgi Gladyshev. Also, on the back cover of the 2003 book Information Theory and Evolution by theoretical physicist and chemist John Avery we are told that the paradox between the complexity produced by living systems and the seeming contraction between the second law of thermodynamics has its resolution in the Gibbs free energy that enters the biosphere from outside sources. This is just quick list. I hope this helps. Adios:--Sadi Carnot 06:29, 9 July 2006 (UTC)
OK, it being nearly six months on, I'm going to try to do this - I hope many will weigh in with improvements. Best, john John courtneidge 16:55, 23 December 2006 (UTC)
Hi John, first I commented to your query on your "new" talk page. Second, your present contribution is a good topic, however, it will no doubt get reverted by another user fairly soon for a number of reasons, namely we can’t use unsubstantiated theories (every sentence has to be established knowledge); so I will move it here; so we can discuss your contribution, references, and ideas further on that talk page. Thanks: --Sadi Carnot 20:48, 23 December 2006 (UTC)

Conceptual understanding of Gibbs free energy

Moved here from User Talk:Sadi Carnot

Hi, I was looking in the discussion section of the Gibbs free energy page and noticed that you've read a serious amount of textbooks on thermodynamics. At the moment I'm really struggling to conceptually understanding what Gibbs free energy is. I have a couple of chemical thermodynamics textbooks (because I'm studying chemical engineering) but they seem to just define Gibbs without giving a detailed explanation of what it is. So I was wondering if you could recommend a thermo. textbook that gives a seriously detailed description of Gibbs, written in such a way that the simpleton (myself) can understand it.

I have this theory that nothing is beyond anyone, it just needs to be explained in such a way that makes it comprehensible. Is this applicable with thermodynamics or do you think that I'm wasting my time trying to understand it?

Thanks for your time, really appreciate it :)

Lochnagar (07/29/06)



Good question. Gibbs free energy is my favorite topic. As to being able to conceptually understand what Gibbs free energy is; essentially, it is a more advanced and accurate replacement for the term “affinity” used by chemists, of olden days, to describe the “force” that caused chemical reactions. The term dates back to at least the time of Albertus Magnus in 1250.

From the 1998 textbook Modern Thermodynamics by Nobelist and chemical engineering professor Ilya Prigogine’s we find: “as motion was explained by the Newtonian concept of force, chemists wanted a similar concept of ‘driving force’ for chemical change? Why do chemical reactions occur, and why do they stop at certain points? Chemists called the ‘force’ that caused chemical reactions affinity, but it lacked a clear definition.

During the entire 18th century, the dominate view in regards to heat and light was that put forward by Isaac Newton, called the “Newtonian hypothesis”, which stated that light and heat are forms of matter attracted or repelled by other forms of matter, with forces analogous to gravitation or to chemical affinity.

In the 19th century, the French chemist Marcellin Berthelot and the Danish chemist Julius Thomsen had attempted to quantify affinity using heats of reaction. In 1875, after quantifying the heats of reaction for a large number of compounds, Berthelot proposed the “principle of maximum work” in which all chemical changes occurring without intervention of outside energy tend toward the production of bodies or of a system of bodies which liberate heat.

In addition to this, in 1780 Antoine Lavoisier and Pierre-Simon Laplace laid the foundations of thermochemistry by showing that the heat evolved in a reaction is equal to the heat absorbed in the reverse reaction. They also investigated the specific heat and latent heat of a number of substances, and amounts of heat evolved in combustion. Similarly, in 1840 Swiss chemist Germain Hess formulated the principle that the evolution of heat in a reaction is the same whether the process is accomplished in one-step or in a number of stages. This known as Hess's law. With the advent of the mechanical theory of heat in the early 19th century, Hess’s law came to be viewed as a consequence of the law of conservation of energy.

Based on these and other ideas, Berthelot and Danish chemist Julius Thomsen, as well as others, considered the heat evolved in the formation of a compound as a measure of the affinity, or the work done by the chemical forces. This view, however, was not entirely correct. In 1847, English physicist James Joule showed that raise the temperature of water by turning a paddle wheel in it, thus showing that heat and mechanical work were equivalent or proportion to each other, i.e. approximately, dW α dQ. This was a precursory form of the first law of thermodynamics.

By 1865, the German physicist Rudolf Clausius had showed that this equivalence principle needed amendment. That is, one can use the heat derived from a combustion reaction in a coal furnace to boil water, and use this heat to vaporize steam, and then use the enhanced high pressure energy of the vaporized steam to push a piston. Thus, we might naively reason that one can entirely convert the initial combustion heat of the chemical reaction into the work of pushing the piston. Clausius showed, however, that we need to take into account the work that the molecules of the working body, i.e. the water molecules in the cylinder, do on each other as they pass or transform from one step of or state of the engine cycle to the next, e.g. from (P1,V1) to (P2,V2). Clausius originally called this the “transformation content” of the body, and than later changed the name to entropy. Thus, the heat used to transform the working body of molecule from one state to the next cannot be used to do external work, e.g. to push the piston. Clausius defined this transformation heat as dQ = TdS.

Hence, in 1882, after the introduction of this argument by Clausius, the German scientist Hermann von Helmholtz stated, in opposition to Berthelot and Thomas’ hypothesis that chemical affinity is a measure of the heat of reaction of chemical reaction as based on the principle of maximal work, that affinity is not the heat evolved in the formation of a compound but rather it is the largest quantity of work which can be gained when the reaction is carried out in a reversible manner, e.g. electrical work in a reversible cell. The maximum work is thus regarded as the diminution of the free, or available, energy of the system (Gibbs free energy G at T = constant, P = constant or Helmholtz free energy F at V = constant, P = constant), whilst the heat evolved is usually a measure of the diminution of the total energy of the system (Internal energy). Thus, G or F is the amount of energy “free” for work under the given conditions.

Up until this point, the general view had been such that: “all chemical reactions drive the system to a state of equilibrium in which the affinities of the reactions vanish”. Over the next 60 years, the term affinity came to be replaced with the term free energy. According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Reactions by Gilbert N. Lewis and Merle Randall led to the replacement of the term “affinity” by the term “free energy” in much of the English-speaking world.

I hope this helps? As to a good book, one that I'm reading this week is the 1967 textbook Nonequilibrium Thermodynamics in Biophysics published by Harvard University Press. It’s written by A. Katchalsky (Polymer Chemistry Department, Institute of Science Rehoveth, Israel) and Peter R. Curran (Biophysical Laboratory, Harvard Medical School, Boston Massachusetts). I’m about halfway through the book and it is very juicy. All the derivations are built from the ground up so you don’t miss any key pieces and they are easy to follow. It shows how the Gibbs free energy equation, in an expanded form, can be applied to very exotic situations, such as when the transport of a substance into muscle tissue causes a chemical reaction, which then does the work of stretching or contracting a muscle fiber. Very stimulating book! As to good chemical engineering thermodynamics textbooks, Smith, Van Ness and Abbott’s textbook is good as well as Sandler’s textbook. Adios: --Sadi Carnot 02:10, 30 July 2006 (UTC)


Sadi Carnot, cool, thanks for the explanation and advice :). Rgds: User:Lochnagar (07/30/06)

Should P-V be P-T ?

In the Derivation section,

"Thus, Gibbs energy is most useful for thermochemical processes at constant temperature and pressure: both isothermal and isobaric. Such processes don't move on a P-V diagram; and therefore appear to be thermodynamically static."

if the process is isothermal and isobaric, shouldn't it say, "Such processes don't move on a P-T diagram..."?Brian Wowk 21:32, 3 August 2006 (UTC)

Yes! The Gibbs function is at constant pressure, so specifically includes pV work preformed in changing the volume of a system. Physchim62 (talk) 16:01, 4 August 2006 (UTC)

Upon reflection, I think what the original author meant was that if P and T are fixed, V will also tend to be fixed within a given region of the phase diagram. Thus he described such systems as "thermodynamically static," unless one introduces the chemical potential as an additional state variable. I edited the article to clarify this. Brian Wowk 19:44, 4 August 2006 (UTC)


Please merge Standard Gibbs free energy change of formation here to get rid of a stub which will likely remain undeveloped and which has been tagged for cleanup for over a year, if it's at all possible. Thanks. -THB 02:09, 16 October 2006 (UTC)

Done, thanks: --Sadi Carnot 23:53, 3 November 2006 (UTC)


I fixed the definitions, they were wrong. I kept all the links, I think. PAR 16:41, 20 January 2007 (UTC)

Could you please elaborate on the word "wrong"? Also, what do you think of the use of "main equation" boxes? I saw them on another page somewhere and tried them out here. In your last contrib, the main change you seemed to make was to remove three biological-relevant work terms? I'll add a generic work function, and cleaned your last addition a bit. --Sadi Carnot 10:56, 22 January 2007 (UTC)
Hi Sadi - The definition for a closed system was
That's correct but it kind of begs the question to define G in terms of H since H (which equals U+PV) is just another thermodynamic potential. The internal energy U is the most theoretically fundamental, so I think we should use G=U+PV-TS, showing each conjugate variable (PV and TS). Thats a theoretical viewpoint. I think an experimental chemist will probably want to stress the H. Anyway, using the Euler integration, we can then say G=∑ μi Ni.
The definition for open systems was:
  • The sign on SdT is wrong, it should be negative
  • This is not the equation defining G, it defines an infinitesimal change in G
  • The sign on the sum term involving μ and n is wrong. Also, that term should use N (number of particles) not n (particles per unit volume).
  • The added terms, while correct, should be added on an as-needed basis. The -SdT and VdP terms have wide applicability and must be considered in almost every situation. Other terms may be added for the specific application. To add every conceivable term is impossible, but adding e.g. a term for a contractile fiber makes it sound like this term has a wide range of applicability while it does not.
I think the edits you made since improve things, definitely. For familiarity I wouldn't include the bounding box, I'd aim for something that looks like a journal article, but they don't look bad. PAR 21:17, 23 January 2007 (UTC)
Good eye. I think that when I originally typed that in, I was looking at the expression for dU, and trying to do the rest in my head? We should probably add in, or discuss the use of, the mgh term, to explain how changes in height effect the change in dG. As to the boxes, I’m rather ambivalent…we’ll have to see if anyone else has a comment? Talk later: --Sadi Carnot 01:26, 24 January 2007 (UTC)

I would like to propose a change to the equation "G/N = μ". The equation suppose to be sufficiently accurate only at equilibrium. I propose a comment explaining the distinction between equilibrium and nonequilibrium. The molar Gibbs energy is not the same thing as the chemical potential, especially in non-equilibrium systems. The chemical potential is the partial derivative (the slope) at the selected value, while the molar Gibbs energy is the quotient (secant from origo). ChemGamer (talk) 12:15, 21 July 2008 (UTC)

IUPAC recommendations, consensus, etc.

Related to the discussion on the IUPAC recommendation to use Gibbs energy rather than Gibbs free energy, it should be noted that for the text "Its symbol is ΔGfO", the actual IUPAC recommended notation would be "Its symbol is ΔfGO". This is easy to understand as it then "reads": the change (delta) for formation (f) in Gibbs energy (G) under standard conditions (O). For further details, see p.51&52 of reference 6e. Keeping the apparent consensus in mind, I will not change this now, but should it be decided that IUPAC recommendations are to be followed in the (hopefully near) future, this would have to be corrected as well. Buurma 18:56, 23 January 2007 (UTC)

I understand that it's important to be uniform throughout the world in terms of names and symbols, but this suggestion is an even worse idea than the last one. Hardly anyone uses that notation. Robert Alberty, e.g. in his 2003 Thermodynamics of Biochemical Reactions, uses it, but he is in the minority, this letter after the delta format is probably used in less than 5% of written material. We have to remember that we are writing an encyclopedia not a chemistry journal. Interesting point though. --Sadi Carnot 01:12, 24 January 2007 (UTC)
I'm thinking that this article should get a name change? Principle Chemistry for the Biosciences (Raymond Chang, 2004)is referring to Gibbs free energy as Gibbs energy already. Major textbook for physical chemistry, guys. —The preceding unsigned comment was added by (talk) 02:38, 2 February 2007 (UTC).
See the archive where this point was discussed at some length. Your example is interesting since it was suggested that while all recent straight Physical Chemistry books (i.e. those for chemistry students) used "Gibbs energy", those for the biosciences might not. The problem remains that the term is not only used by chemists, but by engineers and physicists and they still seem to prefer "Gibbs free energy". --Bduke 03:06, 2 February 2007 (UTC)
While there are some situations where Wikipedia should be prescriptive instead of descriptive (for example, insisting that all pictures of experiments display proper safety equipment), nomenclature is not one of them (does Wikipedia use [[β-(benzoylamino)-α-hydroxy-,6,12b-bis-(acetyloxy)-12-(benzoyloxy)-2a,3,4,4a,5,6,9,10,11,12,12a,12b-dodecahydro-4,11-dihydroxy-4a,8,13,13-tetramethyl-5-oxo-7,11-methano-1H-cyclodeca(3,4)benz(1,2-b)oxet-9-ylester,(2aR-(2a-α,4-β,4a-β,6-β,9-α(α-R*,β-S*),11-α,12-α,12a-α,2b-α))-benzenepropanoic acid]] as the primary article name or paclitaxel)? Whether or not textbooks use the word "free" or not, I'd say the majority of actual researchers still use the word "free" in everyday conversations, presentations, etc, so Wikipedia should respect this. Same goes for that delta nonsense.—The preceding unsigned comment was added by (talkcontribs).
I see that I can reply to a few people in one go here.
To Sadi: I obviously checked encyclopaedia and nowhere does it state that an encyclopaedia is based on consensus rather than on definition ;-) I also take slight offence with the sentence "... this suggestion IS an even worse idea than ...". It only IS in your opinion, but your opinion is not necessarily the truth. In my opinion (...) you should have written something along the lines of "I think this is an even worse idea than ...". In any case, going back to the discussion, I just believe that it is important to clearly state on the relevant pages that Gibbs free energy and ΔGfO are the terms/notations that are currently in general use but that it should be noted that these are not the IUPAC recommended terms. By not stating these things clearly, we are actively withholding information from Wikipedia-users which is an activity that I strongly disagree with!
To the previous anonymous poster: I'm taking offence with the notion of "this delta nonsense" and will therefore reply accordingly. Whereas you are probably very proud of your analogy, unfortunately, it's misplaced here. Unless there is an IUPAC recommendation in favour of systematic nomenclature and against trivial names, these cases are simply not comparable. Also, I would like to point out that the full name of paclitaxel is actually given on the page and not withheld from the reader (also see reply to Sadi above).
To Jheald: Agreed - that's what we need to find out (I actually gave finding out a quick try but unsuccessfully so far ...)!
Buurma 19:26, 16 February 2007 (UTC)

Question: did the IUPAC committee ever say why they came to their recommendation? I can't help but feel it seems completely wrong-headed. There are all sorts of different energies out there, but the idea behind the Gibbs energy and the Helmholtz energy is so distinctive, that to me it seems to make enormous sense to identify them together as variants of the same thermodynamic free energy concept.

Rather than just being told "it's the IUPAC recommendation", I'd be more persuadable if somebody could explain to me what the reasoning was that IUPAC put forward.

Otherwise I can't shake a horrible suspicion that IUPAC decided that if there was no way to stop physicists disagreeing with the chemists as to which was the true free energy, to be awarded the prize of the letter F, then IUPAC would take the ball right out of the arena and say that neither concept was to be called a free energy, so neither should get the letter.

And two fingers to the value lost by losing the word "free".

No doubt that isn't what happened at all, but can anyone point to any good reasons given by IUPAC for their recommendation ? Jheald 14:25, 2 February 2007 (UTC)

I don't know of any "official" explanation. My speculation is that it is due to an ambiguity in the French translation (IUPAC nomenclature has to be easily translated). Energie libre can only refer to the Helmholz variety, while the Gibbs free energy is referred to as enthalpie libre ("free enthalpy"). Physchim62 (talk) 10:36, 8 February 2007 (UTC)
  • Comment: I'm responding to the RFC request. I am much more familiar with the term "Gibbs Free Energy" than "Gibbs Energy". However, my guess is that the IUPAC recommendation is likely to be based on not getting confused with Helmholzt Free Energy. To be honest, I think we should stick with the more common Gibbs Free Energy (unless evidence is shown that it's not more common in which case Gibbs energy would be fine). In general though, it's not that important... -SocratesJedi | Talk 22:16, 2 February 2007 (UTC)
Agreed. Thanks for commenting. We reached the same consensus in the last archive. --Sadi Carnot 17:16, 3 February 2007 (UTC)
The legacy term "Gibbs free energy" is still widely used in chemical thermodynamics, but people in my field are turning toward omitting the "free". The reason is the problem of specifying what portion of the Gibbs energy is actually free for conversion to other energy forms. The fraction varies depending on (at least) the source material, the type of transformation, and the amount of energy transferred. The problem increases as more constraints are added to the necessary material balance. We also use the index of the delta for describing which type of transformation the quantity refers to. The index of the letter for the fundamental energy (G for Gibbs energy) is reserved for "m" meaning molar, or a formula for the species, reaction or component in question. The energy change for a transition between octanol and water use both the upper and lower indices of the delta. In electrochemistry, one sometimes needs a place for reporting the electrode. On another matter, although it should not need to be pointed out. The Helmholz free energy is not the same as the Gibbs free energy, but they are currently mixed in the spurious term "Free energy" used by an alarmingly large number of biochemists. ChemGamer (talk) 12:03, 21 July 2008 (UTC)


You can't have it both ways. Either the chemical potential has units of joules/particle and N has units of particle, or the chemical potential has units of joules and N is dimensionless. I am very much in favor of the first option, so I have changed it accordingly. If there is disagreement, we should at least agree that the product μN should have units of joules. PAR 22:03, 2 February 2007 (UTC)

What do the standard bodies say? What you are "very much in favor of" is not a reason. A chemist would say that the Gibbs Energy for an arbitary amount of material has units of Joule (extensive), but results would be published as the intensive unit, Joule/mole. --Bduke 22:32, 2 February 2007 (UTC)
Yes, right. If you have the chemical potential in joules/mole, then you multiply by N in moles to get the energy in joules. In exactly the same way, if you have the chemical potential in joules/particle, then you multiply by the number of particles to get the energy in joules. Chemists like the first way, physicists the second. (The molar Gibbs free energy is just a different name for the chemical potential in joules/mole)
When I said I preferred μ in joules/particle and N in particles, I meant that I preferred it over μ in joules and N dimensionless. When it comes to μ in joules/particle or joules/mole, I have no formal objection to either, although being a physicist, I am more comfortable with particles than moles.
My point was that the μ, N, and their product must be dimensionally consistent. You can't have μ in joules/particle, N dimensionless, and μN in joules. PAR 00:09, 3 February 2007 (UTC)
Short on time, but off the top of my head, according to Gibbs (from memory), N is particle number (crossing the system boundary), μ is the differential change in the internal energy U of the system when one particle crosses the boundary. --Sadi Carnot 17:15, 3 February 2007 (UTC)
Right, but to be maniacally rigorous, the chemical potential is the (partial) derivative of internal energy with respect to particle number, which is slightly different. The slight difference is unimportant for everyday size objects since a single particle is such a small fraction of the whole, but for a smaller number of particles, it may be significant. PAR 17:53, 3 February 2007 (UTC)

I think essentially that the definition is “energy change per amount of substance”; however, “amount” can be defined as mass, moles, particles, etc.; moreover, the “energy” can change per application as well, such as chemical potential defined in terms of U, H, F, or G. Per “amount”, however, I checked a few sources and it’s usually either per unit “particle” or per unit “mols”. I added two sources to clarify this. --Sadi Carnot 02:00, 10 February 2007 (UTC)

The SI unit of "amount" is the mole. Amount and mass are not the same. You can talk about the energy change per kilogram, but it is not “energy change per amount of substance”. --Bduke 02:31, 10 February 2007 (UTC)
The chemical potential is defined as the partial derivative of the internal energy but it is equal to the partial derivatives of the other fundamental energies as well. The unit is joules per mole or joules per particle. The former is used in chemical thermodynamics while the latter is used in statistical thermodynamics. The extensive variable (particle count) is never dimensionless, it has either a unit of moles or the unit "particles". ChemGamer (talk) 12:02, 21 July 2008 (UTC)


The data is currently given in terms of (some indeterminate) "cal" — see calorie. Should be SI.
—DIV ( (talk) 04:34, 1 April 2008 (UTC))


I know this may not be the correct place but I need some help with calculating the Enthalpy (ΔH) of a reaction given the following data:

  • Mass of salt that dissolved in 5ml water
  • Temperature at which it completely dissolves
  • Mass of Salt in solution of water
  • Mole of Salt in 100 g solution water
  • Density of solution at 20 Degrees celcius
  • Density of solution at Temperature in which it dissolves
  • Volume of 100g of solution
  • Molarity of salt
  • Equilibrium constant

Tourskin 19:51, 23 March 2007 (UTC)