Talk:Gibbs free energy

message: i think that gibbs free energy just means that if the internal energy of the sysyem is greater than the energy needed to preform the reaction, it will be spontaeous.  —Preceding unsigned comment added by 75.28.97.33 (talk) 11:10, 1 February 2008 (UTC)
thread_title:  Good Article 

message: '''
I hope I don't come off as unappreciative of all the time you guys are putting into these pages but...
Is it just me or is the below, which is in bold, completely incomprehensible?
Gibbs defined what he called the “available energy” of a body as such:
The greatest amount of mechanical work which can be obtained from a given quantity of a certain substance in a given initial state, without increasing its total volume or allowing heat to pass to or from external bodies, except such as at the close of the processes are left in their initial condition.
::::::For what it is worth Microsoft Word's grammar check didn't flag it
I appreciate that you can't be holding the hand of a beginner like me but Wikipedia should be a place for a guy like me to go to when he wants to understand something like Gibbs Free Energy. My inability to understand the way that they spoke in 1873 should not be what holds me back.
:The year 1873 is Gibbs. No one, I believe, can read all of Gibb's reasoning. It's not the language. Try Pierre Duhem's 'Thermodynamics and Chemistry' on Google Books. The sections on equlibrium and stability are the clearest I've read. Geologist (talk) 01:22, 10 December 2010 (UTC)
thread_title:  Feedback 

message: What do your extensive properties have to do with the integration-ability of the equation in the "derivation"? Do you mean to say "since these variables are usually constants?" Are you guys trying to use as few words as possible? Would it be too much trouble to elaborate on these steps? kthxBye.  — Preceding unsigned comment added by 174.26.57.26 (talk) 20:47, 4 October 2013 (UTC)
thread_title: Moar Feedbacks

message: This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:52, 10 November 2007 (UTC)
thread_title:  WikiProject class rating

message: So, I removed this section relating entropy and life. It doesn't seem to fit in with the rest of the article. --HappyCamper (talk) 20:11, 22 December 2007 (UTC)
thread_title:  Removed section 

message: The second sentence of this article does not make sense:
Technically, the Gibbs free energy is the maximum amount of non-expansion work which can be extracted from a closed system or this maximum can be attained only in a completely reversible process.
I'm not sure what the writer is trying to say.  —Preceding unsigned comment added by 78.149.104.116 (talk) 23:23, 8 February 2008 (UTC)
replies: text: Doesn't the reference to 'non-expansive work' refer to a different characteristic function, such as Helmholtz's? A system rolls along the Gibbs function's minimum as the system travels along an equilibrium path slow enough to keep the system uniform in temperature, pressure, and escaping tendencies of chemical substances. The Gibbs-Duhem equation and Duhem's Theorem allow one to calculate the thermodynamic properties of each substance in this open system. I never use the concept of 'free', but perhaps it fits in here. Geologist (talk) 01:22, 10 December 2010 (UTC)
thread_title: Second Sentence

message: I think it would be useful to put in the article dGo' (supposed to be a delta symbol, the letter G, a degrees sign, and an apostrophe), the definition of working in a biological system. I don't know how to format the text or where to insert it at. An example of such notation is found here http://www.sci.sdsu.edu/class/bio202/TFrey/ThermoEnzymes.html (section VIII, portion C, entry 7). AStudent (talk) 08:57, 28 May 2009 (UTC)
thread_title:  STP delta G prime 

message: The statement
'The equation can also be seen from the perspective of both the system and its surroundings (the universe).'
is confusing, since it implies at first reading that the surroundings are the universe.
:They should be the same. Being a geologist, I prefer 'system' and 'environment'. Heat and work shuffle back and forth. Geologist (talk) 01:22, 10 December 2010 (UTC)
thread_title:  Overview 

message: My knowledge of thermodynamics is very limited so my questions refer only to the mathematics of the derivation.
In the section Derivation:
1. I don't see why it is necessary to integrate dG to obtain equation (8) for G. Simply comparing equations (2) and (3) leads to the same result.
:The above point is well taken. The derivation is foreign to me, and switches between functions of state and their total derivatives, not partial (which should be there if something is held constant). Internal energy (which I avoid for methodological reasons) is converted into Gibbs Energy. These are just characteristic functions, functions whose extreme point is at equilibrium at constant V, S, and N(i) and that at a chemist's lab conditions: constant p, T, and mu(i). The Gibbs function (a characteristic function) varies with pressure and temperature, and this is not indicated by the final equation. Geologist (talk) 01:22, 10 December 2010 (UTC)
replies: text: Equation 6 is, I believe, wrong. It should read, I believe, dG = total derivative of -pV, TS, sum M(i) d(mu(i)) (Gibbs, eq 88). Each term has two differentials. From this, one step will subtract half and derive the Gibbs-Duhem equation, an identity which is very similar to your correctly derived identity. The latter has vast applications, and is valid for equilibrium, open systems. Geologist (talk) 01:22, 10 December 2010 (UTC)
thread_title:  A possibly stupid question 

message: Please don't ignore DanielGenin's query, which draws attention (I believe) to a very serious typo. The section 'Definitions' also needs two typos fixed. One substitutes a(i) for mu(i) and the other has some confusion with N(i).
Could someone please change Gibbs's description as an 'American Engineer' to American Scientist?  We think of Joseph Conrad as a writer, not a custom's agent; and Charles Pierce as a philosopher, not Coast Guard employee (though he was a scientist there).
(It may be hard to believe, but in the 19th Century faculty in different Departments actually spoke. Even geologists lunched with physicists: the discovery of eutectics was used immediately by Teall to explain the textures of some granites.) Gibbs was one of the greatest scientists of the 19th Century. You probably know him for his correct invention and extensive development theorems in chemical thermodynamics and for the notation you learned in advanced calculus. Few remember him for his dissertation on gears:-) Thanks!) Geologist (talk) 01:22, 10 December 2010 (UTC)
thread_title: =

message: There is an image at Wikimedia Commons if it's useful, not my area.ref1--Billymac00 (talk) 06:12, 26 December 2010 (UTC)
thread_title:  Image  

message: This has been said by so many people for such a long time, perhaps starting with Hamilton but probably even before him, that I believe asking for a citation there is unnecessary. What are your thoughts about this? Moreover, I don't see why there would be any need for the system to be in STP in order for this general rule of thumb to be true... 201.137.10.188 (talk) 06:21, 5 January 2012 (UTC)
replies: text: This is completely wrong. Changes can only occur when they result in the increase of universal entropy. (Ref: Peter Atkins' Physical Chemistry). A transfer of heat from a hot body to a cold body will always result in an increase in total entropy. Entropy can always be created by turning energy into heat. Since energy can neither be created nor destroyed a decrease of total energy (including work or heat) in one part of the universe will necessitate the increase in total energy in another part of the universe. Therefore if the argument that "Every system seeks to achieve a minimum free energy" is true, why then should this other part of the universe accept an energy transfer into it? The numerical value of a Gibbs function is such that if its value is positive, then the changes as written will give rise to a decrease in entropy, and therefore cannot happen. If the value is negative, then there is an overall increase in entropy and is therefore allowed. If the value is zero, then the process is in equilibrium. It also turns out from the mathematics that at a constant pressure, the numerical value of the Gibbs function is the maximum amount of non-expansion (including contraction) work (such as electrical work) that the system of changes can do. 81.129.179.74 (talk) 12:56, 5 February 2013 (UTC)
thread_title:  There is no need to cite the quote of "Every system seeks to achieve a minimum free energy" 

message: The two-dimensional graph from Gibbs's 1873 paper carries a caption that says that the length AB is the Gibbs free energy.  I don't think this can be right, since the graph is labelled as being a slice through constant volume (I also checked the original source). That must mean that AB is what modernly is called the Helmholtz free energy.  I corrected this in the caption on the wikibio of Gibbs, which I've been editing extensively.  I think someone should look after the other uses of that image in Wikipedia.  - Eb.hoop (talk) 19:33, 25 February 2012 (UTC)
thread_title:  Graphs from Gibbs's paper 

message: The Gibbs free energy is in general
:G = U - TS + PV
The article seamlessly jumps into a special case of a homogeneous liquid or gas, giving
:G = \sum_i \mu_i N_i  
but not all systems are homogeneous. For a physics example, consider an electron system with electron-electron interactions [].
In chemistry, inhomogeneity can come when you start to consider adhesion of chemicals to the walls of the beaker, walls whose surface area does not grow proportional to volume. --Nanite (talk) 13:12, 26 May 2013 (UTC)
thread_title:  Be careful, not all systems are homogeneous 

message: let me know if it's unnecessary or could use improvements.  — Preceding unsigned comment added by 71.57.71.55 (talk) 07:00, 24 December 2013 (UTC)
thread_title:  added section on coupling reactions in biological systems 

message: In the current article, it said (before my edit) that the Helmholtz free energy is for systems at constant volume and temperature.
In the article on Helmholtz free energy, it says the Helmholtz free energy is for systems at constant temperature.
So I changed the current article to agree with the Helmholtz article.
But is this correct? And why or why not?
178.38.83.46 (talk) 07:49, 9 March 2015 (UTC)
thread_title:  Removed the term "constant volume" for Helmholtz free energy 

message: 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 T = constant, V = constant), whilst the heat given out is usually a measure of the diminution of the total energy of the system (internal energy).
This can't be right. By conservation of energy, the change in the internal energy U must equal the amount of energy that leaves the system, which is heat plus work. 
Why does the article say that the heat given out is "usually" a "measure" of the diminution of the internal energy? The only thing that prevents this from being outright wrong is the use of vague language. In any case, it clouds the issue.
178.38.83.46 (talk) 10:33, 9 March 2015 (UTC)
thread_title:  Heat equals change in U? I doubt it 

message: Why does the intro show Gibbs represented by delta P when the rest of the article uses delta G, which seems widely used elsewhere? Gwideman (talk) 02:52, 16 July 2015 (UTC)
thread_title:  Gibbs represented by P or G? 

message: The statement "Gibbs free energy is a thermodynamic potential that measures the maximum or reversible work that may be performed by a thermodynamic system at a constant temperature and pressure" is not correct!  It is the negative of the change in Gibbs free energy that measures the reversible work.  If there's not objection, I would make the necessary correction.--LaoChen (talk)06:41, 18 May 2016 (UTC)
thread_title:  lead section 

message: Please avoid using ‘Spanish masculine ordinal indicator’ in equations like ΔGº = ΔHº-TΔSº.  I was completely confused what the hell it the underscored o is doing there.  Not sure what actual mathematical symbol is supposed to be there, so cannot fix it.  — Preceding unsigned comment added by 147.229.99.101 (talk) 11:09, 10 April 2018 (UTC)
thread_title:  Confusing notation 

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thread_title:  External links modified 

message: There is currently a tag at the top of this article that says it may be too technical. The tag is dated April 2018. As I look through the comments, the only ones that complain about it being too complicated are much, much older than that. This is a complex subject. I have had a year of college physics and that was forever ago. I came to this article because this topic came up recently in a discussion on information and I wanted to get the basic idea. The article seems clear and well written to me. Does anyone have any specifics as to why the article is too technical? If not then I’m going to remove the tag --MadScientistX11 (talk) 02:33, 7 July 2020 (UTC)
replies: text: I agree that the tag should be removed. This article is written quite clearly for anyone who has had a course in calculus. The only section that seems too technical is the one on Graphical interpretation, which could be moved further down as it is not really necessary to understand the rest of the article. Dirac66 (talk) 11:22, 7 July 2020 (UTC)
replies: text: Sounds good. Since no one has objected I'll take this as a consensus and am removing the tag. --MadScientistX11 (talk) 15:47, 8 July 2020 (UTC)
replies: text: OK. And I have now moved the Graphical interpretation section to the end of the article, since this is the only section which really does seem too technical. And not in any textbook which I have read. Dirac66 (talk) 20:06, 8 July 2020 (UTC)
thread_title:  Technical Tag Justification? 

message: Assuming the superscripts in   p^\circ, V^\circ or  T^\circ  indicate the standard states (1atm, 298K)
Given that
:p V = R T   
and  
:p^\circ V^\circ = R T^\circ 
These two statements 1 and 2 below seem contradictory.  
Is the {G^\circ} in Statement 1 the same as the {G^\circ} in the Statement 2 ? 
This needs an explanation.   
The sentence "If the volume is known rather than pressure" is not precise enough.   
Statement 1   
The temperature dependence of the Gibbs energy for an ideal gas is given by the Gibbs–Helmholtz equation, and its pressure dependence is given by
:\frac{G}{N} = \frac{G^\circ}{N} + kT\ln \frac{p}{p^\circ}.
Statement 2   
If the volume is known rather than pressure, then it becomes
:\frac{G}{N} = \frac{G^\circ}{N} + kT\ln \frac{V^\circ}{V},
Above comment by editor Maajdi on 7 March 2021.
:Statement 1 is the usual textbook version. I will add Atkins and de Paula as a source.
:Statement 2 is derived from statement 1 using :p^\circ V^\circ = p V  for an ideal gas at constant temperature (Boyle's law). However statement 2 is not found in textbooks that I know of, so for Wikipedia it counts as unsourced and even original research. And as you say its meaning is not precise enough because it is not too clear exactly which volumes we are talking about. I will remove statement 2, which was added by a numbered editor in 2007 with no further comment. Dirac66 (talk) 21:01, 26 March 2021 (UTC)
thread_title:  Clarify: pressure dependence  versus  volume dependence