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Interestingly, the definitions in the German and English articles describe a different quantity. As I know it, activity is unitless, but defined against an arbitrary standard 1 mol dm-3. Therefore, a concentration of 1.0 mol dm-3 and a coefficient of 0.9 gives an activity of 0.9. --
Vuo21:35, 19 September 2006 (UTC)reply
Thanks! Do you have any examples that involve specific solutions that might be well-known?
"unitless, but defined against an arbitrary standard", at least to me, appears to make no sense whatsoever. A concentration of 1 mol/l and a coefficient of .9 should surely give an activity of .9?
not really suggesting doing anything, yet, but in the interest of the sanity of any high school students who might not be allowed the same sloppiness with units in their science classes, I'd like to see sloppy use of units clearly marked on WP, I guess ...
The activity in Chemistry is one of the few units which doesn't have a unit. So this is completely normal(It's because when you divide mol.L-1 with mol.L-1 the result has no unit).
Usable definition, exact as it was defined
Original Lewis' definition is:
so ratio of fugacities. DEfinition is valid for SOLIDS, LIQUIDES and GASES (not only for gases)!!
You can choose denominator (reference fugacity) arbitrarily !!
(only the usage is 101325 as perfect gas for gasses, and fugacity of pure component for solids)
Obviously the french and german articals cannot be merged without translation. If users who speak french or german or preferrably both could judge which is best it could be requested that that article be translated and merged with the english article.
Vuo Has already suggested that the French article has a lot of good content what are others peoples views and it could then be requested for translation from whichever comes out on top. --
Ksbrown21:03, 22 September 2006 (UTC)reply
The french article was merged with the english article and no original information from the english article was lost. The translation was done by
SamiKaero. -
Ksbrown17:04, 24 October 2006 (UTC)reply
Thanks for this proposal. I was unaware of the existence of
Activity coefficient when I re-vamped this article. Obviously that article is more comprehensive. What, if anything, do you think should be kept from this one?
Perhaps both articles are needed because it it a vast area. My understanding was that the article on activity coefficient will focus on how to practically calculate the activity coefficients in the specific cases, and not dwell on what activity is. This is similar to the situation in articles "equilibrium"-"equilibrium constant", "heat transfer"-"heat transfer coefficient", and numerous others. Just my C$0.02.
Stan J. Klimas (
talk)
14:40, 16 February 2008 (UTC)reply
P*solvent and Ksolute
Hi. Would it be possible for somebody to write explicitly what P*solvent and Ksolute in section
"definition" are? Thanks!
If the chemical potential of pure liquid is denoted , then the chemical potential of in an ideal solution is
I guess, that depends on T and p as well: .
Whereas here at
Activity (chemistry) one finds
In
ideal mixtures we can write the dependency of the
chemical potential of a species i on the composition (written as mole fraction x of i) as:
and µi0 is the value of µi under standard conditions.
This means, that is only function of the temperature and not the pressure, since the pressure is to be taken at . But then where has the pressure dependence of in this second formula disappeared?
--szaboka
87.184.93.231 (
talk)
17:16, 27 November 2008 (UTC)reply
Gas constant
I suspect that in the page the gas constant R is erroneously used instead of the Boltzmann constant kB, but I may be wrong, as it depends on the units of measure. Can someone comment?
E prova sta beta (
talk)
13:23, 16 September 2009 (UTC)reply
The values R and kB are the same, just multiplied by
avagadro's number. R and kB are both the same constant, but the units can be chosen arbitrarily, provided that they can be converted back to either j/(mol.K) or j/(at.K). Engineers and chemists tend to prefer R, and physicists tend to prefer kb. See
Boltzmann_constantUser A1 (
talk)
02:19, 17 September 2009 (UTC)reply
How do people feel about reconfiguring some of the notation used in the article. The amount fraction (or mole fraction), which is denoted as "x", appears quite often due to its connection with activity. However, it is important to note that when a solution is in equilibrium with its vapor, the mole fractions of each component are not the same in the solution and gas phases. Would people be opposed to using the notation "y" for the gas-phase mole fraction and "x" for solution-phase mole fraction? This is a fairly common "modern" notation that many texts have adopted.
Sirsparksalot (
talk)
16:16, 8 December 2012 (UTC)reply
If we include a mention of solution-vapour equilibrium, then I agree that we need two symbols for the two values of mole fraction, as in the
Raoult's law article (where I see that 3 weeks ago you defined the symbols for the equation with yi and xi and also explained why the equation is useful - thank you). However at the moment such equilibria don't seem to be in the article, so what notation now in the article would you reconfigure?
Dirac66 (
talk)
19:42, 8 December 2012 (UTC)reply
My main reasoning for such a change was due to the fact that activities are discussed in context of both gases and solutions and that the solution sections don't explicitly state that xi is the mole fraction in the solution. Since most solutions of practical interest are made with volatile components, they will be in some sort of equilibrium with the vapor. In fact, isn't this how most solution activities are determined, by making use of this equilibrium to equate the chemical potentials of the the gas and solution? I have had several conversations with people who get confused when discussing Raoult's law because they want to use xi (which is typically used to represent the solution mole fraction) to determine the partial pressure in the gas phase using Dalton's law (which also uses xi when discussed on its own). (I should admit that I was one of these people myself when first learning about Raoult's law. :) ) I have found it convenient to adopt the yi/xi notation that several texts use to avoid the confusion. In any case, it is only a minor edit, but wanted to run it by people before investing time and effort on something that people may not like. PS - Thanks for fixing my typo, don't know how I missed that.
Sirsparksalot (
talk)
00:13, 9 December 2012 (UTC)reply
OK, I understand the reason, but I am still trying to understand exactly where you want to make the changes. I think the best way (and perhaps the way you mean) would be to systematically use yi for all mention of gas-phase mole fractions. Note that the
Dalton's law article now does use yi, and the
mole fraction article mentions (last sentence of intro) that the IUPAC Gold Book recommends y for gas mixtures.
So what to change? The subsection Standard states#Gases has 3 x's which can all be changed to y. And the subsections Definition#Activity coefficient and Standard states#Mixtures in general have some x's which can refer to either gas or solution, so we need to point out that they are x in solution but y in gas. But probably not every time x is used, as it would become repetitious.
Dirac66 (
talk)
03:08, 9 December 2012 (UTC)reply
Yes, that is essentially what I meant, to replace all gas-phase mole fractions with yi. Although, now that you mention it, it is more difficult than I had initially thought due to the "mixtures in general" parts of the article. I'll see what I can put together then maybe put up a test version to see what other people think about the changes before I commit to anything.
Sirsparksalot (
talk)
19:55, 10 December 2012 (UTC)reply
I don't understand why this redirected to the disambiguation page. I've fixed it and tried to write a bit of an article from other sources on the net, but I'm only here because I was looking for information, and I'm not an expert on the topic. Please, chemists, help me!!!
I was commenting on the article Carbonic Acid and attempted to link to this article and was not able to.
I tried both the following (ignore the "." I use as separator): [.[Thermodynamic activity].] and [.[Thermodynamic_activity].]
Also, the disambiguation page on Activity doesn't have this article, rather the Activity (Chemical) link redirects to here. Could someone who knows what they're doing fix this? Thanks.
173.189.72.93 (
talk)
23:23, 18 November 2014 (UTC)reply
Chemical Potential or Molar Chemical Potential?
Currently, this page defines relative thermodynamic activity as
"where μi is the
chemical potential of the species i under the conditions of interest, μo i is the chemical potential of that species under some defined set of standard conditions."
Given that the universal gas constant R is used, and not Boltzmann's constant k, shouldn't μi be the molar chemical potential and not the chemical potential?
--
Physicsman19 (
talk)
17:08, 22 October 2018 (UTC)!reply
It is true that molar chemical potential would be more logical, but tradition is just to say chemical potential, as in the IUPAC source and in textbooks. I will add the word (molar) in parentheses, to show that it really is a molar quantity even though the word molar is not usually specified.
Dirac66 (
talk)
15:09, 24 October 2018 (UTC)reply