Talk:Henry's law

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Help with this template Comments: edit – history – watch – refresh I have rated this article as Class=A and Importance=High. I would first like to say that this article is most important to Engineers and Chemists. I would not have categorized it as a Physics article. It is of very high importance to chemists and engineers (particlurly chemical engineers) working in a great many industries . I have classified it as Class A because it has been well-written, extremely well referenced, and organized well as per Wikipedia practice. It serves a highly useful function by documenting the fact that there two commonly used expressions for the Henry Law (each the invert of the other) and they are often confused one for the other. It also serves a useful function in exemplifying how to convert from one set of units to another since there are many sets of units in use.- mbeychok 02:19, 4 December 2006 (UTC)

Contents 1 Reason for moving some of the article 2 Is Like-A-Fish really relevant to this article? 3 Reason for modifying the table 4 Reason for deleting most of Sept. 17, 2006 edit by 66.27.139.36 5 Reason for reverting changes by 129.2.198.192 6 Reason for reverting changes by 69.200.224.11 7 Interpretation of Henry's Law 8 Reason for reverting change of equation by 155.198.109.41 9 Converting between the constants units

[edit] Reason for moving some of the article

I have moved the text below from the article to here, because it's not very encyclopaedic, and I'm sure a less-than-cursory search of the literature would shed some light on it. I don't know enough to say what of this is accurate and what's not - hope someone else might. Worldtraveller 22:43, 26 Mar 2005 (UTC)

Addendum 2005

A cursory search of the literature has not revealed what effect a temperature difference between gas and liquid would have. It is hereby maintained that increasing the temperature of either medium has the effect of increasing the partial pressure or concentration of that medium.

When a temperature difference is introduced the effect of this addendum is to cause thermal diffusion with flow of solute molecules from warm to cool in the liquid solvent and across the gas/liquid interface as required to achieve a new balance.

This mechanism can be demonstrated by filling a glass with freshly opened soda water from the refrigerator and putting a fresh ice cube from the freezer in the liquid. It will be observed that gas bubbles do not precipitate on the glass as one might expect, because of reduced solubility, but rather on the ice. This demonstrates that carbon dioxide molecules flow down the temperature gradient in the liquid and across the liquid surface from a relatively dilute solution into 100% carbon dioxide. This is a very potent thermal diffusion effect considering that temperature differences are very small.

Further note 2006

Henry's Law can be used to prove that interface diffusion does occur. Should the solute concentration in either medium be changed the concentration in the other has to change to produce a new balance. For this to happen there must be diffusion across the interface, something that is not accepted by mainstream climatology.

If interface diffusion is not accepted then of course a thermal diffusion effect cannot be accepted.

It could be argued that the carbon dioxide example chosen does not obey Henry's law because it reacts with water to form a carbonate. In addition there is, as far as I know, no listing for thermal diffusion for the transport of matter in Wikipedia, only for heat dispersion. Thermal diffusion of matter is well known to happen. Hydrogen,for example, migrates down the temperature gradient in zirconium alloy pressure tubes. It seems however, to have been missed and since it was, and since CO2 is not ideal, it was assumed that there would be sufficient grist for a challenge.

== The values for oxygen, carbon dioxide and hydrogen have the wrong units ==

The following values of the Henry's Law constants are those given in the current article:

*O₂ : 4.34×10⁴ L·atm/mol>/s>

*CO₂ : 1.64×10³ L·atm/mol

*H₂ : 7.04×10⁴ L·atm/mol

The units above are incorrect are incorrect. The correct units are:

*O₂ : 4.34×10⁴ atm/(mol fraction)

*CO₂ : 1.64×10³ atm/(mol fraction)

*H₂ : 7.04×10⁴ atm/(mol fraction)

See [1] which gives almost exactly the same numerical values as given in the current article but also has the correct units:

*O₂ : 4.32×10⁴ atm/(mol fraction)

*CO₂ : 1.64×10³ atm/(mol fraction)

*H₂ : 7.06×10⁴ atm/(mol fraction)

Also see [2] and download the .pdf file listing a great many Henry's Law constants. This source defines k = C/P which is the inverse of the k=P/C used in this Wikipedia article. Therefore, the values from the downloaded .pdf file were inverted to obtain:

*O₂ : 769.2 L·atm/mol     which converts to 4.27×10⁴ atm/(mol fraction)

*CO₂ : 29.4 L·atm/mol     which converts to 1.63×10⁴ atm/(mol fraction)

*H₂ : 1282.1 L·atm/mol     which converts to 7.12×10⁴ atm/(mol fraction)

Also note that the downloaded .pdf file uses the solution molarity, M = (mols of gas)/(liter of solution) to express the concentration C of the solution ... which is the same as using mol/L.

As can be seen, both of the sources I have referenced above are in very close agreement with each other. I am accordingly revising the values in this Wikipedia article to show the correct units.

I must say that I am dismayed that the incorrect units were not noticed much earlier. - mbeychok 05:46, 14 June 2006 (UTC)

[edit] Is Like-A-Fish really relevant to this article?

I don't want to be a spoil sport but are Like-A-Fish in the "See also" section and New 'no air tanks' diving system, based on Henry's law in the "External links" section really relevant to this article? To me, they seem to be advertising for the same company. I really see no connection between that diving air invention and Henry's Law. Am I being too harsh? - mbeychok 06:27, 14 June 2006 (UTC)

[edit] Reason for modifying the table

The table which user:NickFr added to this article is very helpful and enhances the article. I modified it somewhat to make the definitions of the parameters more explanatory or precise. I also modified the sections above the table so that they were consistent with the table. - mbeychok 19:59, 30 August 2006 (UTC)

[edit] Reason for deleting most of Sept. 17, 2006 edit by 66.27.139.36

The edit by 66.27.139.36 had some interesting material about carbonic acid but most of it had absolutely nothing to do with Henry's Law. It really belongs in a more appropriate article or in an article of its own. I left in the one sentence "A common example of a gas that reacts with the solvent is carbon dioxide, which reacts rapidly with water to form hydrated carbon dioxide and then forms carbonic acid (H₂CO₃)." because that sentence is appropriate here ... but all the rest of the edit was deleted. - mbeychok 21:14, 17 September 2006 (UTC)

[edit] Reason for reverting changes by 129.2.198.192

129.2.198.192:

If you will read the entire article, especially the section on Other Forms of Henry's Law, it discusses the fact that the equation you used is simply the invert of the original equation. The examples given in units of L•atm/mol are correct for the original equation and incorrect for your inverted version. See the table in the section on "Other Forms of Henry's Law".

Please do not change the equation again. Regards, - mbeychok 19:03, 6 December 2006 (UTC)

[edit] Reason for reverting changes by 69.200.224.11

69.200.224.11:

This has come up before ... see the comment just above. It applies to your changes as well. Read the entire article and read it thoroughly. Please do not change the equation again. Regards, - mbeychok 00:08, 21 January 2007 (UTC)

I see that you have changed it back, so please disregard my above remark. But please be careful when experimenting like that. - mbeychok 00:33, 21 January 2007 (UTC)

[edit] Interpretation of Henry's Law

This article does a good job of describing Henry's law, but fails to give an explanation of why it is true. I found a reference page[3] that discusses the matter, but in an unscientific manner. I believe that a section similar to the following should be added to the article.

Henry's law can be explained by the fact that there is a fixed probability that a gas molecule will encounter the surface of a liquid. Similarly, there is an equal probability that a gas molecule dissolved in the liquid will escape the surface of the liquid and return to the gas. Since these two quantities are equal, the rate of dissolving and undissolving of a type of gas are equal. Thus, there is a constant but equal exchange of any one type of gas molecule between the liquid and the gas mixture that is determined only by the concentration of that type of gas.[4]

Ok, that's a start, but it's a bit wordy. Please recommend any changes that need to be made to improve it.

Is there another term for undissolve?

Is the reference I provided good enough for encyclopedia use?

Doctorrockandroll 02:19, 3 February 2007 (UTC)doctorrockandroll

To answer your final question quite candidly, my opinion is that it is not good enough for use here. To me, it is written down at about the level of a 10-12 year old pre-teenager.

Also, when you start using words like "molecule", "probability", and "concentration of gas" you defeat your own purpose of trying to write down to the level of pre-teenagers because they won't know what those terms mean. They may think they do, but they won't really understand them. As for "gases undissolving", one could use "gases escaping from the liquid solution".

In general, I oppose writing down or speaking down to readers to the point where the technical integrity of the article is no longer maintained. I don't think you would find the sort of explanation (as you propose) in the Encyclopedia Britannica and I see no reason why a technical article in Wikipedia should be written for pre-teenagers. For example, I see where you did some minor editing of the Intermediate frequency article's mention of "superheterdyne receivers". I haven't the faintest notion of what is meant by "intermediate frequency" or "superheterodyne receivers" ... but I don't expect that article to dumb itself down to where I understood it. If I were interested in radios and wanted to understand that article, I would buckle down and do some studying and reading until I did have enough knowledge to understand it. - mbeychok 06:01, 3 February 2007 (UTC)

[edit] Reason for reverting change of equation by 155.198.109.41

55.198.109.41:

If you will read the entire article, especially the section on Other Forms of Henry's Law, it discusses the fact that the equation you used is simply the invert of the original equation. The examples given in units of L•atm/mol are correct for the original equation and incorrect for your inverted version. See the table in the section on "Other Forms of Henry's Law".

This has happened a number of times before because people do not read the entire article thoroughly before making a change. Please do not change the equation again. Regards, - mbeychok 17:42, 6 March 2007 (UTC)

[edit] Converting between the constants units

How does one convert between a K with the unit Atm/(mole fraction) and L*Atm/mol ? Thanks 67.79.200.162 22:14, 28 March 2007 (UTC)confused person

I assume that you meant to ask about the Henry's law k (rather than K). The easiest way to convert between the two units you asked about is to use the values in Table 1 of the article to find that:

L*atm/mol = [atm/(mol fraction)] ÷ 55.4

If you want the actual dimensional conversion, send me your email address and I will send it to you as a Microsoft Word document. To email me, go to my user page, scroll down the left hand frame and click on "Email this user". - mbeychok 22:56, 28 March 2007 (UTC)

Thank you for your help. They differ by a factor of approximately 55.4 up or down a little depending on the gas. This weekend I will figure out the conversion when I don't have to spend most my time working. Anyways, over at <a href="http://webbook.nist.gov/cgi/cbook.cgi?ID=C64175&Units=SI&Mask=10#Solubility">NIST</a> here are henry's constants and they use mole/kg*bar. The reason this all sparked my interest started on <a href="http://forums.austin.craigslist.org/?ID=60666084"> craiglist forum.</a> The best way to look at situation is see slope of rault's law and henry's law I thought but I got hung up on units. 67.79.200.162 16:19, 30 March 2007 (UTC)confused person

My offer to email you the conversion is still open. The reason the conversion factors you found in Table 1 vary slightly from 55.4 is not because the gases are different ... they differ slightly because of rounding off of the various k values.

I am not surprised that NIST used other dimensional units. I have seen, quite literally, a dozen or more different dimensional units being used in the technical literature.

As for the conversion, when you determine the liters of solution per mole of solution, just ignore the gas dissolved in the solution ... it will be insignificant when compared to the amount of water. Also, most reported values are based on the grams of water per liter of water at 20 degrees C (i.e., 998 g/L). - mbeychok 20:54, 30 March 2007 (UTC)

I get it now. The aproximation through me off I think. For example:

k=120 mol/kg*bar*(1kg/1000g)*(18g/mole water)*(atm/1.01325 bar)= 2.13 atm and can be used for mole fraction equation as slope for previously mentioned problem. Sometimes those approximation can be difficult. Thanks for the help 70.113.83.253 00:47, 31 March 2007 (UTC)less confused person