# Talk:Raoult's law

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## Deviations from Raoult's Law

Can someone provide information on how activity coefficients demonstrate either positive or negative deviations from Raoult's Law? 171.64.133.56 22:53, 24 February 2006 (UTC)

Henry's law is actually the relation between partial pressure of the gases and the solubility of the gases at a given temperature. It defines that the solubility of a gas is directly proportional to the partial pressure of the gas. If we remove the proportionality sign then we insert a constant that constant is called the Henry's law constant.

### Ternary systems vapour pressures deviation

Hi! I've noticed your background and edits on the topics concerning thermodinamics. In this context I request some feedback from you regarding the deviation from the ideal Raoult's law in ternary mixtures in order to fill in the article in this respect.

The article mentions positive and negative deviation in binary sistems. What could happen if a positive deviation binary mixture is mixed with a negative one? Could (it be that) they cancel out their deviation from ideality and the resulting mixture be an ideal one? Do you know some sources regarding this aspect?--188.26.22.131 (talk) 08:39, 15 July 2013 (UTC)

I have no sources but intuitively I would expect a partial cancellation. If for example A-B has positive deviations and A-C has negative deviations, then a molecule of A is attracted more weakly to B molecules than to other A molecules, and more strongly to C molecules than to other A molecules. So in a ternary mixture the average forces on an A molecule should be intermediate between those in A-B mixtures (with the same amount of B as in the ternary mixture) and A-C mixtures. And therefore the vapour pressure should also be intermediate. However I think we need some sources to check my reasoning before actually inserting this in the article - try either advanced textbooks or a Google search. Dirac66 (talk) 19:08, 15 July 2013 (UTC)
Of course some sources must be checked before insertion in article. What advanced sources come in your mind? Useful in this context would be a browsing of ternary azeotropes databases, if there are some.--188.26.22.131 (talk) 09:59, 17 July 2013 (UTC)
As I said, I unfortunately have no sources. If you can find useful information in azeotrope databases, that might be helpful. Dirac66 (talk) 01:52, 18 July 2013 (UTC)

This article needs a lead paragraph that introduces the subject, any practical "real world" applications and does so in layman's terms before launching into the technical explanation. Anyone want to try? --Monotonehell 04:11, 17 March 2007 (UTC)

## application of raoult`s law

applications of rault`s law may be found as colligative properties.root cause of all such properties is vapor pressure which is explained in Raoult`s law

## proof of roult's law

What is the proof of the law that vapour pressure of a component of a solution is V.P. of its pure form multiplied by its mole fraction in the solution? —Preceding unsigned comment added by 121.247.78.162 (talk) 05:29, 11 October 2009 (UTC)

## Positive deviation diagram is incorrect???

Should there not be a green curve, as in the negative deviation diagram but, bulging upwards that sums up the individual vapor pressures? LoneSeeker (talk) 16:12, 30 December 2009 (UTC)

## Diagrams should be more general

All three diagrams (ideal and non-ideal) assume that the vapour pressures of the two pure components are equal: pA* = pB*, so that the total vapour pressure is independent of the mole fraction and is represented as a horizontal line. However this is only a special case - in general this assumption is not true and the total vapour pressure line should have a non-zero slope. More general diagrams can be found in most general chemistry and physical chemistry texts. Dirac66 (talk) 17:42, 9 November 2010 (UTC)

Done. I have now replaced these diagrams with new diagrams for which the Raoult's law total vapor pressure has a non-zero slope. The new diagrams are copied from the Italian Wikipedia and I have re-captioned them in English. Dirac66 (talk) 01:07, 27 May 2012 (UTC)

## Electrolytes

The statement for electrolytes should be added.--82.137.12.0 (talk) 23:32, 9 August 2012 (UTC)

## Notation for fugacity coefficient

brought from User talk:Petergans#Raoult's law:

Hi - could you glance at the latest edit of Raoult's law by 5.15.206.167? It seems confusing to me to use the same symbol for gas-phase fugacity coefficient and liquid-phase activity coefficient, but I am wondering if that is common in solution thermodynamics? Dirac66 (talk) 20:34, 23 May 2013 (UTC)

This article is a mess. It is written (badly!) in the style of "Wikipedia for Dummies". I suppose that because this topic is often taught at children there has to be some dumbing down, at least initially. I hate it when dumbing down means making erroneous statements. In this case, deviations from ideality are not just due to enthalpy effects (implied by talking about intermolecular forces); space-filling factors (entropy) also come into it. Deviations from ideality cannot be discussed at an elementary level.
My suggestion would be to separate the description of the law and deviations from ideality from the quantitative thermodynamics. Certainly fugacity, which has the dimension of pressure, and liquid-phase activity coefficients, which have no dimension, should be clearly distinguished from each other. According to Atkins, fugacity coefficient is given the symbol Φ, not γ. Petergans (talk) 07:32, 24 May 2013 (UTC)
Yes, I suppose you are right. I was not really looking at the article as a whole, but it does need extensive revision and should be reordered with the more elementary material first. And it should be done with extensive consultation of sources to ensure it is correct, as we did for the spectroscopy articles. I am not sure, though, that referring to intermolecular forces always implies that entropy effects are excluded. This is true if we consider only regular solutions, but stronger forces can produce ordering in solution.
Anyway, proper revision of this article would take more effort than I am willing to expend, so I have decided not to attempt it at least for now. Thanks for the discussion. Dirac66 (talk) 00:36, 25 May 2013 (UTC)

Hello wikifellows!

I've noticed the comments regarding the symbol of the coeficient of fugacity. I think that some details about the reasons for choosing a very similar notation are necessary.

Choosing the same letter and a subscript for distinguishing them is based on the need for notational uniformity requested by symbol overlaping which could appear in a broader context (for instance phi for fugacity coefficient, osmotic coefficient and volume fraction to mention just a letter which is involved in this discution).

The same letter also emphasizes the connexion between the two concepts and avoids the unnecesary overlap with distinct concepts like volume fraction. The subscript p comes from considering the fugacity coefficient as an activity coefficient in pressure like those based on dimensional expressions of compositions like gamma-c and gamma-b.

From the reasons shown above I suppose it is obvious that the chosen letter seems to be appropiate for the intended use.

A question arises in this context: On what is the statement concerning elementary non-approachability of the deviation from ideality based?--5.15.200.9 (talk) 21:57, 10 July 2013 (UTC) — Preceding unsigned comment added by 188.26.22.131 (talk)

Well, the article does clearly distinguish between gamma-p,i and gamma-i so I suppose that is clear enough. There was also a gamma with no index in the text, which I have now changed to gamma-i to agree with the equation.
As for the statement on "elementary non-approachability of the deviation from ideality", I cannot determine which statement you mean. Could you please copy and paste here the exact statement for which you would like an explanation? Dirac66 (talk) 23:23, 15 July 2013 (UTC)
User Petergans said above "Deviations from ideality cannot be discussed at an elementary level". This statement requires some clarification. What are the factors that might get in the way of an elementary level presentation/discution of the deviation from ideality of the mixtures?--5.15.206.173 (talk) 14:44, 16 July 2013 (UTC)