[Peter Ridley under another name (OP)]

Rosy thanks fr that help. Ive tried lots of things and nothing worked so will have to do as you said and look for nasty words.

[Peter Ridley under another name (OP)]

Bored chemist I couldn’t find anything about latex dissolving CO2 and mostly its the other way round so are you right about that or just guessing. One site says that the formula for pure latex is C3H3N so as you’re a chemist does that tell you anything about CO2 dissolving in it.

[Peter Ridley under another name (OP)]

A lot of people say on the Internet about their tyres going down when they fill them with CO2 but not with air. Most of them I found are talking about bike tyres like the one I said yesterday http://www.bikeforums.net/archive/index.php/t-154847.html so I did another google and found this http://velonews.competitor.com/2009/02/bikes-and-tech/technical-qa-with-lennard-zinn-large-molecules-and-short-frames_87175. It looks like Glenn who asked the question made the same mistake about the size of CO2 as what Pete Ridley was saying on 14th April about

the paleoclimatologists and their models .. What they do not seem to consider is that it is the kinetic not collision diameter that is appropriate at this stage

http://www.thenakedscientists.com/forum/index.php?topic=38675.0.

Leonard and the

atmospheric chemist/bike nut Alan Hills

on that bike site seem to know about this CO2 leak happening and Alan Hills said

Permeation by diffusion predicts gas leakage rates proportional to the inverse of the square root of their molecular weights. Using air as a reference the predicted leakage rates for common gases are: helium 2.7, air 1.0, nitrogen 1.02, oxygen 0.95, argon 0.85, carbon dioxide 0.81. It turns out however that the leakage rate of CO2 is huge, and the reason is that it is actually soluble in butyl rubber and is thus not constrained to normal permeation loss, it can transfer straight through the bulk rubber resulting in severe tire pressure loss on the order of a single day. .. A reference dealing with CO2 transfer through latex rubber sheds light on the loss process.

That reference he gave is to http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html by Dr. John Christie of La Trobe University in Australia who is

a theoretical chemist, with a particular interest in the development and application of simplistic model theories for chemical problems. My main area of interest is reaction kinetics, mechanism, and energy transfer in reactions.

http://www.latrobe.edu.au/chemistry/people/christie.html.

Dr. Christie sounds as though he is an expert in this so I’ll try to get him to help and let you know what he said or maybe he’ll talk here. I’ll ask him if he’ll help here.

[Peter Ridley under another name (OP)]

Rosy that problem seems to be c h a c h a

[Peter Ridley under another name (OP)]

I’ve E-mailed Dr. Christie and hope that he’ll get back to me but meanwhile I had a good read of what he said about CO2 in bike tyres at http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html. He’s an expert and said

The answer is that the carbon dioxide is much more "soluble" in the rubber that the balloons are made out of. For helium and oxygen, the chains of molecules in the balloon rubber repel the gas molecules, and they have to thread a maze, at best, to escape the balloon

Why did he put the word soluble in those commas as though it wasn’t quite right. Is it dissolving really like things dissolve into water or just going into tiny holes in the balloon and that’s not really dissolving is it?

Then he says about the CO2 having to

thread a maze, at best, to escape the balloon

so that must mean it might be worse than a maize. If you look at those pictures that Pete Ridley talked about on the “Another Hockey Stick Illusion?” thread http://www.thenakedscientists.com/forum/index.php?topic=38675.50 on 27th April at 22:39 in Figure 11 at http://itia.ntua.gr/hsj/45/hysj_45_03_0357.pdf on page 369 especially at the top of the bottom picture it looks like a honeycomb kind of maize for air to get through. Isnt what Dr. Christie says something like what Pete Ridley says is in the ice?

He also said

carbon dioxide is attracted to the chains of rubber molecules, and drawn in between them until it permeates the whole of the rubber. The rubber actually swells in the process. Once that has happened gas molecules can just as easily escape from either side of the balloon, and so the gas is lost relatively fast.

What attracts it to the rubber? And can the same thing happen in the ice that Pete Ridley talks about? As well does the rubber have to swell before the gas escapes? Why can’t gas just keep on going through that maize on the way out to the open air? Won’t the pressure inside the balloon push the gas out instead of letting gas in from the outside.

Any ideas anyone?

I did do a google about Dr. Christie and came across a video “Global Warming: A Scientific and Biblical Expose of Climate Change” http://www.answersingenesis.org/media/video/ondemand/global-warming/global-warming but it was the wrong Dr. Christie. It still has some interesting stuff about climate change especially a graph at 23:30 minutes by a weather man called Mike Oard which shows how temperature change is caused by sunspots not CO2. I might start another question on that one.

Are people here just guessing at what is happening with the CO2, just like Professor Wolff said to Pete Ridley on http://www.thenakedscientists.com/forum/index.php?topic=38675.75   

I think that none of us has a definite molecular-level understanding of the physical process occurring at closeoff, and it would be great if someone can do the experiments in the lab to understand that better

. That’s OK about balloons and contraceptives but not about air and CO2 in bubbles in ice.


I hope that Dr. Christie can be bothered to say something here like I asked him if he would.

[damocles]

Dr John Christie here under a pseudonym (didn't realize that that was what I was setting up when I registered).
I am a "Mad Scientist", not a major expert, but do have some genuine knowledge in this area.

Here is a review article -- not quite on this topic, but it provides a useful clarification of some of the terms that are being used, and a diagram that displays quite clearly three different mechanisms whereby a gas might escape a container.
http://www.benthamscience.com/cheng/samples/cheng%201-1/Sandra%20E.%20Kentish.pdf

In my original MadSci reply at
http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html
--"soluble" was in inverted commas as an implicit warning. I did mean soluble, but people usually think in terms of simple gas in liquid or solid in liquid solutions; solutions in a matrix of rubbery polymer as solvent are more complicated, and do not behave in exactly the same way.
-- "thread a maze, at best" meant exactly what it said. "Thread a maze" is only an option if open microchannels are available -- the first or "Knudsen diffusion" option of the three mentioned in the pdf.

On the underlying topic I have a very firm view that the ice core CO2 record is trustworthy. Regardless of the detail of mechanism or modelling, ANY diffusion process can only move a substance from a region of higher concentration to a region of lower concentration. The fact that sizable fluctuations in ice core CO2 analyses can be seen back to 300kyr or longer is a clear indicator that diffusion over the milennia has been only a minor process. The resolution of ice core analyses is 100-200yr for Vostok and most other cores; 20-30 yr for Law dome:
http://cdiac.ornl.gov/trends/co2/lawdome.html
and google for other refs.

Temporal resolution is a clear indicator of the extent of diffusion, regardless of process.

[Bored chemist]

Bored chemist I couldn’t find anything about latex dissolving CO2 and mostly its the other way round so are you right about that or just guessing. One site says that the formula for pure latex is C3H3N so as you’re a chemist does that tell you anything about CO2 dissolving in it.

As a chemist I know  that formula is just plain wrong. It's close to right for nitrile gloves.
All things dissolve in all other things  to some extent (unless they react).

RD's suggestion will get upset by the CO2 dissolving in the water in the manometer.

[Peter Ridley under another name (OP)]

Hello Dr. Christie thanks very much for commenting here so quickly because ideas from somebody who knows about the processes of molecular movement through pores and channels that approach the size of those molecules is really needed here. You may call yourself a mad scientist but at least you look like you understand the science. I don’t know if anyone else commenting here is a scientist so I think what you say may be more dependable. After all you do have a high qualification and are a science educator. You appear to have knowledge about my question that nobody else here seems to have so please tell me more about how those molecules move through pores and channels that are a similar size to the molecules.

Pete Ridley was asking about the size of molecules and talked about collision diameter being the wrong one and kinetic diameter being the one to use so was he wrong about that? He said that

For many of the gases that make up the atmosphere there is little difference between collision and kinetic diameter, as seen in the listing below, but for CO2 this is not the case. Consequently, as the ice is compressed and pressure builds up in the pockets the CO2 molecules (and any smaller ones) escape from the pockets and move down the pressure gradient towards the surface, long after the larger gases like N2, O2, Ar and CH4 are trapped

http://www.thenakedscientists.com/forum/index.php?topic=38675.0 so that other thing is about a pressure difference. I think he was talking about the air in the bubbles getting squashed and the pressure inside being higher than outside so isn’t that what happens in a balloon and why the gas gets out to the air and not from the air into the balloon?

You also said about

if open microchannels are available -- the first or "Knudsen diffusion" option of the three mentioned in the pdf

I haven’t read the pdf yet but will do next but Pete Ridley also talked about that Knudsen diffusion and said on one of the sites that he linked to that

Some of the pores will be so small that not all of the different types of gas molecules in the air mixture can pass, allowing only the smallest ones through, including CO2, but preventing N2, O2 and CH4. Other pores will be large enough for the whole air mixture to diffuse. I also hypothesise that both Fickian and Knudsen diffusion takes place, depending upon the size of those pores, with Fickian being relevant in the upper layers of firn and Knudsen at the approach to “complete” close-off and a gradual shift in emphasis down the ice sheet

http://www.climateconversation.wordshine.co.nz/2011/03/fallen-snow/ so was he wrong again?

[Peter Ridley under another name (OP)]

Bored chemist you said that the formula for pure latex of C3H3N

is just plain wrong

so can you say what it really is?. You also said

All things dissolve in all other things to some extent (unless they react)

but when I think of something dissolving I think of it going into a liquid and forming ions. I googled “define dissolve” and it said

to  make  a  solution  of,  as  by  mixing  with  a  liquid;  pass  into  solution:  to  dissolve  salt  in  water

(ttp://dictionary.reference.com/browse/dissolve which is how I picture it. I also looked at “define solution” and it said

A homogeneous mixture of two or more substances, which may be solids, liquids, gases, or a combination of these

so it looks I was wrong and solids can dissolve into solids and liquids into liquids and gases into gases and all that so whats the difference between a mixture and a solution? Like the atmosphere is a mixture of different gases but is that a solution or a sponge sucks up water but are they solutions? I didn’t think they were. What makes a solution different from a mixture and how does CO2 going into latex make it a solution? Does the CO2 and latex form a homogenous mixture?

Princeton University says

any combination of two different materials which don't react is a mixture, while solutions are a special kind of mixture where mixing occurs at the molecular level. Thus, all solutions are mixtures, but not all mixtures are solutions. To make the distinction clear, we'll use the phrase "physical mixture" to denote a mixture which is not a solution. So, by this definition, both muddy water and Kool-Aid®  are mixtures of solid and liquid (that's how they're prepared), but only Kool-Aid is a solution

http://www.princeton.edu/~pccm/outreach/scsp/mixturesandsolutions/background.htm. That tells me that if CO2 dissolves in latex then it must react with the latex but does it and if it does why does it come out again by itself.

You also said that

RD's suggestion will get upset by the CO2 dissolving in the water in the manometer

and Ive read that it does do that but it also gets put out by water depending on how hot it is. If there is a full amount of CO2 in the water to start with why would any more dissolve and what would stop some coming out of the water if the temperature went up during the experiment so it could happen either way couldn’t it.

[damocles]

When chemists talk about the shape of molecules, they often get it quite wrong -- including those who write textbooks! Chemists have been in the habit of playing too much with ball-and-stick or wireframe molecular models, and too little with space filling models.

Thus I hear of the CO2 molecule being in the shape of "a needle" in this thread. CO2 is approximately an ellipsoid of rotation, with a long axis around 560 pm and identical short axes around 350 pm. It is thus the shape of an American football, or a peanut. A peanut is a good one because the only way to describe the shape of a water molecule is not a boomerang or a "V-shape", but a cashew nut!

From Yelder

Pete Ridley was asking about the size of molecules and talked about collision diameter being the wrong one and kinetic diameter being the one to use so was he wrong about that?

Collision diameter and kinetic diameter both work out to be an average of sorts between the lengths of the three principal axes. That is, both are strictly larger than the smallest axis and strictly smaller than the longest axis. There is a "fuzziness" of about 10 to 20 pm in the axis length, connected with what one regards as the outer boundary of an atom -- hence the "about" in the football measurements given above. Collision diameter is well defined; kinetic diameter is much more context dependent, and for that reason alone should probably be avoided unless you are reproducing an exact context.

But in this case, if you work along the same lines as the pdf reference, you will realize that there is a lot that does not make much sense. From Pete Ridley:

Some of the pores will be so small that not all of the different types of gas molecules in the air mixture can pass, allowing only the smallest ones through, including CO2, but preventing N2, O2 and CH4. Other pores will be large enough for the whole air mixture to diffuse. I also hypothesise that both Fickian and Knudsen diffusion takes place, depending upon the size of those pores, with Fickian being relevant in the upper layers of firn and Knudsen at the approach to “complete” close-off and a gradual shift in emphasis down the ice sheet

As the pores get smaller, Knudsen diffusion clearly takes over, and the context-dependent kinetic diameter approaches closer to the smaller axis lengths of the molecule. But when the pores reach the size where they start to block the passage of some molecules, I think the view taken in the pdf is the best approach -- the description should be in terms of a different mechanism-- molecular sieving.

However, for the overall discussion purposes, the detail of diffusion mechanism is totally irrelevant! This is the most important point in my previous post. If diffusion of carbon dioxide through ice were a serious problem for the glacial record of past atmospheric CO2, then ice cores would be showing higher carbon dioxide levels, closer to present day levels, and the large variations in the record would be "ironed out" to show a fairly smooth variation. The Vostok record shows anything but that!
http://cdiac.ornl.gov/trends/co2/graphics/vostok.co2.gif

Diffusion can ONLY move material from high concentration to low concentration regions -- 2nd law of thermodynamics. The mechanism of diffusion makes no difference to this, in exactly the same way that scientists can and will rule out perpetual motion machines without looking too closely at the detail of the ingenious mechanisms they are based on.

[Peter Ridley under another name (OP)]

Hello Dr. Christie Ive had a first read of “Carbon Dioxide Separation through Polymeric Membrane Systems for Flue Gas Applications” http://www.benthamscience.com/cheng/samples/cheng%201-1/Sandra%20E.%20Kentish.pdf and was puzzled straight away by the start saying

A developing technology is membrane gas separation, which is more compact, energy efficient and possibly more economical than mature technologies, such as solvent absorption

Is a polymeric membrane like a latex balloon? If it is it seems to say that its not a solvent like water and the CO2 doesn’t dissolve in it so does it dissolve in latex?

The paper talks about molecules adsorbing (I hadn’t heard of that word before) along the pore walls and surface diffusion, not about dissolving in the membrane and that is interesting because Pete Ridley also asked about adsorption. On 28th February at 20:50 he talked about Professor Hartmut Frank saying this happened in the snow as it was falling. He asked Bored chemist

whether or not that initial adsorption of CO2 in the snow is a chemical or a physical process (http://www.tutorvista.com/content/chemistry/chemistry-iv/surface-chemistry/absorption-types.php). My suspicion is that it is Chemisorption but as I’m not a chemist I’d appreciate your opinion. Following on from that is another question about adsorption in the deep firn, but that can be followed up later. Let’s work our way down the ice sheet looking at the different processes that Professor Zbiniew Jaworowski has been expressing concern about since 1992 and return to deep firn adsorption of CO2 and clathrate formation at a later stage

http://www.thenakedscientists.com/forum/index.php?topic=38675.50.

Bored chemist never had a chance to answer that question of Pete Ridley’s about adsorption because the thread was locked. Can you tell me what the answer is please and can you tell me if adsorption occurs in ice not just in snow. I googled adsorption and it says

The accumulation of gases, liquids, or solutes on the surface of a solid or liquid

with a diagram of gas molecules sticking onto charcoal. If CO2 gets adsorbed does it stick to the ice and how thick does it get and does it block up pores and channels or does it go somewhere?

Another thing that paper talks about kinetic diameter like Pete Ridley did. It gives a list of kinetic diameters for N2 O2 CH4 and CO2 in table1 which are nearly like he said on 14th April at 21:38 http://www.thenakedscientists.com/forum/index.php?topic=38675.0.

I’ll have to read the paper again a few times to try to understand more what is being said because its hard for me to understand but I'll keep trying.

[graham.d]

Hi Yelder. I have not read all the posts but it is interesting to see experiments like this being done in a home/kitchen environment. A couple of suggestions to improve the results validity:

1. Use something with better quality control than party balloons. Condoms may be better if rather more expensive.
2. Use several balloons for each single test to minimise the variability of the quality of the balloon and/or method of sealing (knot??) from the experiment.

[damocles]

Hello Dr. Christie Ive had a first read of “Carbon Dioxide Separation through Polymeric Membrane Systems for Flue Gas Applications” http://www.benthamscience.com/cheng/samples/cheng%201-1/Sandra%20E.%20Kentish.pdf and was puzzled straight away by the start saying

A developing technology is membrane gas separation, which is more compact, energy efficient and possibly more economical than mature technologies, such as solvent absorption

Is a polymeric membrane like a latex balloon? If it is it seems to say that its not a solvent like water and the CO2 doesn’t dissolve in it so does it dissolve in latex?

Yes. A latex balloon is acting as a polymeric membrane and selectively passing CO2 in this situation. And the CO2 is definitely dissolving in the latex. It is because it is more latex-soluble than the other gases that CO2 effuses more quickly. Solvent extraction as a  "conventional technology" is quite a different process, involving use of a liquid solvent to selectively remove the gas, followed (if required) by releasing the gas from the liquid again. Physical means like low pressure or warming might be used for this part of the process, or chemical means via reaction. With membrane permeation technology, the required gas dissolves in the membrane, as it would in a liquid solvent, but then it is spontaneously released at the other side of the membrane where there is none of the gas initially present. So the membrane is effectively holding the other gases in and allowing the required gas to escape. The whole situation is governed by the principles of chemical equilibrium-- thoroughly covered in any college freshman course or textbook. Membrane permeation can only separate, never concentrate -- the gas on the extraction side of the membrane arrives at a lower concentration or partial pressure than that in the original sample.

Yelder again:

Bored chemist you said that the formula for pure latex of C3H3N
Quote
is just plain wrong
so can you say what it really is?.

Bored Chemist was quite right about it being the formula of nitrile rubber. Acrylonitrile is CH2=CH-C≡N which is C3H3N. So PAN is {-CH2-CH(CN)-}n , or (C3H3N)n

Latex is {-CH2-C(CH3)=CH-CH2-}n , or (C5H8)n . The lower case n indicates an n-fold repetition, and is nothing to do with the element nitrogen. This sort of thing gives plenty of scope for confusion! There is definitely no nitrogen bonded into a latex polymer.

[Peter Ridley under another name (OP)]

Hello graham.d I was going to get some condoms but then came across those people saying about their bike tyres gong down when CO2 was used but staying up with air so is an experiment needed now to show that it happens. I might get some tyres instead and a bottle of CO2 that they seem to be able to get easily if I want to do it. I’m not sure I need to bother now that Dr Christie is helping on this as he seems to know all about it.

Hello Dr.Christie, thanks for getting back so quickly again. The help that you give is like what Professor Wolff did on the “Another Hockey Stick Illusion?” but more theory like you said you are and he was using the empirical evidence for ice cores. OK so CO2 dissolves in latex and in a polymeric membrane but now you say that it effuses, not diffuses. When I googled effuse I found this “Graham's Law of Effusion” U-tube lesson that says

The rapid and random motion of tiny gas molecules results in effusion, the escape of gas molecules through very small openings

http://www.youtube.com/watch?v=TropqfFqUiI&feature=related and the teacher talks about helium in a balloon and why it goes down

you’ve got it enclosed in a container. Its enclosed in a good balloon usually. Well the holes that it is escaping through may only be about the size of the atoms or molecules that are escaping so the helium can very gradually effuse through

She goes on to say that gases can effuse through bottles. So does that mean that effusion is the same as diffusion but just means going through tiny openings instead of in a big space?

Thanks again for helping because I expect your very busy marking exams or something. That paper you linked to gives a lot of information about the separation of gases from a mixture using a membrane and is a big help but it doesn’t talk about effusion so is it just a matter of people using the words differently. When you say that

the CO2 is .. dissolving in the latex ..  effuses more quickly .. but then it is spontaneously released at the other side of the membrane

would someone else say it effuses more quickly through it? I’m still puzzled about that word dissolve so Ill give an example of what I didn’t think was dissolve. A sponge has lots of little holes and water can go into those holes so there is a mixture of a liquid in a porous flexible solid but is the water dissolved in the sponge? I didn’t think so. Whats the difference between a very thin sponge and a latex or polymeric membrane?

[damocles]

Yelder, a response to a couple of points in your latest.

Effusion and diffusion? It is all a matter of Latin prefixes. E(f)-fusion is out of -melting, and di(f)-fusion is through-melting. So diffusion refers to something moving through a matrix of some sort, and effusion refers to something moving out of a container. They are really the same process (or set of processes). But to say "diffusion through" or "effusion out of" is a tautology (redundancy), while to say "diffusion out of" or "effusion through" may be valid, but is more likely a mild oxymoron (contradiction).

Solutions and mixtures and holes in sponges and the like? The word dissolve relates very directly to solutions and the process of entering into a solution. These are very basic concepts in Chemistry, and probably should be discussed a little more and in more depth in chemistry subjects at secondary and tertiary level. The key concept is a matter of homogeneous or heterogeneous. In a true solution, the component substances are divided at molecular level, and any sample of about 1000 molecules or more should have the same molecular make-up with only statistical variation. In a heterogeneous mixture the divisions are "lumpy" with clumps of many molecules of each of the component substances. There is also a very important intermediate grey area with mixtures known as colloids, where the components come in lumps of size about 1 nm to 1 μm (one millionth to one thousandth of a millimetre). Bigger than single molecules, but not much bigger! Colloids have some interesting and surprising properties. Thirty or forty years ago colloid chemistry was a bit of a backwater specialization. More recently it has formed much of the basis of the modern and trendy field known as nanotechnology.

And I am not really busy marking exam papers and the like; I am enjoying a very relaxed retirement. I maintain an Honorary appointment to my Department for the small amount of professional work I might get around to doing!

[Bored chemist]

Effusion is the word usually used to describe a gas escaping through a small hole- for example a pinhole in a piece of metal foil.
Diffusion is the transfer of a material through the bulk of another material.
I can calculate effusion rates directly from the kinetic theory of gases (though I'd not like to have to- it's been a while since I studied that).
Diffusion rates are measured empirically because they depend on a lot of odd parameters. The exception is the diffusion of one gas through another (for example when you smell a gas leak)  which you can calculate, and even that case is fairly complicated.

[Peter Ridley under another name (OP)]

Dr. Christie thanks for helping me on what diffusion is which I now think I understand better but not all except the bit about melting but I guess that is just the Latin and I neednt worry about it. You said

So diffusion refers to something moving through a matrix of some sort, and effusion refers to something moving out of a container

Thinking about that balloon or tyre isnt the rubber a “matrix of some sort” so is the He or CO2 doing effusion and diffusion at the same time?

I remember on the “Another Hockey Stick Illusion?” http://www.thenakedscientists.com/forum/index.php?topic=38675.25 on 19th April 04:02) yor_on quoted from “Carbon dioxide concentrations for the Last Millennium, Antarctica” http://doi.pangaea.de/10.1594/PANGAEA.728135 about

diffusion of dissolved air through the ice matrix into the bubbles

then Pete Ridley said on 28th April at 20:50 what Professor Hartmut Frank said about

preferred diffusion of CO2 into the ice matrix

http://www.thenakedscientists.com/forum/index.php?topic=38675.50. Then Bored Chemist said here on 31st May at 09:46

the gases .. can "dissolve" in the rubber, diffuse through it, and escape. Secondly the air outside a balloon full of CO2 will diffuse into the balloon .. so the balloon is filling up as well as emptying

http://www.thenakedscientists.com/forum/index.php?topic=39542.0.

You linked to a paper in your first comment here and it says in section 2.2 about

The molecular sieve framework forms a well-defined repeating structure of regular channels and cages. Gas separation is dependent on the size of these channels and cages relative to the kinetic diameter of the gas. The difference in kinetic diameter of gas molecules (Table 1) dictates which molecular sieves are useful and provides an indication of selectivity [17]. For example, Zeolite 3A separates hydrogen effectively from hydrocarbon feeds because the pore diameters are ~3 Å [109]. Zeolite 4A has pore sizes of ~ 4 Å, which will separate carbon dioxide from nitrogen and methane

http://www.benthamscience.com/cheng/samples/cheng%201-1/Sandra%20E.%20Kentish.pdf. It also shows a picture in fig (6) of what happens.

I see the “porous hollow fibre” like a container and the wall like the membrane of a balloon or tyre with a “repeating structure of regular channels and cages” to be a matrix so does that mean that the hydrogen and carbon dioxide are dissolved into the membrane then diffuse through it and effuse out of it? Like you said

They are really the same process (or set of processes)

On that business about what was right to use kinetic or collision diameter am I right to take what Pete Ridley said that it is kinetic diameter when those “regular channels” are around the size of the molecules “~3 Å” and “~ 4 Å”? I’d like to be able to clear that one up before talking about the other things in that paper “Carbon Dioxide Separation through Polymeric Membrane Systems” like the different ways to separate gases. It says

There are five possible mechanisms for membrane separation .. Knudson diffusion, molecular sieving, solution-diffusion separation, surface diffusion and capillary condensation .. Molecular sieving and solution diffusion are the main mechanisms for nearly all gas separating membranes. Knudson separation is based on gas molecules passing through membrane pores small enough to prevent bulk diffusion ..

 
You’ve said a little bit about Knudsen diffusion and molecular sieving but I think Ill have more questions if you have time to keep on helping me.

[Peter Ridley under another name (OP)]

Hello again Dr. Christie, on this thing about CO2 inside a balloon dissolving into the latex then diffusing then effusing into the air I had another read of your answer to “Why is my carbon dioxide effusing too fast?” http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html and see you said then that

'The permeation of small molecules through flawless polymer films occurs by the consecutive steps of solution of permeant in the polymer and diffusion of the dissolved permeant.' In the table for Natural rubber which follows (page III-233), the following permeabilities are given: oxygen 23.3, argon 22.8, nitrogen 9.43, carbon dioxide 153. Permeability is governed by solubility and diffusion. There is little difference in the respective diffusion coefficients: 1.73, 1.36, 1.17, and 1.25 for the four gases (note that diffusion coefficients through the polymer do not reflect either molecular size or molar mass directly). The striking difference in the permeability figure for carbon dioxide is associated with solubility in the rubber: heat of solution figures are -4.2 kJ/mol for oxygen, -0.1 for argon, +2.1 for nitrogen, but -12.5 for carbon dioxide

That seems to answer part of what I asked in my last comment about 

so does that mean that the hydrogen and carbon dioxide are dissolved into the membrane then diffuse through it and effuse out of it?

except for the effuse bit. I see that CO2 permeability is 6 times for O2 and Ar and 15 times N2 so does the same thing happen  in ice? Am I right thinking that the – “heat of solution” figures for O2 Ar and CO2 mean that heat is generated not used http://www.google.co.uk/search?q=define+%22heat+of+solution%22&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-GB:official&client=firefox-a#hl=en&client=firefox-a&hs=rU1&rls=org.mozilla:en-GB:official&q=Heat+of+solution&tbs=dfn:1&tbo=u&sa=X&ei=BDHtTdD0Cc_C8QPDtJTDAQ&ved=0CBgQkQ4&bav=on.2,or.r_gc.r_pw.&fp=11e1338e32ed5bc&biw=1024&bih=535? If it is could that make ice melt a bit?

I googled - permeability CO2 ice – and found a 1958 paper “Permeation of Gases through Ice” http://onlinelibrary.wiley.com/doi/10.1111/j.2153-3490.1959.tb00041.x/pdf that said

One may think of two possible pathways for the permeation of gas through ice, either through pores in a dry crystalline ice structure, or through a liquid phase which might exist in the ice. In the first case, according to Graham's law, one would expect that the smaller oxygen molecules would move through the ice in greater amount than the carbon dioxide molecules, but if permeation takes place through liquid pathways carbon dioxide would pass through in greater amount because of its 20 -30 times greater solubility. The latter was clearly the case, and this strongly suggests that we are dealing with permeation through a liquid phase

I see that he says

the smaller oxygen .. than the carbon dioxide molecules

then says that is why CO2 is more permeable because of liquid being there. If kinetic diameter should be used for the permeation would there need to be liquid for CO2 to permeate more easily and if liquid is there would the CO2 permeate even more easily and would it make more liquid because of “heat of solution” do you think? 

[damocles]

Just a quick comment on a couple of points from Yelder's latest:

Am I right thinking that the – “heat of solution” figures for O2 Ar and CO2 mean that heat is generated not used

This is quite right. However the heat is associated with entering into solution or leaving solution. If a gas is dissolving into a membrane, there will be a minute heating of the entry side and a minute cooling of a little under the same size at the exit side.
A brief technical lesson: The solubility of a material is governed by the "standard free energy of solution". This has two components, one of which is the "heat of solution" or "standard enthalpy of solution" that I quoted. The other is an entropy based term. For solid in liquid solutions, this can vary a lot.  But it is usually a large positive entropy, as the relatively ordered structure of a solid is broken down into a less ordered random distribution in a liquid solvent. But for solutions of gases it is a small negative entropy that varies little for different gases or different solvents. Gases are slightly less disordered in solutions than as the free gas because their motions are somewhat restricted. So my reason for quoting "heats of solution" was because it gives a strong indication of the affinity of the gas for the matrix, and of the consequent solubility. It was not really anything to do with heat as such.

I googled - permeability CO2 ice – and found a 1958 paper “Permeation of Gases through Ice” http://onlinelibrary.wiley.com/doi/10.1111/j.2153-3490.1959.tb00041.x/pdf that said
Quote
One may think of two possible pathways for the permeation of gas through ice, either through pores in a dry crystalline ice structure, or through a liquid phase which might exist in the ice. In the first case, according to Graham's law, one would expect that the smaller oxygen molecules would move through the ice in greater amount than the carbon dioxide molecules, but if permeation takes place through liquid pathways carbon dioxide would pass through in greater amount because of its 20 -30 times greater solubility. The latter was clearly the case, and this strongly suggests that we are dealing with permeation through a liquid phase
I see that he says
Quote
the smaller oxygen .. than the carbon dioxide molecules
then says that is why CO2 is more permeable because of liquid being there. If kinetic diameter should be used for the permeation would there need to be liquid for CO2 to permeate more easily and if liquid is there would the CO2 permeate even more easily and would it make more liquid because of “heat of solution” do you think? 

It is important to understand the context of this paper. It is written by a biologist whose reason for pursuing this enquiry has to do with the survival of plants through the Canadian winter. He is actually doing the experimental work at temperatures that are not extreme -- just a few degrees below freezing.
You have been contending that kinetic diameter of CO2 is smaller than that of O2 or N2, and that kinetic diameter rather than collision diameter should be used in these diffusion studies. If you are right, then his conclusion (that liquid brine channels must be an important factor) is invalidated.

If kinetic diameter should be used for the permeation would there need to be liquid for CO2 to permeate more easily and if liquid is there would the CO2 permeate even more easily and would it make more liquid because of “heat of solution” do you think?

(Hope it is not bad form to re-quote) Let us get the logic of this into place. He has MEASURED diffusion rates, and INFERRED that liquid channels must be involved to explain why CO2 diffuses faster than O2. If you are right and he is wrong about the diffusion treatment in the absence of liquid channels, then that undermines his INFERENCE but has absolutely no effect on his MEASUREMENTS. There is no question of CO2 permeating even more easily, and as explained above, release of "heat of solution" in this context is not enough to melt anything.

His study makes some other telling points:
-- that the rate of diffusion of all three gases is more than a million times slower in ice than in water,
-- that diffusion rates fall off rapidly with decreasing temperature (though he only explores temperatures relatively close to melting point, so this trend might not continue).

[Peter Ridley under another name (OP)]

Hi Bored chemist, in your last comment you said

Effusion is the word usually used to describe a gas escaping through a small hole- for example a pinhole in a piece of metal foil

I think that one of the difficulties that many of us lay people have is the different way that people, even scientists, use the terminology. Elsewhere effusion is described as you did but with the rider “into a vacuum” (although one source said “Effusion is the escape of a gas through a small hole into a vacuum or area of lower pressure”). Pete Ridley gave a link http://www.thenakedscientists.com/forum/index.php?topic=38675.0 14th April at 09:36) to an animation http://www.youtube.com/watch?v=0uBK7VxT00E that does that and describes how to

calculate effusion rates directly from the kinetic theory of gases

so it might help jog your memory.

Pete Ridley went on to say

but imagine that the bubble is an air pocket in an ice sheet approaching close-off, with all excepting one pore closed to all molecules (CO2 included). Imagine also that the hole size of that single pore is just larger than 0.33nm (the kinetic diameter of CO2) and that the red balls are CO2 molecules (N2, O2 and CH4 molecules present but not shown because they can’t escape but are still bouncing around inside in far larger quantities than CO2). Also imagine that the pore is not giving access to an empty space as shown but access to an equally small channel linking to another similar air pocket in a chain of such air pockets. Does that very simplified picture of the structure within the ice/firn help to clarify the basis of my main question? Does that very simplified picture of the structure within the firn/ice help to clarify the basis of my main question?

.

I see that you didn’t offer any help about this on that thread which is a shame because he needed it. Let’s hope that he’s watching this one and learning from it like I am.

Dr Christie’s explanation on 4th June at 00:29, involving going back to the Latin origin then talking about

The key concept is a matter of homogeneous or heterogeneous. In a true solution, the component substances are divided at molecular level

has helped me understand this a lot better but perhaps not fully. My understanding of the terms dissolve, diffuse and effuse were much too restricted. What I now understand the different terms to mean are:
- “to dissolve” is to form a homogenous mixture of several different substances,
- “to diffuse” is to move within (a vacuum, a fluid, a solid),
- “to effuse” is to move out of (a vacuum, a fluid, a solid),
(is another term “to infuse”, meaning to move into (a vacuum, a fluid, a solid) is required?)
In the context of this discussion we are specifically talking about individual molecules.

You said

Diffusion is the transfer of a material through the bulk of another material

and I see the significant word there being “bulk”. Dr. Christie said

diffusion refers to something moving through a matrix of some sort

and that puzzles me. From the definitions that I use above water going into a sponge and being squeezed out again is not dissolving (infusion?), diffusion and effusion because the substance of the sponge is not present as free molecules. Both water and sponge are “material” (per your definition of diffusion), the water is “something” and the sponge is “ a matrix of some sort” (per Dr. Christie’s definition). Despite that I do not think that water that has entered, permeated and been squeezed from a sponge has dissolved (infused?) diffused and effused because it does not form a homogenous mixture at the MOLECULAR level.

If my understanding is flawed again then please put me straight.

If I understand correctly then can you explain the difference between a balloon that has been punctured with numerous tiny holes (let’s say 10nm diameter each) and one that naturally has numerous tiny pores (let's say 0.33nm) as a result of being blown up and the latex stretched? Michegan State University Chemistry Department provides a spacefill model (which you can zoom into) of the molecular structure of latex [urlhttp://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/lipidstr2.htm#rubber/url]. This tells me that there are tiny air spaces between the fabric (a matrix of C and H atoms? With no mention of anything else, like water) which must grow larger as the fabric is stretched (as in blowing up a balloon). At some stage the spaces must become large enough to let through any trapped gas inside, like He or CO2. Is that what you and Dr. Christie are referring to as dissolving, diffusing and effusing into the outside air? If so, what is the appropriate measure of the gas molecules size when the air holes in the fabric are large enough for them to escape?

When I googled –effusion "into a vacuum" video – I came across “Chemistry: Effusion and Diffusion” http://thinkwell.mindbites.com/lesson/4721-chemistry-effusion-and-diffusion, part of a series of Chemistry course lectures taught by Professors Harman, Yee, and Sammakia available from Thinkwell, Inc. http://www.thinkwell.com/student/product/chemistry. The scientist presenting the lecture starts off talking about effusion being gases moving through a pin hole into an evacuated space and Graham’s Law. I was getting all excited – then it stopped and asked for $2.97 to see the rest.

You also said

Diffusion rates are measured empirically because they depend on a lot of odd parameters. The exception is the diffusion of one gas through another .. which you can calculate, and even that case is fairly complicated

Dr. Christie agrees with you about the complexity of this subject and as Professor Wolff said on "Another Hockey Stick Illusion?" about the processes in the deep firn of an ice sheet

I think that none of us has a definite molecular-level understanding of the physical process occurring at closeoff, and it would be great if someone can do the experiments in the lab to understand that better.  But it won't alter the empirical facts[/quote http://www.thenakedscientists.com/forum/index.php?topic=38675.75.