Is pressure equalization "diffusion"?

There is another question on the site which is:

Two containers, A and B, connected by a closed valve were evacuated and the Chlorine gas (Cl2) with a pressure of 200kPa was put into A and Oxygen (O2) with a pressure of 150kPa into B. a)If Container A has a volume of 10L and container B has a volume of 5L, find the total pressure within the system if the valve were opened and the gases allowed to mix b)Which of the gases would diffuse through the valve at a faster rate?

It has been a long time since I took chemistry and blundering around with Google didn't really seem to answer my question about a technical point about question (b) for this problem.

Obviously when you first open the valve between containers A and B the pressure is going to equalize. Since A has a higher pressure, gas will flow from A into B. Is this diffusion?

In a weird way the pressure equalization does fit the basic notion of diffusion - molecules mover from an area of higher concentration to an area of lower concentration. Thus if both containers had oxygen, then container A would be more concentrated (e.g mol $\rm L^{-1}$) since it has a higher pressure. Thus the molecules will move from A to B because there is a lower "concentration." However this doesn't really seem to fit my notion of either diffusion or effusion. So is there a better proper term for this or is the phrase "pressure equalization" about as good as can be done? Or am I just wrong?

Obviously after the pressures equalize, then the oxygen from the oxygen/chlorine mixture will diffuse into the chlorine faster since oxygen molecules have a lower mass.

The gist is that the question would be simple to answer if containers A and B had the same pressure. But the difference in pressure seems to make the question turn on a very exacting definition of diffusion.

Answer

Its not diffusion, it's effusion. The difference is that with diffusion the particles/molecules are migrating through a permeable medium where as for effusion the particles/molecules are migrating through a pore/hole.

For example, a scent travelling across a room is diffuision, a scent from the room traveling outside is effusion. Also fun fact: the helium escaping through a balloon skin is actually effusion not diffusion.

helpful source

Side note: I am starting to flashback to all the times my thermo professors said diffusion when they meant effusion.

organic chemistry - Regioselectivity in iodolactonisation of γ,δ-unsaturated carboxylic acid

In the last step of the iodolactonisation of 3,3-dimethylpent-4-enoic acid,^[1,2] why does the carboxylate attack the iodonium to form a 5-membered ring, when a more stable 6-membered ring is possible? Both of the sites seem to be equally favorable sterically. I can't come up with a reason favoring the formation of the 5-membered ring.

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References

1. 
   
   

   Takano, S.; Sato, N.; Akiyama, M.; Ogasawara, K. A Synthesis of trans- and cis-Caronaldehydes. Heterocycles 1985, 23 (11), 2859–2872. DOI: 10.3987/R-1985-11-2859.

   
   


2. 
   

   Ding, Y.; Jiang, X. A Novel Highly Stereoselective Synthesis of the A-Ring of Taxol Via Two Aldol Reactions. J. Chem. Soc., Chem. Commun. 1995, 1693 DOI: 10.1039/C39950001693.

   
   

Answer

There are several arguments. Firstly, five-membered ring formation is generally kinetically more favourable than 6-membered ring formation. As ring size increases, the entropy of activation also increases – this is explained in greater detail in Clayden 2ed, pp 805–807. It is true that six-membered rings are less strained, but that is generally more of a thermodynamic consideration, and from a kinetic point of view the entropy factor happens to outweigh the enthalpy factor.

Secondly, for cationic ring-opening reactions (e.g. reactions of halonium ions, or epoxide opening under acidic conditions), it is usually the more substituted end that preferentially reacts. See e.g. Regioselectivity of bromination of alkenes. This is also explained in Clayden 2ed, pp 436–438.

However, probably the most relevant factor here is stereoelectronic in nature. Stereoelectronic effects refer to effects which depend on the spatial orientation ("stereo") of orbitals ("electronics"). In the case of an S_N2 reaction, the key requirement is that the lone pair of the nucleophile (Nu) must be able to reach the σ* orbital of the C–X bond being broken. Since the σ* orbital points out of carbon diametrically opposite the leaving group X, this is equivalent to saying that we need a collinear Nu···C···X geometry in the transition state.

For ring-forming reactions, there are a set of guidelines – Baldwin's rules – which empirically describe whether these reactions are stereoelectronically favoured (i.e. whether the nucleophile and electrophile are capable of orienting themselves in a geometry that allows for reaction). In the case of six-membered ring formation via substitution at a tetrahedral carbon, the reactions are labelled 6-exo-tet or 6-endo-tet depending on whether the leaving group X is outside the 6-membered ring (exo), or inside the ring (endo). [Technically, 6-endo-tet reactions are not ring forming.]

It turns out that although 6-exo-tet reactions are perfectly OK, 6-endo-tet reactions simply do not happen, as the nucleophile cannot stretch itself to reach the C–X σ*.

The opening of a three-membered ring is somewhat intermediate between these two cases. Because the C–X bond is constrained in a small ring, the reaction leans towards being a disfavoured 6-endo-tet reaction, even though formally it is 6-exo (as the leaving group is outside the ring being formed):

The lack of overlap isn't obvious from the 2D diagrams here, but bear in mind that these compounds are not flat – especially in the case of the epoxide, where if the epoxide is in the plane of the paper, the alkyl substituent must be pointing up towards us (or down away from us).

As a result of this, ring opening of the iodonium ion to give a five-membered ring is much more favourable.

A similar example is seen in acid-catalysed epoxide opening.^[1,2] The formation of the 6-membered ring (the tetrahydropyran) is not observed at all:

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References

1. Janda, K.; Shevlin, C.; Lerner, R. Antibody catalysis of a disfavored chemical transformation. Science 1993, 259 (5094), 490–493 DOI: 10.1126/science.8424171.


2. Na, J.; Houk, K. N.; Shevlin, C. G.; Janda, K. D.; Lerner, R. A. The energetic advantage of 5-exo versus 6-endo epoxide openings: a preference overwhelmed by antibody catalysis. J. Am. Chem. Soc. 1993, 115 (18), 8453–8454. DOI: 10.1021/ja00071a067.

sources mekorot - What is déjà vu?

Déjà vu is the strong feeling that one has already experienced a particular situation, while that situation is occurring. Theories abound as regards what it is, what causes it and what possible connection (if any) it might have to mental illness (see here, for a small range of opinions). It may be that everybody experiences it, even if only extremely rarely, and there is no reason to suppose that it is at all a new phenomenon.

My question is, are there any references to déjà vu (to what we might now call déjà vu) in the rabbinic literature? Anything from the Talmud, the midrashim, the literature of the geonim, etc, from which one could construct a Jewish perspective on what déjà vu is? Or anything concerning whether or not it possesses any spiritual significance?

halacha - Is it possible that Judaism would one day allow eating pork?

As far as I understand, pork was originally banned from consumption since it was hard to maintain a clean enviroment for pigs in a desert climate (as summarized in the Wikipedia).

Since nowadays there is a much better understanding of how diseases transmit and modern technology for keeping animals healthy and clean, is it possible that pork would be allowed for consumption sometime in the future?

Answer

No, pigs will not be kosher food, not even when pigs learn to fly -- well, at least not until the Messiah comes or science finds a way to change the pig from a pig into something else a bit different.

The Torah prohibits animals that can be eaten based on physical characteristics. Leviticus 11:1-32. A kosher animal among mammals must have a cloven hoof and chew its cud. Lev. 11:3. The Torah goes on to give us examples: a camel, a badger, and a hare are forbidden because they chew their cuds, but do not have a cloven hooves. Lev. 11:4-6. The swine is given as the opposite case because it has a parted hoof but does not chew its cud. Lev. 11:7. The Torah gives us no other reason, certainly no health reasons. And I am unaware of any health reasons that make it unsafe to eat camels, badgers or hares.

Moreover, it is not within our authority to change the Law if we wanted to. Deut. 4:2 states that we can neither add nor subtract to the Torah.

The story could change when the Messiah comes and as for that there is some dispute. The midrash on Lev. 11:says that the reason that the pig is called “chazir” is because in the future Hashem will return (lehachzir) the pig to Bnei Yisrael and permit it to be eaten. According to many Achronim the midrash is to be taken literally; pig will be kosher in the future. The Rama Mipano (Asarah Mamaros Chikor Hadin 4:13) explains that Hashem will make the pig chew its cud, thereby making it kosher. Critics of this point, however, argue that there is a rigid guideline that prevents this, citing the Gemara at Bechoros 5b, “hayotzei min hatamei, tamei – anything that comes from a non-kosher animal is not kosher.” Therefore if a non-kosher animal gives birth to a kosher animal (which has the kosher signs), it is forbidden to be eaten.

According to Rabbi Raphael Fuchs, Rambam (Maimonedes) would say that a genetically-engineered pig that chews its cud would also be prohibited because it is not one of the ten explicitly-permitted animals mentioned in the Torah. Hilchos Machalos Asuros 2:3. Any other animal (even if it has the kosher signs) is prohibited to be eaten because it is a lav haba michlal assei (when the Torah says you should do this it is inferred that it is prohibited to do otherwise – and the Torah says to eat these animals). It is for this reason that humans are prohibited to be eaten, since they are not one of the animals explicitly mentioned in the pasuk. However, if you hold that way it would seem to me that you also can't eat turkey because it is not mentioned in the Torah.

So, how do we explain the midrash? The Radvaz (Teshuvos 2:828) explains that the midrash is not to be taken literally; rather it should be understood that in the future Bnei Yisrael will eat mashmanim, as if eating pig was permissible. Rabbeinu Bichaiya also explains that the intention of the midrash was not to say that pig will become permitted for consumption in the future, but rather that the midrash is referring to the kingdom of Edom (which is referred to as the chazir) – that Hashem will eventually return (lehachzir) on them midas hadin (judgment). The Ritva (Kiddushin 49b) explains that the midrash is referring to Amalek.

There are opinions that suggest that a genetically-engineered pig (made with kosher signs) could be kosher if it was born of another genetically-engineered pig. This assumes the rabbinic principal that something born of a forbidden item cannot become permitted. Menachos 21a (example, boiled animal blood would technically be kosher according to the Torah, but since blood in its natural state is forbidden, rabbinically, we can not eat boiled blood, either). But once genetically-engineered pigs are born, they would become permitted to be parents of kosher little pigs. See this article from the Jewish Press.

tefilla - Standing during pesukei d'zimrah

What is/are the earliest origins of the customs to stand during various passages of the daily service before the Amidah (e.g. Baruch She'amar, Shirat Yam, Yishtabach)?

grammar - When is よう written in kanji as 様?

We have been taught a lot of uses of よう pattern like ように, Vます ように, sentence ending with ように, ようだ for comparison, etc. But everywhere in textbooks, the よう is written in hiragana. I recently found out that よう actually has a kanji 様. On checking jisho.org, I found that

様 よう
1: (Usually written using kana alone) (usu. after the -masu stem of a verb) appearing ...; looking ...;
2: (usu. after the -masu stem of a verb) way to ...; method of ...ing;
3: (usu. after a noun) form; style; design;
4: (usu. after a noun) like; similar to; (Noun) thing (thought or spoken)

So according to them, the only time it is written in hiragana is when よう follows the ます形. However my (non-native) teacher says it is always written in hiragana when it is used as a grammar pattern. As a result, I am pretty much confused how it is written.

I have read istrasci's answer to the question When should I replace kanji with hiragana, where he mentions that when writing elementary books, kanjis are often intentionally written in hiragana, since children can't recognize them that easily. Is this a possible reason why よう is written in hiragana or is よう really written always in hiragana when using as grammar pattern? If it is at all written in kanji, how to distinguish those cases?

On a side note, many words are written specifically in hiragana when used for grammatical purposes. In such cases, what impression do I give to the reader if I write those words (unknowingly) in kanji?

Answer

This depends on personal taste and situations, but in general Japanese people are generally taught to use hiragana for auxiliary verbs and particles.

• ～あての(手紙)　～宛ての(手紙)　(a letter) to ～


• ～ごとに　～毎に　per ～


• ～ために　～為に　in order to ～


• ～できる　～出来る　be able to ～


• ～ように　～様に　like ～



• ～において　～に於いて　at ～ (place)

I suppose many Japanese style guidelines (for newspapers, official documents, and such) have explicit rules to avoid kanji in those cases.

Those were frequently written in kanji before WWII, and people can still read and understand the kanji versions without difficulty. A few occasions of the kanji versions should not be frowned upon too much. However, excessive use of kanji for those cases can make you look like simulating old documents, or simply less trained to write modern formal Japanese.

I'm not quite sure, but according to my J->E dictionary, "stilted", "pompous" and "bombastic" may be the words I can use to describe my impression of the kanji versions.

Does もあれば have set phrases?

I came across a sentence using もあれば where there wasn't a conditional. あれば got translated as sometimes:

名詞から動詞が派生していることもあれば、その逆のこともある。
Sometimes a verb is derived from a noun and sometimes it is the other way around.

Looking for more examples, I saw some more sentences with this "sometimes this, sometimes that" pattern. I basically understand how to construct a sentence with this pattern, but I also found some where I couldn't' tell what もあれば was doing:

京都から高野山までは、3時間もあれば行ける距離です。
Kyoto is about 3 hours distance from Mt. Koya

10分もあれば支度できます。
It only takes me 10 minutes to get ready

What is もあれば's function in the last two examples?

Answer

ば is conditional just as in the first example. も in these cases means something like 'as less as'. The literal translations are respectively (Don't expect that they are grammatical or natural in English):

(The distance) from Kyoto to Koyasan is such that, if you have as less as three hours, you can get there.

If I have as less as ten minutes, I can get ready.

By the way, although I know that it is not only the responsibility of the English speaking people, I feel it unnatural when people write something like Mt. Koyasan. It is as strange as saying Mt. Mont Blanc, salsa sauce, Volkswagen car, etc.