The Periodic Table

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12:17 AM

Q: When 2-pentene reacts with HBr, what will be the major product?

If we consider the first step (formation of carbocation by the attack of the proton). A couple of textbooks I referred say that when the substituents on the $\ce{C=C}$ are different, the direction of shift of the electron is decided by the inductive effect of the substituents. For example, in th...

orthocresol

12:37 AM

@Mithoron I saw your "citation needed" flag not from the flag queue, but by manually searching for that question. Then I realised you were already ahead of me in the search for a duplicate...

And now the question you linked has an answer which claims that the hypervalent resonance structure is the most important...

9 hours later…

Martin - マーチン

9:12 AM

@Loong You probably have one of the best knowledge on this: Does the p in the equilibrium constant K_p have to be upright or italic? I think it should be italic, hence I corrected it in the post and left a comment saying that it is completely wrong to mhchem. He responded as below:

@Martin-マーチン Why would you say that? p, in that case is not a variable, i.e. it does not stand for a number, but it stands for "in terms of partial pressures". In my humble opinion, the subscripts of Kc ("in terms of molar concentrations") and Kp should be upright. This is different from $C_p$ ("at constant pressure") where $p$ could stand for any pressure ($C_\pu{100 kPa} = C_\pu{200 kPa} = \ldots$). (Should we move that discussion to somewhere else?) — mhchem 1 hour ago

Loong

Don't we explain that somewhere on meta?

I will check.

IUPAC says:

> Subscripts and superscripts that are themselves symbols for physical quantities or for numbers should be printed in italic type; other subscripts and superscripts should be printed in Roman (upright) type.

So, if that p is a symbol for the quantity "pressure", it should be italic.

ISO says about the same:

> A subscript that represents a physical quantity or a mathematical variable, such as a running number, is printed in italic (sloping) type.

Loong

9:45 AM

Similar also in the SI brochure, although not so clear for this case. They use the C_p example, too. And make a reference to the ISO standard.

Anyway, back to the IUPAC Green Book:

> equilibrium constant, pressure basis $K_p$

i.e. both symbols italic

Likewise for

> equilibrium constant, concentration basis $K_c$

The same in ISO 80000-9:

> equilibrium constant on a pressure basis $K_p$

> equilibrium constant on a concentration basis $K_c$

M.A.R. ಠ_ಠ

P.S. K_p looks cool.

QED.

Wait, both italic?

Now that's uncool

Loong

By the way, M.A.R. should not be italic. So we should remove your RO status.

M.A.R. ಠ_ಠ

(╯°□°）╯︵ ┻━┻

Units should have a space beforehand. Loon g

2 hours later…

Bounty Hunter

11:31 AM

Q: How dependent are computed charges using the quantum theory of atoms in molecules on the used level of theory?

The quantum theory of atoms in molecules is based on the topology of the electron density. This mathematical analysis allows to find critical points and hence has a unambiguous way of separating a molecule into atoms. Each atom can be assigned a basin, and integrating the electron density in it y...

quantum-chemistry computational-chemistry

Loong

12:13 PM

@Martin-マーチン I made an edit to the meta post.

1 hour later…

mhchem

1:29 PM

@Loong Well, the IUPAC Green Book writes $K_m$ ("molarity basis") while in the UIPAC's "On the use of italic and roman fonts for symbols in scientific text", they insist that $C_{p,\mathrm{m}}$ has an upright m for "molar".

So, they are inconsistent.

@Loong I still don't see how the p in Kp "represents a physical quantity". (Wikipedia: A physical quantity is a property of a material that can be quantified by measurement. A physical quantity can be expressed as the combination of unit by a number.) Yes, pressure can a physical quantity, but in this case, the p is a shortcut for "expressed in terms of partial pressures of gases". You cannot give that p a number+unit (or multiple numbers+unit). Same for Kc.

Loong

1:46 PM

@mhchem No, that's not inconsistent. "molar" and a "equilibrium constant based on molarity basis" are not the same thing.

Although $C_{p,\mathrm{m}}$ actually is not correct. It should be $C_{\mathrm{m},p}$

M.A.R. ಠ_ಠ

mathrm all teh things

Hey, Cabbage, you're back

I forgot where you were gone in the first place.

Loong

@M.A.R.ಠ_ಠ The next part "2 molecules of Hydrogen and 1 molecule of water should give 3 molecules of water vapor" isn't much clearer.

M.A.R. ಠ_ಠ

@Loong That part, I think, they mean "if this law were true, 2H2 + O2 -> 3H2O"

There should be a dupe for that somewhere

Loong

Yes, there are a few similar questions.

Q: is avogadro's law for the same gas?

Avogadro's law is V1/n1 = v2/n2 - volume and number of moles are directly proportional. My question is - can this law apply to two different gases - for example, Hydrogen with volume v1 and number n1, and Oxygen with volume v2 and number n2 - are they proportional?

physical-chemistry stoichiometry gas-laws kinetic-theory-of-gases

Q: Avogadro's gas Law doesn't make sense? (it does actually)

It says equal volumes of all gasses under same conditions of temp. and pressure contains the same number of atoms/molecules. Now suppose you have 1L of Chlorine in a box and 1L Hydrogen in another box , now the comparitively huge size of the Cl atom means less of it will fit in the box , whereas...

gas-laws

M.A.R. ಠ_ಠ

2:02 PM

Some of these misunderstandings remind me of when I'm stuck in soduku.

Mental lock

Q: Are all fatty acids monocarboxylic acids?

This answer for this question might solve a multiple choice in my previous chemistry exam.(which caused an argument with my teacher) We know that fatty acids form fats and oil due to their carboxylic groups by forming triesters with glycerol. But is it possible to have a fatty acid with two or ...

organic-chemistry carbonyl-compounds fats

Pretty sure this is fat shaming.

Or maybe fat naming?

2 hours later…

1,3-feeds

3:40 PM

Q: Renaming the homework policy

There seems to be some interest in going over the infamous homework policy. Imho reviewing all of it in one go and coming up with something new is simply not feasible. We should go about attacking it in small pieces. Firstly change its name homework policy is a very very very very bad descri...

discussion homework

M.A.R. ಠ_ಠ

No. NO. NOOO!

. . .

Shrug I felt too lazy to write the next discussion anyway

2 hours later…

Bounty Hunter

5:17 PM

Q: Molecular orbitals of the enolate ion

The reactivity of the enolate ion is most frequent explained with reference to its system of $\pi$ molecular orbitals. The image below taken from Wikimedia Commons depicts this system of $\pi$ molecular orbitals. $\ce {C}$-alkylation is favoured when the orbital interaction with the $\ce {HOMO}$ ...

organic-chemistry molecular-orbital-theory

mhchem

5:48 PM

@Loong And which of the two is a physical quantity, a number or a mathematical variable?

Neither "molar" nor "based on molarity basis" are.

Loong

5:59 PM

Molarity is a quantity, even though the use of this name is deprecated.

1 hour later…

mhchem

7:08 PM

Well, allow me to I see a conceptual difference between "molarity" itself and "based on molarity". Could you replace the letter with number+unit (or a set thereor), is my rule of thumb.

On the other hand, I don't see a difference between "molar" and "based on molarity". Isn't a "molar enthalpy" the "enthalpy based on molarity"?

But, in the end, it is all just a convention. I'd like to hear ICTNS's opinion on this.

3 hours later…

Michael Lautman

9:50 PM

This late answer came up on the review list.
What is the policy/culture on dealing with snarky answers like this.
The answer is by a new user and is neither helpful nor courteous... suggestions?https://chemistry.stackexchange.com/questions/5811/unit-of-the-equilibrium-constant-contradiction-of-bridgmans-theorem/116410#116410

orthocresol

10:27 PM

@MichaelLautman I don't think you can do much better than what you did there. If you find it terribly unkind, then you can flag as rude/abusive, but that should generally be reserved for severe cases. Otherwise, downvote and move on ;)

@mhchem not really though, molar enthalpy isn't related to concentration (molarity)

Michael Lautman

@orthocresol thanks...

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