The Periodic Table - 2016-09-24

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getafix

01:53

-1

Q: Describe energy (of a system) properties in a substance and give some examples?

It was my physical chemistry homework. I was tasked to answer it in qualitative perspective. I really can't understand what the question really means.. Am I supposed to: explain one form of energy, like heat, and the application of heat in a system? Say that the system is a tea in a glass, an...

homework physical-chemistry energy heat

What's this supposed to mean? I don't get this post..

user228700

02:11

@Loong: Hello :-) Since I received an answer for my question even before new answers were posted, I'm wondering if I should accept an answer or not, since that would mean that you'd lose 50 points. I should also mention that none of the answers are as satisfactory as the answer I first received so that's the other reason that I'm hesitant to accept any of the answers posted.

getafix

02:32

@KaumudiHarikumar I think this is between you and Loong, but I think the purpose of a bounty is draw more attention to an question by promising a reward, in this case 50 rep. People posted answer in the hopes of earning said reward, and removing it now would be unfair to them

user228700

02:53

@getafix OK. I'll wait for @Loong to respond though.

user228700

Also, just one person has posted an answer so far. I'm gonna wait for at least 3-4 days before I go ahead and hastily accept an answer.

getafix

last I saw there were two?

orthocresol

03:08

1. Bounties are non-refundable. 2. Bounties are non-cancellable. stackoverflow.com/help/bounty

I swear I dreamt of that stupid heat capacity question last night

getafix

03:19

Hahaha, still haven't found it?

Btw, @orthocresol great job on O-O and S-S bond question..!! It was a delight..

@orthocresol I did try looking for the heat capacity question, you did offer a big bounty ;) no luck though

orthocresol

03:31

@getafix You know, if two hours of my best searching efforts couldn't find it, I think it might just be worthwhile to write a new question...

UGH

getafix

03:48

Umm perhaps

What was it about though? Like precisely..do you remember?

orthocresol

04:02

It was just about Cp - Cv = nR

although it could be in many guises for example Cp,m - Cv,m = R

i believe there were at least two answers, one of which simply stated that for an ideal gas, U = 3/2 nRT

But I don't like that, because that's only half a proof, that is not the definition of an ideal gas and you don't need it to prove the equation anyway

So I wanted to write a more rigorous proof, but now I can't find the question.

You can see my chem.SE to-do list on my profile information, actually.

orthocresol

04:21

Maybe it was the perfect gas/ideal gas question and I just remember wrongly.

sobs

I looked through all the results for "[physical-chemistry] answers:2" and couldn't find it.

user228700

04:40

@orthocresol Oh, shucks :/

user228700

I've got a quick question. Textbooks keep referring to "Enthalpy" as the "heat content of a system". In my understanding, the quantity heat is only defined during processes and it is not a state function. On the one hand, people say " It is meaningless to talk about the heat content of a system" and on the other, people are defining enthalpy as the heat content of a system! What is the more useful definition of enthalpy that u have found..?

getafix

05:06

@orthocresol is it possible that it was flagged/deleted?

I would like to write a proof along those lines too actually haha

orthocresol

@KaumudiHarikumar H = U + pV.

That is the definition of enthalpy

If you say it is the heat content of the system, that is an interpretation, not a definition

@getafix It is possible that I just remember wrongly. :(

@KaumudiHarikumar Also, you are right, heat is only defined for a process, not a state.

However, enthalpy changes are equal to heat changes, for a process at constant pressure.

Most chemical processes are constant pressure (think of doing a reaction in a test tube - everything is at atmospheric pressure), which is why some books may equate heat and enthalpy.

user228700

@orthocresol You mean constant volume..?

orthocresol

No, I mean constant pressure.

At constant volume, heat change = internal energy change

"heat change" is not really correct terminology, but I will let it slip...

user228700

@orthocresol Yes, OK.

orthocresol

Nah, it is my bad phrasing, not yours. What i called heat change should be more properly called "heat supplied to the system"

user228700

05:15

I was wondering why we use this term(enthalpy)instead of plain old internal energy when speaking about bonds. Bonds are created so that's why we include the expansion work too?

orthocresol

Simple, because $q = \Delta H$ for const-p whereas $q = \Delta U$ for const-V

and const-p is more applicable than const-V

for most chemical applications

If you were to define a chemical process at const-V, then you would use internal energy

However, most of us define chemical processes at const-P, hence enthalpy is our friend.

CowperKettle

\o

orthocresol

@CowperKettle hi

CowperKettle

Is "molecular weight" used more often than "molecular mass"?

orthocresol

@CowperKettle Although it is not strictly correct, yes, MW is much more common.

CowperKettle

05:18

@orthocresol Thank you! Because in Russian the standard phrase is "molecular mass".

orthocresol

@CowperKettle See, Russians know science better than we do.

shakes head at IUPAC

CowperKettle

My TRADOS dictionary suggests "molecular weight" all the time, and I follow its suggestion

user228700

@orthocresol OK. Thank you very much :-)

orthocresol

@KaumudiHarikumar No problem.

getafix

05:33

Yeah in general, people confuse mass and weight in common usage all too often and it annoys the shit out of me

orthocresol

@getafix see, I'm primarily an organic chemist, (or I will be after I finish struggling through this year of inorganic and physical), so I don't really care that much :D

CowperKettle

> In order to determine the molecular weight of the non-glycosylated protein, we used PNGase F to separate N-glycans from the protein molecule.

I wonder if there's a better verb than 'separate'

orthocresol

05:49

I don't know the context well enough to judge.

I think it is trying to cleave the groups?

or remove the groups?

CowperKettle

cleave might be better, thank you

orthocresol

Separate suggests that they are not covalently bound whereas I think this case it is trying to remove a covalently bound group.

If that's the case I'd go with cleave

CowperKettle

nods

getafix

@orthocresol I see haha. I really don't know what I will be sigh..

orthocresol

@getafix well, I changed my mind several times. For a really long time, I wanted to do medicine

So there's no guarantee that this time next year, I will still want to do organic :p

CowperKettle

05:59

Do biotech, man

Gene modification, etc. (0:

orthocresol

@CowperKettle You actually need to know a lot of bio to do that

It's really cool, and probably most people in the scientific community have heard of crispr-cas9, but I'm not feeling the love for bio right now :(

CowperKettle

Clustered regularly interspaced short palindromic repeats (CRISPR, pronounced crisper) are segments of prokaryotic DNA containing short repetitions of base sequences. Each repetition is followed by short segments of "spacer DNA" from previous exposures to a bacteriophage virus or plasmid. The CRISPR/Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages, and provides a form of acquired immunity. CRISPR associated proteins (Cas) use the CRISPR spacers to recognize and cut these exogenous genetic elements in a...

orthocresol

they're gonna get a nobel prize

getafix

I was into biochem but then my interests moved to supramolecular Chem

Think I'm gonna see how that works out, cause I like all of Chem..haha hard for me to narrow down

CowperKettle

I never even heard of supramolecular chemistry

Supramolecular chemistry

Supramolecular chemistry is the domain of chemistry beyond that of molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components. The forces responsible for the spatial organization may vary from weak (intermolecular forces, electrostatic or hydrogen bonding) to strong (covalent bonding), provided that the degree of electronic coupling between the molecular component remains small with respect to relevant energy parameters of the component. While traditional chemistry focuses on the covalent bond, supramolecular chemistry examines the weaker...

getafix

06:07

So yeah let's me do a bit o organic and inorganic in supramolecular Chem

CowperKettle

Supramolecular looks like a thing done more behind the monitor than with the beaker and tube?

getafix

Well it's broad. I have been spending my summer in a supramolecular lab, and although I have only been doing literature review..the lab has a heavy organic synthesis focus

Anyway might be moving to an organic lab after my summer vacation ends because right now, the lab I am in can only let me work over vacations

Stupid rules in my university..even right now I kinda forced them to make an exception

Rubisco

@Wildcat yay

CowperKettle

> In order to determine the molecular weights of the light and heavy chains, the samples were treated with a reducing agent to cleave the light and the heavy chains apart. (That's better ^_^)

Morning, Muḥammad

Rubisco

06:22

\o, Art

I wonder if 'Arty' is better.

CowperKettle

> In order to determine the molecular weights of the light and heavy chains, the samples were treated with a reducing agent to cleave the light and the heavy chains apart: to an aliquot containing 10 μg of protein we added 15 µl of 10 mM DTT solution in 100 mM bicarbonate buffer.

I don't get this. Would not the mM's go all awry if we mix 10 mM with 100 mM? Whatever.

@Rubisco Choose whatever you like best. Some friends call me Tyoma (hypocoristic)

or Tyomych (hypochoristic familiar)

Rubisco

Terrible sickness.

CowperKettle

(0:

Rubisco

Oh wait. Hypochorism isn't a sickness

CowperKettle

It's not ty-oma in Russian, but a single sound: Tёма

The letter ё stands for a short "yo" sound (the syllable with ё is always under prosodic stress)

We transliterate English first as фёрст

Rubisco

06:30

O.O

Russian is too Greek to me.

CowperKettle

(0:

Enroll in a Russian university, and you will learn it quite fast

getafix

Greek is Russian to me and and Russian is Greek to me

O.o

Rubisco

-2

Q: Magnet - Does northpole attracts electrons?

I'm having hard time understanding how magnet works... I just want to know why magnet is used to generate electric energy (electric generator), does the magnet's northpole attracts electrons and its southpole repels the electrons?

This question made my day

CowperKettle

Could you perhaps rephrase your question? As it stands right now, it is very hard to tell what exactly do you want? — getafix 4 hours ago

> As it stands right now, it is very hard to tell what exactly you want. (Correction. See "Penthouse Principle" on Wikipedia) ^_^

I also often invert subject and verb in subordinate clauses. (0:

Rubisco

I do do do's a lot

getafix

06:35

Hahahah @CowperKettle yeah thanks for pointing that out

Rubisco

Thanks for pointing that out when he can't fix it

CowperKettle

@getafix No problem! (0:

getafix

When I am usually commenting on posts, I'm doing it from my phone and I'm on the move, so I don't pay a lot of attention

Rubisco

Who does

CowperKettle

I commit this error even while typing. (0:

Rubisco

06:37

You're being too distracting. I'm not really enjoying this ice cream

CowperKettle

But @snailplane corrected me once, and now I notice this error in other's writing.

Rubisco

others'

Apostrophe is English's biggest cancer.

CowperKettle

nods

Apostrophes' role in English is not very big, thankfully.

Rubisco

BWAHHHA now you'll correct me whenever I put a wrong apo'strophe somewhere

CowperKettle

(0:

Rubisco

06:43

in English Language & Usage, yesterday, by RegDwigнt

> This theme is more epic than almost anything Han's Zimmer has made.

getafix

Hahaha

i think orthocresol found the question he was looking for

Rubisco

Yay for him

orthocresol

I didn't find it, I made it

getafix

Yeah lol just realisd

Rubisco

You're alive

orthocresol

06:52

Of course, I was taken by the Germans to the rescue centre

Rubisco

That was a graveyard in disguise

PSA

Ortho's now a zombie.

getafix

soon

I might write an answer to that too..

very soon

should I use $dU$ or $\mathrm{dU}$?

Rubisco

d is upright, U is slanted.

So none of them.

orthocresol

\mathrm{d}U

getafix

ah okay thanks

user34388

07:30

Does 3c2e bond exist in any cyclopropane-derived radicles/ions?

!!img/C3H5+

Chemobot

user image

user34388

ah

!!img/C1[C+]C1

Chemobot

No result found.

user34388

wait, would the cyclopropanyl cation be in resonance with the allyl cation?

getafix

08:07

how do i display a strikethrough in tex?

i tried \cancel{} doesn't work

1 hour later…

getafix

09:31

1

Q: Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR

For an ideal gas, we have $$C_p - C_V = nR$$ How can I prove this?

physical-chemistry thermodynamics gas-laws

Wrote an answer to 0-cresols question.

Rubisco

-10

Q: I am informed. What does that mean?

I am informed. I just wanted to participate Stack Exchange. But I can't get it. What does that mean? And, how does Stack Exchange control me on being informed?

support badges informed-badge

getafix

09:42

LOL

orthocresol

10:25

-1

Q: do soluble halides form colorless solutions?

do soluble (H.A.L.I.D.E.S.) form colorless solutions? do soluble (H.A.L.I.D.E.S.) form colorless solutions? do soluble (H.A.L.I.D.E.S.) form colorless solutions? do soluble (H.A.L.I.D.E.S.) form colorless solutions? **do soluble (H.A.L.I.D.E.S.) form colorless solutions? **

solutions halides

Wildcat

10:39

=^.^=

Bounty Hunter

1

Q: Where is bifurcation situated on cyclohexane isomerisation PES?

I am wondering what does PES for cyclohexane isomerisation looks like. I have two possibilities in mind but each has some kind of vagueness. 1) Starting from boat conformation minimum, followed by transition state, then bifurcation, after that two separate paths leading to halfchair transition...

organic-chemistry quantum-chemistry computational-chemistry isomers books

Loong

11:42

@KaumudiHarikumar Don’t worry! You should accept the answer that solved your problem and that was most useful to you. However, you don’t have to accept an answer now; you may wait, which is also a small invitation for more answers.

The bounty is mainly paid to attract attention to the question. Nevertheless, I can award the bounty to any answer, regardless of the answer that was accepted by you.

user228700

@Loong Oh, I didn't know that it's possible to do this! OK, I'm gonna wait to see if it receives any more attention. Thank you :-)

Shadock

11:55

Hello ! :)

Loong

12:33

@KaumudiHarikumar chemistry.stackexchange.com/help/bounty

@Shadock hi

getafix

12:54

@Shadock hey

1 hour later…

Rubisco

14:24

Thanks Ortho, you earned me a badge.

Wildcat

@Rubisco: Aloha! New username yet again?!

And new avatar.

Rubisco

@Wildcat You seem to have gained foretelling powers

Wildcat

:D

getafix

3

Q: why do the polysaccharides consisting of alpha-glucose have helical structure?

why do the polysaccharides consisting of alpha-glucose such as starch and glycogen have helical structure,while the one such as cellulose consisting of beta glucose doesn't have ? The textbook said that is because of the angle of 1-4 linkage,what kind of the angle is it that makes helical structu...

organic-chemistry biochemistry

Would someone care to weigh in on this? i posted an answer, but I am not sure about i t

also, @Wildcat o/ hullo!

Wildcat

@getafix: hi!

CowperKettle

14:35

> why do the polysaccharides consisting of alpha-glucose have helical structure? (unnecessary"the")

(0:

getafix

How goes?

CowperKettle

okay

\o

Wildcat

English articles...

getafix

haha

orthocresol

@Rubisco What badge was it? :D

Rubisco

14:40

@orthocresol Popular kid

I mean question

orthocresol

@Rubisco Thank @Jan ;)

Rubisco

For hating inline fractions?

orthocresol

For bountying it

Loong says no inline fractions

However, where it is necessary to include fractions in the body text, they shall, where possible, be reduced to a single level by using a solidus (/) or, where applicable, the negative index.

Rubisco

Yessir mister president

getafix

solidus..reminds me of phase diagrams yuck

Rubisco

14:47

@Ortho I just unaccepted so it may get a couple of other answers.

You still would get your bounty I reckon?

I'd raccept after the bounty ends.

getafix

That answer would be hard to beat.. haha

orthocresol

No problem, it's your question after all

Loong

user image

2

Rubisco

@Loong Huh, it says it's not found but I found it after clicking on it

getafix

hahaha

Loong

14:58

Actually, the last three years are more like "I'm done with writing my thesis." – "Well there's one thing more, but then I'll be done."

getafix

Well it'll be awhile before I experience that haha

orthocresol

@Loong "I just need to get a nice a mass spec for this compound. Shucks, I have no more of the compound. Shucks, I need to synthesise more of it. Shucks, I need to order the starting material."

... thesis completion date pushed back by two weeks

Wildcat

15:27

@Loong +100500 XD

4 hours later…

Rubisco

19:06

0

A: Why is a S-S bond stronger than an O-O bond?

Sulphur atoms are larger than oxygen atoms. Pi bonds are formed by overlapping of two parallel p orbitals.Further the distance between atoms,lesser the overlapping and weaker the bond. But sigma bonds in case of Oxygen and Nitrogen are not strong enough because you are bringing two very small ...

Well . . .

Rubisco

19:25

2

Q: Allow mods or gold tag badge holders to prevent question from being on hot network questions list

Sometimes a question that is not representative of a site makes the HNQ list. This can lead to a large bump in traffic on a question a community may not be well equipped to handle. I propose that mods and gold badge holders in the tag be able to set the "hotness points" to zero (or vote to reduce...

feature-request hot-questions

Good idea, this is.

Rubisco

19:44

Wow a meta-answer actually serves as a sort-of answer on Main SE. — user21820 5 hours ago

Huh

Jan

20:29

@Rubisco Wait … wot's main.SE?

Wildcat

Hi @Jan!

1 hour later…

Jan

21:40

Hi @Wild

Mithoron

@Jan o/

chemistry.stackexchange.com/questions/59657/…

Deleting my comments with their question :( Typical

Jan

22:13

Didn't even wait for the third downvote =O

Mithoron

Maybe I was too hmm too critical, strict or sth... Could this question be undeleted?

After some editing it might be not bad, add some explanation for noobs and could be useful

Jan

@Mithoron I dropped an undelete vote for you. But it would need two other trusted users to trust you, too. Mind you, in its present from the question is … somewhere between debatable and misunderstanding concepts, so you may just want to try a different strategy.

(Ron, Klaus, Ben, Dave and the mods qualify)

(God damn, deleting and undeleting without mods is hard xD

Wanna ask on meta?

Mithoron

Ah, I still wanted to make it dupe so meh.

But I thought about meta question about revolving/not revolving electrons. Or making a question on main that would clear it.

Jan

And I bothered for you D=

As always, feel free to ask and self-answer one ;)

Mithoron

:D Well before OP deleted. Now I got more serious thoughts :D

And I got another three suggestions deleted, it seems.

Getting rep from suggestions isn't so satisfying it seems

Jan

22:30

How are suggestions deleted?

Mithoron

Well I lost 2 and later 4 rep - not a big deal but it's like retgone

Jan

(I totally didn't misread that, no.)

Mithoron

I guess if question or answer is deleted after I edited then rep from suggested edit is gone

Jan

1

A: Lost reputation from suggested edit approval on post left behind when account is deleted

In order to give a user reputation for a suggested edit being approved, a "vote" has to be created. The VoteTypeId is 16 and labeled "ApproveEditSuggestion" - and it gets created with a reputation increase of 2 and assigned to the last user who voted to approved the suggested edit. In cases where...

Mithoron

Nah, I don't see user removed. Just nothing

So it's rather removal of post not user

Jan

22:41

Nothing is indeed very weird. You didn't downvote anything, did you?

Oh … maybe that too gets reversed if the post's absolute score is less than 3.

Mithoron

Such things are in rep history.

Whatever, bye

Jan

gnite o/

Mithoron

16

Q: Do you lose your +2 edit rep if the edited post is subsequently deleted?

Do you lose the +2 edit rep if the edited post is subsequently deleted? It seems a little unfair if this is true, but reputation can evaporate in this way in similar circumstances.

support deleted-questions deleted-answers suggested-edits sandbox

And bye again :D

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Transcript for

Sep '1624

The Periodic Table

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