The Periodic Table

Loong

01:11

!!img/N,N-dipropylcyclohexanamine

Chemobot

Jan

It’s celebrating \o/

Loong

@Jan Now, I really would like to see that answer sheet.

Jan

How come?

Loong

We see so many textbooks and websites with obsolete or blatantly wrong nomenclature; hence, I would like to know whether this test has the correct answers.

Jan

01:44

Let’s see how many upvotes I’m going to get for my just-posted coordination-chemistry answer.

Also, let’s go to bed. Why didn’t I do that an hour ago?

Loong

@Jan Most people die in bed.

user228700

Is anybody here familiar with Le Chateliers's principle?

Loong

@Kaumudi hm?

user228700

I have a quick question. For a solid <--> liquid equilibrium, what will happen if I increase the pressure?

Loong

@Kaumudi Which solid? Which liquid?

user228700

01:55

@Loong Not water.

Loong

OK, so do you assume that the density of the solid is larger than the density of the liquid?

user228700

Yes.

user228700

This means that the volume of the solid is smaller than the volume of the liquid, correct?

Loong

For a given mass, yes.

user228700

The way that I've been taught to think about this problem is like so: Since the pressure has been increased, the equilibrium will attempt to shift in a direction that will counteract this change in pressure. In this case, this would be achieved by shifting in that direction in which the volume is greater.

user228700

01:59

Is this the correct way to think about it?

Loong

If you press on a balloon, does this make the balloon larger?

user228700

No .__. This is exactly the problem. I'm confused as to how this principle actually applies.

user228700

If the following equilibrium exists inside the balloon:

user228700

$$2 A <---> A_2$$

user228700

Upon increasing the pressure, the equilibrium will shift in the forward direction, correct?

Loong

02:03

yes

user228700

OK. Can you please help me to find the flaw in my reasoning whilst proposing the first statement that u sort of disagreed with? What is the correct way to think about this?

user228700

(I find that I'm able to arrive at the correct answer when dealing w/ chemical equilibria. It's the physical ones that give me all the trouble)

Loong

@Kaumudi I guess, you are thinking about something like the ideal gas law when talking about pressure.

p V = n R T

user228700

Yes, I am...

Loong

Such a system cannot use a chemical reaction or a phase change to escape from your pressure.

user228700

02:09

Ah, I see. And why is that..?

Loong

By definition, the ideal gas does not undergo reactions or phase changes.

user228700

Oh, of course. Right.

user228700

In which cases then, should I look to apply the principle?

Loong

So if you change the external pressure at constant temperature, the volume of an ideal gas will simply adjust until the external and internal pressure are equalized.

However, if your gas could condense into a liquid, you get a new way to escape from the increasing pressure.

The ideal gas low cannot describe such a phase change.

Typically, the liquid has a much higher density than the gas.

user228700

OK, I understand. Again, in which cases then, should I look to apply the principle?

Loong

02:16

@Kaumudi The Le Chatelier's principle? You can apply it if you can express you system as an equilibrium A <=> B.

e.g. gas <=> liquid

or liquid <=> solid

or chemically: 2 A <=> A2

user228700

Yes. Alright. What about the liquid <--> solid equilibrium that I brought up in the beginning? How can I apply this principle? i.e. What happens when we increase the pressure?

Loong

If you fill your balloon with the liquid or with the solid, which one presses stronger against the balloon?

(same mass of liquid and solid)

user228700

Uhh. It's difficult for me to imagine this. I really dunno. If I'd have to guess, I'd say liquid.

Loong

Which phase wants to have a larger volume?

user228700

The liquid..?

Loong

02:22

Yes, the liquid phase wants to have a larger volume.

user228700

If given some more energy, the liquid can evaporate and change completely into gas-and the gas phase has the largest volume. That's how I guessed it. Is my reasoning terrible?

Loong

That's ok for most substances. But it doesn't work for some solids such as ice.

user228700

Gosh, it probably is, isn't it?

user228700

OK, given that liquid exerts more pressure than the solid, the equilibrium shifts in the direction of the...solid? (Upon increasing pressure)

user228700

This doesn't make sense to me because the solid has the lower volume, right? And lower volume corresponds to higher pressure. Dang it, I'm probably confusing this with the ideal gas situation again, aren't I? :-/

Melanie Shebel

02:28

Ello

user228700

Hi :-)

Loong

@Kaumudi Ok. So when you increase the external pressure, the system will reduce its volume until the external and internal pressure are equalized. A simple ideal gas will do this according the ideal gas law. Your solid–liquid system can do this by transforming some liquid to solid.

@MelanieShebel Hi. How was you exam?

user228700

The question is, why does some liquid transform into some solid?

Melanie Shebel

It went really well. I didn't get 100%, but I think I did REALLY well.

Loong

@MelanieShebel sounds good :-)

user228700

02:34

Erm..?

Loong

@Kaumudi When you increase the external pressure on an ideal gas, why does the volume of the gas decrease?

user228700

Because it's being compressed...

Loong

Yes, and the same principle applies to your liquid.

user228700

But what about this:

user228700

> "This doesn't make sense to me because the solid has the lower volume, right? And lower volume corresponds to higher pressure. Dang it, I'm probably confusing this with the ideal gas situation again, aren't I? :-/"

Loong

02:39

Yes, again you are describing an ideal gas without phase change or chemical reaction.

You had no problem with a chemical equilibrium:

37 mins ago, by Kaumudi

$$2 A <---> A_2$$

Which side corresponds to a higher volume?

user228700

OK. Can u please direct me to a source to study this principle properly? I haven't found a good one in all the time I've been searching (and searching).

user228700

@Loong Left.

Loong

@Kaumudi OK. And which side corresponds to a higher system pressure?

user228700

Left..?

Loong

Yes!

user228700

02:42

That's strange .__.

user228700

Wow.

Loong

@Kaumudi That's not strange, that's a chemical equilibrium, and not just a simple ideal gas.

user228700

Alright, thank you :-) Can u suggest a good source?

Loong

No sorry, I don't know a good source right now.

But maybe, we can find something tomorrow with better examples.

@Kaumudi So, and if the principle works for a chemical equilibrium like "2 A <---> A_2", you could do the same for "solid <---> liquid".

CowperKettle

Good morning!

I'm trying to select 05 in 31.05.2011 but this regexp fails for some reason

It works only if I remove the ^ and the $ at the left and right ends

pentavalentcarbon

02:59

That's gross. Let me try it on regexer.com

CowperKettle

Why is it gross? This is the second time ever I'm using regexp, so it might be a bit unwieldy

Melanie Shebel

Regex gets gross easily. For everyone, seasoned or not (so don't feel bad.)

pentavalentcarbon

Maybe it's the kind of work I do but in my 5 years of programming seriously I've never needed lookarounds.

Groups, sure. Lookahead and lookbehind, no.

CowperKettle

I read a little about "capture group" but understood nearly nothing.

pentavalentcarbon

Ahhhhhhhh. I see.

Capture groups are very handy and I think you need them here, but the stuff with question marks I don't think so. I'll try it.

CowperKettle

03:07

0

Q: Regexp search in SDL Trados (a translation tool)

In the document I'm translating there's a large number of dates of the type 12.05.2011. I need to replace the month numbers (in the middle) with month names, like -May-, which would give 12-May-2011. This is necessary because some readers might assume that the month number is in the beginning and...

regex

pentavalentcarbon

Do you know what the ^ and $ do?

CowperKettle

Yes, they indicate "the start and the end"

meaning, there should be nothing but our string in the whole body of search

pentavalentcarbon

Ok. There might be some invisible characters in the string then that prevent the match.

CowperKettle

No, there are no invisibles, it seems

This regexp managed to "find" the string

If I use a capture group like this - ^[\d]{2}(\.05\.)[\d]{2,4}$ - should it only capture .05. for replacement?

user228700

03:22

@Loong OK. Thank you :-)

pentavalentcarbon

The capture group just gives you a reference to work with for later on.

For example, sed 's|$\d*$\.05\.$\d*$|\1-May-\2|' < test.

I keep the first and third parts of the date for use in my replacement. That's the \1 and the \2.

Now, I don't think you can do that here.

CowperKettle

a guy offered this: (?<=[\d]{2})\.\d{2}\.(?=[\d]{2,4}[\r\t\n\s])

I've no idea what [\r\t\n\s] is

pentavalentcarbon

Those match hidden characters: \r is carriage return, \t is tab, \n is newline, \s is space.

The problem is because they're in [] and not []*, it will only match one of them, not an arbitrary number or a combination of them.

CowperKettle

@pentavalentcarbon but with the asterisk, it will match even zero of them

pentavalentcarbon

Yes.

I guess I have a stupid question.

Why does it matter that you can't get ^ and $ to work?

CowperKettle

03:30

Thank you, but I want to search for strings that fill the whole translation segment, because there might by chance be some non-date string, say, some production code, 2135.05.2011.462, and my search-and-replace might wrongly put -May- in there. ^_^ That will wreck my translation. — CopperKettle 12 mins ago

pentavalentcarbon

Ok, that answers my question.

In that case, you will still need to make an assumption as to what your date string will look like.

For example, will it always be dd.mm.yyyy?

Oh, I see that's why the {} are there.

CowperKettle

(0:

@pentavalentcarbon excuse me for stupidity, but what is sed 's?

pentavalentcarbon

Sorry. That's the Unix command line tool sed, followed by a command that replaces text based on the regex.

CowperKettle

ah! thank you!

pentavalentcarbon

The one I wrote doesn't do what you want though, you can ignore it.

Melanie Shebel

03:42

Man, a lot of turds on the front page tonight.

CowperKettle

in the news, or on Chem.SE?

Melanie Shebel

Chem.Se

Well... both.

CowperKettle

heh

Frank Zappa - Trouble Every Day

►

pentavalentcarbon

Frank Zappa is telling everyone from his grave "I told you so" right about now.

user228700

Can anybody please tell me why the number of $\alpha$ hydrogen atoms decides the stability of the molecule more than the cis/trans effect?

user228700

03:46

Melanie Shebel

That would be a really good question for the Chem.SE (if you feel up to drawing that out w software.)

user228700

(c) has a smaller number of $\alpha$ hydrogen atoms compared to (b) but (b) is more stable! However, (b) is neither cis nor trans...

Melanie Shebel

@CowperKettle Is that your systemwide rep next to your name or your Chem.SE rep?

The 30.4k

CowperKettle

@MelanieShebel the total - my Chem rep is only about 800

user228700

@MelanieShebel Which software?

Melanie Shebel

03:48

Chem Draw or whatever you have to draw chem structures.

user228700

(I'm using a mobile phone :-|)

user228700

Why is it a good question? (b) appears to be neither cis, nor trans...

Melanie Shebel

So, I'm looking at the StackExchange chat rooms and it looks like this one is...

The 7th most popular chat room in the entire network.

Nice!

user228700

I'll ask the question on the main site. Can u please tell me why it is a good question? @MelanieShebel

Melanie Shebel

Oh, I mean, in terms of current activity.

@Kaumudi It may benefit other users vs just answering questions here in chat.

Plus, you'll get more help there vs here in the chat room.

asking*

user228700

03:55

I understand why asking on the main site will be beneficial to a lot more people. I'm asking why this particular question is a good question.

Melanie Shebel

Because it'll help others.

Who might have a similar question down the road.

user228700

Okay. The question seems a bit homework-tsy tho.

user228700

I'm not particularly confident that it will not be closed.

Melanie Shebel

You don't have to write the question if you don't want.

If you word it right and include the homework tag (AND INCLUDE YOUR THOUGHT PROCESS/WORK) it should not be closed.

user228700

Okay. I think I'll wait. Thanks :-)

Melanie Shebel

04:03

If anyone wants to reword the body of this question, that would be amazing. I'm not good w the jax.

0

Q: Finding Diameter of a Atom

So I am looking to find the atomic size of a molecule. So we are given the dimensions of a sheet which is: 1698.03mm^3 Then we are also given that the sheet has a mass of 3grams, and molar mas of 8g/mole So we can do density by dividing area/mass. So 1698.03/3= 566.001mm/g. Then after that ...

everyday-chemistry

Also maybe better tags?

pentavalentcarbon

4 suggested edits in the queue?!?! Is everyone asleep? Here I go!

Melanie Shebel

It's a quiet night!

But there are some real turds on the front page tonight.

user228700

I've a very quick question. Is the resonance effect more consequential for the stability of a molecule compared to hyperconjugation?

pentavalentcarbon

@MelanieShebel I can't even figure out what this is asking. I will accept your edit but this needs a flag. It's totally unclear. I think they want volume of a molecule, but impossible to tell.

Melanie Shebel

Oh volume? Really?

I'm sorry, I didn't read that! I just did a cursory look at the body and the title to clean it up. Sorry.

user228700

04:13

Anybody?

pentavalentcarbon

Well, that's what it said and it was asking, but I think they're totally confused about what they even want.

CowperKettle

I modified my regexp a little: (?<=[0-3][0-9])\.05\.(?=[\d]{2,4}) -- is there a way to limit the first number by the 01-31 range?

Melanie Shebel

@pentavalentcarbon That's possible. I cleaned it up a bit more. Perhaps they'll come back and clarify. (Hopefully.)

They have low rep and their username is noreturn, so perhaps not.

Bahahaha!

pentavalentcarbon

I just noticed that.

$\tiny\text{some of these I wish I could pour gasoline on and toss a match onto...}$

CowperKettle

I wonder if the number of repetitions in the curly brackets will refer to "20" or just to "0": 20{0,1}

What if I want the number 20 to be present either one or zero times?

20{0,1} seems to match even the number 2

pentavalentcarbon

04:26

(20)?

? is 0 or 1 times

CowperKettle

thank you

How does one define a string that would match only a two-digit number from 01 to 31?

Melanie Shebel

Gotta love those "bomb" questions.

CowperKettle

About how to make bombs?

Melanie Shebel

Yeah, one just popped up.

We should have a "I wanna blow sumpin up" tag.

CowperKettle

We should have a "defuse" button for moderators

With a counter with seconds ticking away to zero

Melanie Shebel

04:34

Or a "I'm not being vague on purpose... this is totally legal..." tag

I'm talking about you, alkaloid question!

0

Q: General Alkaloid Extraction Process

I'm getting into alkaloid extraction from various ethnobotanicals. It is a bit frustrating trying to extract alkaloids from ethnobotanicals without good guides out there, and I wanted to make my own techniques and experiments. However, I need to know what the basic outline is for extraction. Are ...

organic-chemistry extraction drugs medicinal-chemistry

pentavalentcarbon

I hate that crap and I wish it would just go away

Melanie Shebel

Yeah, well see the latest post on meta!

ahem

CowperKettle

Klaus is a great guy. I remember he gave a great answer to me

It looks like in Trados, you should put the ^ and the $ inside the lookbefore and lookbehind brackets, like this: (?<=^[0-3][0-9])\.05\.(?=[\d]{2,4}$)

I'm not sure, but it seems to work

pentavalentcarbon

I'm not sure if this is the best way, but the first thing that came to mind was 0[1-9]|[1-2][0-9]|3[0-1].

CowperKettle

@pentavalentcarbon thank you!

Melanie Shebel

04:40

867-5309

pentavalentcarbon

ugggghhhhhhh

I don't know enough about regexes or lookarounds to understand why it works when you put those inside.

CowperKettle

don't think twice, it's allright

Melanie Shebel

Klaus didn't ask it, he edited. We had a fun discussion about the question here the other day. :D

Klaus answers like all my questions, he's fab.

Martin - マーチン

05:34

@hBy2Py That is a really good question. Unfortunately I have to go through some hoops to get Pople's original paper, and I'm a bit too lazy to look up the input specifications for qchem. But that's not really the main focus of the question. If you find the exponents, you'll somehow find the way to give them to the program.

@hBy2Py Thanks a lot for the input. I have just downloaded it now. Unfortunately I realised that I don't have the time to look into it right now O.o (I forgot about a meeting I need to prepare for.) I hope I get around to it during hat season. Did I read correctly, that you are not using a queuing system, but only run it interactively?

I also just read they are coming out with version 4.0 soon. (I really hope they implemented the reparametrised DFT functionals by Grimme.)

2

1,3-feeds

06:01

1

Q: Homework requests in Periodic Table chat?

I don't mind guiding users in The Periodic Table with their homework. If I get a question or two, I'll discuss with the person. However, there have been times where users will sit in chat all night and ask question after question, seemingly completing entire assignments in chat. There have been c...

discussion chat

Martin - マーチン