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Mew
1:00 PM
but currently only admins can edit another's post i guess
 
@Mew Probably good idea
 
Mew
@koolman never, it will evolve
2
 
How
 
Mew
@koolman gradual developments over time forever
 
1:04 PM
@Mew great
 
1:20 PM
What do they mean by disorder of molecules
@JohnRennie
Why for reversible process it reamins constant
Sorry , but I got the answer of first question.
@JohnRennie
 
rob
@koolman Wouldn't you consider atoms on a crystal lattice to be "more orderly" than those same atoms zipping about in a gas?
 
Yeah @rob
 
rob
@koolman So then the gas is "more disorderly" than the crystal, and the liquid is somewhere in the middle.
 
Then solid
 
rob
It's a sloppy mapping of the mathematical concept of entropy into the messiness of language.
@koolman "crystal" == "solid"
 
Mew
1:33 PM
@koolman, you can choose any specific configuration you like to be the "ordered" configuration however over time the system will move away from this configuration and thus become "disordered"
 
@rob but if disorder is more than how entropy is more
 
Mew
entropy is a measure of disorder
 
rob
@koolman "entropy" ≈ "disorder"
 
Ohk
Does it depend on velocity of particle
 
Mew
well the faster the particles, the more quickly they will move away from their "ordered" state
 
1:36 PM
Hence they have more entropy
 
Mew
yes
we usually look at Temperature rather than velocity
 
rob
@koolman A fast particle has more "phase space" of possible velocity vectors that it can live in than a slow particle. More indistinguishable possibilities == more entropy
 
More the temp. More the entropy
Am i correct
 
rob
@koolman Usually, but that's not ironclad.
 
@rob i see
 
Mew
1:37 PM
The higher the temperature, the higher the kinetic energy of each particle
well the higher the average kinetic energy
0.5mv^2 = kT where k is a constant and T is temperature
 
rob
Temperature tells you about the relationship between internal energy and entropy
 
@rob ironclad ??
 
Mew
yes my formula only applies to ideal gasses
 
@Mew yeah
 
rob
@koolman "ironclad" == "iron-clad" == "dressed in armor" == "unassailable and always true"
 
1:39 PM
@rob both are dependent on temperature
@rob okay
 
rob
@koolman In statistical mechanics you get a definition of temperature as (1/T) = –(∂S/∂U)
 
And why for reversible process entropy remains constant
@rob i see
 
Mew
Well a law of physics is that entropy never decreases
 
Why
 
Mew
So if a process increases entropy, it must decrease entropy in reverse (but this is impossible because entropy never decreases)
 
1:41 PM
If there is decrease in temp. Then
 
rob
@koolman If your system can evolve either to a lower-entropy state or to a higher-entropy state, the higher-entropy state is overwhelmingly more likely
 
Mew
therefore reversable processes must have 0 change in entropy
 
rob
So much more likely that the possibility of evolving towards a lower-entropy state is negligible for anything that's macroscopic
If you observe a process that goes back and forth reversibly, the two states must have the same entropy
 
@rob i could not able to understand this
Can you explain me in different way
 
rob
@koolman I'm contaminated by statistical mechanics :-)
 
Mew
1:43 PM
@koolman suppose i have a mixture of two different colourd liquids, blue and red
 
Ok
 
Mew
The high entropy state is when the colours are completely mixed
 
Yeah
 
Mew
the low entropy state is when all the blue liquid is on one side of the glass, and all of the red is on the other side of the glass
 
Yes
 
Mew
1:44 PM
What is the probability that all the molecules move from the mixed state to the unmixed state?
virtually 0.00000000000000000000000......1
and thee more molecules i have, the less likely it will happen
 
Yes
 
Mew
now the universe is gigantic with so many molecules it's virtually impossible for these disordered states to move toward ordered states
the universe always tends to become more "mixed" and disordered
 
Oh i see
 
rob
@koolman You can also think about it with countable systems, like playing cards.
 
Yeah
 
rob
1:46 PM
When you buy a new pack of playing cards and open it, usually the cards are sorted: first spades, ace, two, three, ... king, then each of the other suits.
 
Mew
what is the chance you keep shuffling and get a deck in perfect order?
 
rob
If you use the cards for anything then they get put back in a different order.
 
Mew
now imagine the deck has billions of cards in it
it's even more unlikely they will ever get ordered again
 
Ohh i see
 
Mew
This is a nice way of thinking about this as a beginner
When you learn stat mech you'll learn all the maths behind these analogies
but ultimately it's all statistics
 
1:47 PM
Yeah
This examples cleared my doubt
@rob @Mew thanks a lot
But why for irreversible it is not zero
 
Mew
because if entropy was 0 then it is reversible
 
rob
@koolman the change in entropy determines whether a reaction can proceed in one direction, the other direction, or both directions
depending on whether the change is positive, negative, or zero.
 
@rob hence in reversible process the reaction will not proceed in any direction
@Mew then what is entropy of irreversible
 
Mew
irreversible processes having increasing entropy/disorderness
e.g. shuffling cards is irreversible and leads to increased disorder
 
Always ??
 
Mew
1:53 PM
Moving a card from the top of the deck to the bottom of the deck however is reversible
 
@Mew how it is irreversible
 
Mew
@koolman with a large enough deck shuffling cards is always irreversible
because the probability of maintaining order again through shuffling becomes 0 as the number of cards in the deck approaches infinity
 
How can we decide it is reversible or irreversible
 
Mew
By observing entropy
e.g. mixing a red and blue solution
is irreversible
 
Yes
 
Mew
1:55 PM
because the solution is never going to seperate back into the red and blue solution
because entropy has increased by mixing
and entropy will never decrease
 
Yeah
 
Mew
Now one could try and send in a mini creature to try and manually seperate each atom
 
So in no case the entroph can decrease
 
Mew
but this costs energy and ultimately will increase entropy outside the system
@koolman correct
 
@Mew i see
 
Mew
1:56 PM
Total entropy ALWAYS Increase
3
and NEVER decreases
 
rob
@koolman In reversible processes, the reaction can proceed in either direction. I have an example, but to tell you about it I have to correct an error in the image you posted earlier
38 mins ago, by koolman
user image
 
What error @rob
 
rob
Your image says that S(gas) >> S(liquid) > S(solid), which is a good way to think about things, but an oversimplification.
That suggests there's some intrinsic entropy to each of those phases that you can measure. But actually, the entropy associated with each phase depends on its temperature.
 
Ohhkk
 
rob
A really cold solid has less entropy than a solid that's about to melt, and so on. Make sense?
 
2:03 PM
,yes
 
Mew
@koolman now that you understand entropy I have a challenge question for you, are you ready?
 
Yup
 
rob
So the trick is that the melting point is the temperature where the entropy in the solid phase is the same as the entropy in the liquid phase.
 
Mew
Ok, @koolman here goes: Assume that ice has a lower entropy (more ordered) state than water. Given that entropy never decreases, how is it possible that water can freeze to ice?
 
rob
Below that temperature, the solid is the higher-entropy state, which is why a cooled liquid spontaneously freezes.
 
2:04 PM
@rob Nice point
 
rob
@Mew you are reading my mind :-)
And that's my favorite example of a reversible reaction: a liquid-solid mixture that's just at the melting/freezing temperature.
 
Ice has more entropy
 
Mew
@koolman no
 
rob
It's not the case that freezing and thawing don't happen --- it's that, at the melting temperature, they're equally likely.
 
Mew
it is a more ordered state
 
2:06 PM
hello everyone
 
Mew
@koolman the solution is, is that when water turns to ice, it looses heat to the outside world. Thus the outside world is gaining entropy while the water is losing it
 
thoughts on this question:
2
Q: Demonstration of the existence of a scalar potential for a conservatice force

Élio PereiraMathematically a vector field, $\vec{F}$, is conservative if: $$\oint_{\gamma} (\vec{F}.d\vec{l})=0$$ Physically, the integral is the same as the work done by a force $\vec{F}$ on a body in a closed path. I intend to demonstrate mathematically that a conservative force assumes a scalar potentia...

it seems like a good question, but it might also be classified as homework.
 
Mew
@koolman the overall effect is that the TOTAL entropy of the universe is tsill increasing even though the entropy of the water/ice has decreased
 
Oh i see
Nice question
 
Mew
ty
 
2:08 PM
@rob yeah
@Mew ty too
 
Mew
Hi @heather
 
@Mew, hello
 
Mew
that's a tough one I think it definetly is suitable for the physics.qandaexchange tho
 
yeah
speaking of physics qandaexchange, any new updates?
I've been keeping an eye on the review queue and recent questions list
 
Mew
ty
been busy tho
hopefully can do some stuff on it this weekend
 
2:14 PM
sounds great =)
 
Can anyone help me in this
0
Q: Dependence of entropy of system and surroundings

user135482I read in my chemistry book that the entropy change of a system's surroundings is path dependent while the entropy of the system is state dependent. I don't understand what it means by this. How can entropy be dependent on two different things?

 
Grammar tip: It's "help me with this", not "in this".
 
@ACuriousMind ok
 
@koolman You need to distinguish more carefully between the entropy of the system and that of the surroundings and read the text again.
 
Ohk
 
2:25 PM
what's wrong with this latex code?
\lim_\limit{x\rightarrow 9}\frac{\sqrt{x}-3}{x-9}= \lim_\limit{x\rightarrow 9}\left(\frac{\sqrt{x}-3}{x-9}\right) \left(\frac{\sqrt{x}+3}{\sqrt{x+3}\right) = \lim_\limit{x\rightarrow 9} \frac{x+3\sqrt{x}-3\sqrt{x}-9}{(x-9) (\sqrt{x}+3}=\lim_\limit{x\rightarrow 9}\frac{1}{\sqrt{x}+3} =\frac{1}{\sqrt{9}+3}=\frac{1}{6}
 
lol, how are we supposed to tell that from reading it? :P
 
I don't know, I had hoped someone could spot some gaping error =P
 
Well, it would be more useful if you gave the error TeX spits out
else I have to start it myself and see what it says to have a chance to debug that+
But
wait
 
nevermind, figured it out
missing close brace
 
is \lim_\limit correct syntax?
Why would you do that?
 
2:28 PM
I thought it was...
like to move the expression under the limit operator
$\lim_\limits{x\rightarrow 3}$
 
Yeah, I seem to remember that should be \lim\limits_ but if it compiles then I'm wrong
 
$\lim\limits_{x\rightarrow 3}$
your method works, yeah
okay, I'll try fixing that as well
thanks!
 
Also, the expression is automatically moved under the limit in display mode, and you shouldn't do that inline because it makes the column absurdly wide
@heather Well, if both compile, then there's nothing to fix
 
@ACuriousMind, no, \lim_\limit is wrong
$\lim_\limit{x\rightarrow 3}$
I switched it to \lim_\limits{x\rightarrow 3}
which works
and so does yours
 
Ah, I see
 
2:34 PM
and now it compiled =)
 
 
1 hour later…
3:57 PM
Hm, what on earth is the tag as opposed to the tag for that's not covered equally by ?
 
the former is the technique, the latter is the technology.
 
@BalarkaSen Edited :P
 
You just ruined my troll-attempt. C'mon.
 
lol
@ACuriousMind, those two tags seem to be distinct enough, but all three seem to be meta-tags
 
4:09 PM
@heather I don't agree that they're meta tags, they do relate to the content in the question. I wouldn't find a similar tag like "theoretical-physics" particularly useful, but that's because the volume of experimental questions we get is rather low, so it's nice for the people interested in them to be able to track them with a single tag when they appear.
 
I'm not sure having a tag like and nothing else on the question tells you very much, just like - you have no clue what the question is actually about.
 
Yeah, meta tags are things like or which describe the type of question, rather than the subject which it asks about
@heather It's a rare question where the tags actually tell you what the question is about.
 
@heather It's a very broad subject classicification, but it is a subject classification, hence no meta tag.
Meta tags are those that do not relate to the subject area of the question at all
 
@ACuriousMind, hmm, okay, that makes sense.
nevermind, then, sorry
 
Nothing to be sorry for
 
4:15 PM
but then, returning to your original comment, how do you think and are not distinct?
 
Well, I have trouble seeing what exactly it's supposed to mean. Can you give me an experimental-physics question that should be tagged neither of those two tags? Is it just a tag for everything that's not about technoligy?
The tag description is garbage and doesn't tell me anything
no offense to @dmckee who wrote it intended :P
 
well, my thought would be the technology tag would go on something with a specific technology to use, like "do I need a turbo-molecular pump or a oil pump for this experiment", the technique tag would go on something about implementing a specific technique, almost like recreating an experiment or experiment design, and the overall tag might go on something like analyzing whether results from an experiment make sense, or something along those lines
 
anybody knows how to assign names to aldoses?
I have confusion b/w + -
 
What's an "aldos"?
 
aldose*
monosaccaride
It is a chem topic actually
 
4:21 PM
Does this look like the chemistry room? :D
 
people here are multi talented :P
 
The only chemist here is @JohnRennie and he appears to be hibernating currently
At least, I didn't see him post his lunch today
 
try periodic table:

 The Periodic Table

Haikus are awesome / Chemistry's even better / So pull up a chair
 
Today's lunch was rice pudding, which isn't very photogenic.
 
never heard rice pudding described as much of anything, let alone not photogenic before =P
@ACuriousMind, does that difference make any sense, or no?
 
4:26 PM
@heather I'm not sure I'd tag a question about analyzing the result as "experimental-physics" in the first place, but it depends on how exactly the question is written. (E.g. "I have this data and want to fit this function to it" is a question about analysing experimental results, but I'm not sure what's what the tag is intended for)
 
okay
I'll keep thinking
 
@YashasSamaga Sadly I know nothing about the stereoisomerism of aldoses. I'd follow Heather's suggestion and try the Chemistry SE chat.
 
I don't know where to ask in chem chat :D
I assume that those signs indicate the direction of rotation. If that is true, then I am going to bed angrily becaz I will have to commit those to memory.
 
@YashasSamaga, just click on the link I posted and ask your question, nothing more to it
 
Unlike, D & L system where there is an easy way to remember
oh wait
That name is like "The h bar"
we dont take about planks constant
general chat -_-
 
4:29 PM
what?
 
I meant, the title was misleading :P
I thought The Perodic Table was for talk about the table itself
 
oh, okay =) nope, its the general chat
 
just realized that it is a [some word] title
 
"The h bar" is a pun on it being like a bar (people gather there), and for physicists. "The Periodic Table" is a pun about it being like a table (people gather there), and for chemists.
 
fyi, it is planck
 
4:31 PM
lol
 
not plank
=P
 
I guess the chemists got the short end here, I'd rather be at a bar than at a table
 
well, unless you are under 21 =P
or 18, or whatever
as soon as I think I'm done typing up my calc notes, I notice a new problem
 
For discussion of Plank's constant try here
7
 
@JohnRennie, lol =D
 
4:34 PM
@heather 16, I'm German :P
@JohnRennie ::slow clap::
 
@ACuriousMind, well, I'm underage no matter which of those 3 ages you pick, so =P
 
That's my Black Friday joke. It was a reduced price special.
 
(::shakes head::) (::slow clap::)
oh, I gotta bug my dad (once he wakes up) to see if we can go to the bookstore
 
What do you get if cross a vampire with a robot?
 
I'm keeping my eye on this great abstract algebra book
@JohnRennie, what?
(::prepares to wince::)
 
4:39 PM
NosfeR2-D2
3
 
One part of me wants to groan, the other wants to point out they're called droids, not robots in Star Wars
 
okay, I don't get it..R2-D2, I know, and yeah, thats a droid, specifically an astromech droid, but what's the Nosfe part?
 
Nosferatu
 
(::winces anyway::)
who now?
a german horror film
geesh
(::winces again::)
 
@heather Not only that, nosferatu is generally a synonym for "vampire"
 
4:41 PM
oh, okay
 
Nosferatu is great
 
I can see I have to work on my routine some more.
 
@JohnRennie, yep =P
 
Although in some worlds, nosferatu are a subset of vampires, or slightly different things, it depends on the writer
 
hmm, i want to share this latex doc with you guys to see what you think, but I don't have dropbox...
 
4:47 PM
drop the code into sharelatex?
Or put it on github?
 
github, good idea, one moment
 
@heather page not found
 
@ACuriousMind, weird... I made it a secret gist, but I've shared links to secret gists before and they've worked.
do i need to make it public?
 
I have no idea how github works, so no idea
 
^is that working?
 
4:57 PM
No
 
page not found
 
darn
 

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