Thermodynamics

YUSUF HASAN

Mar 18, 2019 12:26

I mean.. What I get from his question... Is that why HCl is not as strong as it usually is in standalone aqueous form rather than when it is mixed with HF.. So here of course dissociation of HCl will go down due to (whatever small) dissociation of HF occurs... Common ion effect..

PolarBear

@Abcd He said that HCl is stronger than HF

Abcd

YUSUF HASAN

@PolarBear No.. I think we meant that HCl becomes weaker in HF

Abcd

Doubt @PolarBear @YUSUFHASAN

PolarBear

@YUSUFHASAN Oh, now I get it

Abcd

Mar 18, 2019 12:27

@YUSUFHASAN I dont think Common ion effect is right explanation.

Dante

@Abcd I never understood this questions properly, though being a adv 2017 ques it had many solutions online. It was after looking at this ques I lost confidence in thermodynamics X

Abcd

$\ce{H2O(l) (1 bar, \pu{373 K}) -> H2O(g)(1 bar, 373 K)}$

YUSUF HASAN

@Abcd I mean.. Common ion effect weakens the dissociation of both acids simultaneously,right? Simulataneous equilibrium and all that..?

Abcd

Write $\text{signum}(\Delta G), \text{signum}(\Delta S)$ for this reaction:

1 min ago, by Abcd

$\ce{H2O(l) (1 bar, \pu{373 K}) -> H2O(g)(1 bar, 373 K)}$

@YUSUFHASAN @PolarBear @Dante This easier one as well pls^

@Dante Well, rest of the thermodynamics archive is very easy. Dont get disheartened by 1 or 2 questions.

PolarBear

@Abcd (Okay I don't know that answer but just trying on my getting answer by hook crook method is it (A)?)

YUSUF HASAN

Mar 18, 2019 12:31

H-bonding is there in HF... But it is quite weak in solution phase.. So i would say that common ion effect is good enough here

Dante

I see

Abcd

@PolarBear Crkt

Dante

OP says HCl + HF <-> H2Cl+ + F-

PolarBear

(Whoo, lemme think then btw I found out the answer by dimensional analysis)

Dante

So it's not a typo

Abcd

Mar 18, 2019 12:33

@PolarBear All answers are in bar!! How did you use Dimensional

Dante

@Abcd Calculation for that question is very easy, it's direct XD

It's just difficult to understand

PolarBear

@Abcd Not exactly.

Abcd

Answer 2nd question you all.

YUSUF HASAN

@Abcd Where is the 2nd question?

Abcd

@YUSUFHASAN See signum

@PolarBear I tried using : $\Delta G^o = -RT\ln(K_p)$

PolarBear

Mar 18, 2019 12:35

(deleted because you shouldn't do questions that way lol)

YUSUF HASAN

@Dante Proves my point.. Common ion effect is surely randomising stuff here.. Thats why that equilibrium exists

Abcd

lol$^\infty$

@YUSUFHASAN I still think its because of low polarity of HF

@YUSUFHASAN Who is stronger Acetic or HF

Dante

Maybe you both could google for a confirmation?

I did but wasn;t satisfied

Abcd

11

Q: Acidity of hydrochloric acid in acetic acid

A question asked to find the $\mathrm pK_\mathrm a$ of $\ce{HCl}$ in acetic acid. The equation of $\ce{HCl}$ disassociating in water is: $$\ce{HCl + CH3COOH \leftrightharpoons CH3COOH2+ + Cl-}$$ I predicted that the $\mathrm pK_\mathrm a$ should be higher as acetic acid is a weaker base than wat...

Thats in acetic

PolarBear

So I opened my book and I have started abcd's question

I don't even remember solving thermo

Abcd

Mar 18, 2019 12:36

Because of low polarity.

@PolarBear 2nd question first please!!

Thats 1 second question.

7 mins ago, by Abcd

Write $\text{signum}(\Delta G), \text{signum}(\Delta S)$ for this reaction:

7 mins ago, by Abcd

1 min ago, by Abcd

$\ce{H2O(l) (1 bar, \pu{373 K}) -> H2O(g)(1 bar, 373 K)}$

@AdvilSell Are you online

PolarBear

I meant starred* when I was little in class 11

Starred* not started*

(See that's what I did)

(Not really)

@Abcd delta S is Delta H/T

Abcd

@PolarBear tell answers first

@PolarBear this is so hard!!

PolarBear

You didn't give delta H

@Abcd Not hard

I did it in seconds xD

Abcd

@PolarBear question didnt give

PolarBear

dG is VdP that's the only info reqd

Dante

Mar 18, 2019 12:45

Is internal energy of solids dependent only on temp just like ideal gases?

Abcd

@PolarBear But we have to derive it too right? Or did you learn this formula?

Dante

guess not...

YUSUF HASAN

Wait a minute.. Is some info missing?

Abcd

@YUSUFHASAN Which ques?

PolarBear

@Abcd latent heat 40.8 we know

YUSUF HASAN

Mar 18, 2019 12:46

@Abcd U can derieve it via thermodyanmic sqaure.. dG=VdP-SdT

Abcd

Guys signum just means give the signs.

PolarBear

I think that's what we will use

YUSUF HASAN

@Abcd The second one.. R u giving us the enthalpy?

PolarBear

@Abcd Oooh didn't know didn't notice either

Abcd

@YUSUFHASAN C my latest message.

PolarBear

Mar 18, 2019 12:47

So you are talking about system or surrounding or whole?

Abcd

Also sign(0) = 0

@PolarBear Question didnt say anything.

YUSUF HASAN

Oh.. So entropy change sign is.. Positive? For system?

Let's assume it to be system

Abcd

@YUSUFHASAN Right And $\Delta G$?

PolarBear

@Abcd positive

Abcd

@PolarBear wrong

PolarBear

Mar 18, 2019 12:49

Someone had linked a question on SE somewhere or I had just read it

Abcd

@YUSUFHASAN wrong

PolarBear

It's reversible

Abcd

Guys nothing is given in the question.

its IIT 2007 ques

Dante

17 lol

Abcd

No 2007

Dante

Mar 18, 2019 12:50

no 17

Abcd

@PolarBear 373 K is 100 C not room temp

Dante

@Abcd Is there anyway I can bookmark this conversation?

I would like to go through it after I finish thermo from NA

Abcd

@Dante See my instructions to bookmark conversation in PSS to nobodyrecog.

PolarBear

We should have bookmarked the conversation on how to bookmark a conversation that would have made bookmarking easier

Abcd

right

oh Ice has also given d instr.

Jun 27 '18 at 3:07, by Anonymous

@Abcd Go to this chat transcript, there is bookmark on right side of the desktop page. Click on it, then click on your 'start message' and then click on your 'end message'. The whole conversation from the start message to the end message will be bookmarked.

@YUSUFHASAN @PolarBear Why is $\Delta G = 0$ ???

PolarBear

Mar 18, 2019 12:53

It's zero. I said it.

YUSUF HASAN

Oh yes. I didn't see the temperature... And sincd they have given only the forward reaction.. So it will definitely be spontaneous at 100 degree celsius(facepalm, I am stupid)

Abcd

@YUSUFHASAN For spon. $\Delta G = -ve$

PolarBear

It's zero. Zero. Yay. I'm right. I'm right.

It's equilibrium.

I am acting dumb today.

Abcd

Ice give reason

PolarBear

16 secs ago, by PolarBear

It's equilibrium.

YUSUF HASAN

Mar 18, 2019 12:54

@PolarBear They have only given forward reaction in the question.. So u can't assume backward reaction here as far as I think

PolarBear

It seems like I have done all thermo questions.

@YUSUFHASAN No. You can.

That's what you have to think.

Dante

@Abcd Where's chat transcript?

PolarBear

It's an equilibrium we know that.

Abcd

$\ce{P_(white, solid) -> P_(red, solid)}$

Dante

what is chat transcript?

Abcd

Mar 18, 2019 12:55

@Dante Actually

click Room on LHS

Above your gravatar

PolarBear

@Abcd What to do?

YUSUF HASAN

@PolarBear Well.. Then delta G is zero.. So?

Abcd

@PolarBear Is it phase transition or not?

YUSUF HASAN

@Abcd I am saying that since it is not given.. I don't know that whether they want us to consider the back reaction and take it as a phase change

Abcd

@YUSUFHASAN ya exactly

@YUSUFHASAN Question 3 or 2?

YUSUF HASAN

Mar 18, 2019 12:58

@Abcd sign of delta G one

Abcd

@YUSUFHASAN OK I agree with u on that

$\ce{P_{(white, solid)} -> P_{(red, solid)}}$

State if the above reaction is a Phase Transition or Not. @YUSUFHASAN

PolarBear

@Abcd Allotropes aren't phase transitions but we consider them sometimes

Abcd

@PolarBear Say definite answer. yes or no.

PolarBear

Traditionally, no. But yes. I remember my teacher saying that.

Abcd

Lol no but yes.

Say one thing.

What would u write .

PolarBear

Mar 18, 2019 13:00

Yes. I guess. There was an SE question on that too.

Abcd

Yes you are right. But I dont understand how.

YUSUF HASAN

@Abcd In generality,yes it is a phase transition.. But it has two rate constants associated with it.. Suppose you want to talk about only one.. U make a question on that.. Then i will consider that reaction only

PolarBear

Those days when our teacher didn't teach us thermo and we had to learn ourselves. I learnt so much.

1

Q: Is Changing between Allotropic forms a Physical or Chemical Process?

When a substance changes its alloptropic form, is this considered a physical change or a chemical change? Right now, I am thinking that it would depend on what the change was. For example, if graphite was changed to diamond under high pressure, I would say it is a chemical change since new bonds...

crystal-structure solid-state-chemistry allotropes

Abcd

@YUSUFHASAN No this was a JEE question. Not mine.

PolarBear

See the answer.

@Abcd Maybe because I have seen it before so I subconsciously said that.

Abcd

Mar 18, 2019 13:01

@PolarBear its talking about Chemical vs Physical process. Not phase trans as a term for allotrope connversion.

PolarBear

1 min ago, by PolarBear

See the answer.

Abcd

Also, predict sign of $\Delta S$ (I was able to do this :D)

> The conversion of ferrite into austenite is a phase transition, so it should formally be classified as a physical change.

YUSUF HASAN

@Abcd allotropy will be considered a phase change cuz the two reactions(forward and backward) can enter such a state where their rates become equal.. That is...activation energh required becomes negligible... So u can take it at equilibrium

2

Abcd

@PolarBear Standard state has zero enthalpy

not entropy.

PolarBear

I was being dumb

@YUSUFHASAN Nice

YUSUF HASAN

Mar 18, 2019 13:04

That is what answer states..And yes.. Entropy is only zero at zero Kelvin

Abcd

@YUSUFHASAN Which answer r u referring to now??

PolarBear

I think this it is more like p block question

Abcd

Yep.

Think and answer.

Sure?

Wrong!!!

Its less than 0.

Red is more ordered as it is polymeric

YUSUF HASAN

Never mind.. It was deleted.. And no.. Entropy change is ofcourse negative

Abcd

White is haphazard

question was white to red ice

PolarBear

Mar 18, 2019 13:06

Oh, shit (':

I should study CS. Anymore questions?

YUSUF HASAN

Okay.. Seems @PolarBear didnt read the question

Advil Sell

Isn't red more reactive ??

Abcd

No

YUSUF HASAN

No.. Red is polymeric

Advil Sell

due to angle starin

Abcd

Mar 18, 2019 13:07

white is more reactive

PolarBear

@AdvilSell No

Abcd

angle strain in white

YUSUF HASAN

Bro.. White has angle strain

PolarBear

@AdvilSell That's white

Abcd

BTW reactivity is not the right explanation of Entropy!!

It has to do with degree of randomness.

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