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6:22 AM
0
Q: Molar Enthalpy change

harambeA Gas (Cv, m =5/2 R) behaving ideally was allowed to expand reversibly and adiabatically from 1 litre to 32 litre. It's intial temperature was 327°C The molar heat enthalpy change ( in j/mol) for the process is My attempt From polytropic equation. $C_v$=R/ $\Gamma-1$ Solving this gives me ...

Can somebody tell me why I was downvoted here and I am getting less responses?
 
 
1 hour later…
7:51 AM
Question looks homeworky
 
 
3 hours later…
10:31 AM
3
A: What is the difference between hydrogenation in presence of platinum and nickel catalyst?

Nuclear ChemistTwo main points. Firstly, there is an error in the diagram in the question. A hydrogen is missing from the product formed in the Y branch. Secondly, the properties of platinum and nickel are a bit different. One of the key differences is the strength of a $\ce{M-CH3}$ bond. The bond dissociation...

It's a good answer
Deserves more upvotes
This must be the first time ever that I got a good answer after I bountied a question
 
 
3 hours later…
1:26 PM
I've recently been reviewing some high-school thermodynamics, and I've come across a relation that's bugging me...
According to the (non-authoritative) textbook, the relation ΔH = ΔU + (Δn)RT is supposed to be valid when dealing with ideal chemical reactions (which are conducted at constant temperature and pressure).
It was derived this way:
> ΔH = ΔU + Δ(PV)
> Since PV = nRT, we get
> ΔH = ΔU + Δ(nRT)
> And since 'R' and 'T' are constant for an ideal chemical reaction, we get:
> ΔH = ΔU + (Δn)RT
My issue here, is that if temperature is constant, isn't ΔU necessarily zero?
What am I missing?
(@Loong @Mart @ortho can you give this a look?)
 
@paracetamol Why do you think so?
 
2:02 PM
6
Q: Can the change in internal energy be nonzero if temperature is constant?

SudhanshuI have learnt that internal energy, $U$, is a state function and it only depends on temperature... So if $\Delta T = 0$ then $\Delta U = 0$. However when I was studying exothermic and endothermic reactions it was written in my textbook that at a constant temperature and pressure, $\Delta U$ is n...

 
2:26 PM
@Loong Ah my bad, I was thinking of ideal gas expansion/compression >_<
@orthocresol Yep, I've seen your answer before O:)
I get my mistake: I was thinking of ideal gas processes (compressions/expansions) while dealing with a chemical reaction
Thanks, to the both of you! :D
(@Mart I'm cool with it now, sorry for having pinged you) O:)
 
3:07 PM
@orthocresol (1R,2S)-1-fluoro-2-methylcyclopropane and (1S,2R)-1-fluoro-2-methylcyclopropane are not enantiomers?
 
oops
read too fast..
 
ah, okay
 
thanks
that should be corrected now... :/
 
 
2 hours later…
4:45 PM
1
A: What is the difference between hydrogenation in presence of platinum and nickel catalyst?

orthocresolFirst of all, I should clarify that hydrogenation of epoxides does not always proceed with such predictable regioselectivity. Often it depends on the substituents present, as well as their relative configuration (for example, cis/trans for 2,3-disubstituted epoxides).[1] In Reaxys I find no reco...

That answer just put me in a rather awkward position
Its been a while since I saw such high quality content, the bounty is yours once the period ends. — Avnish Kabaj 6 hours ago
Two answers with a lot of effort put into
For a homework question
@paracetamol looks like you have a lot of competition ;)
 
5:18 PM
well, it's a problem when the Q is false and the A tries to rationalise a false statement (quite admirably, nonetheless)
 
5:54 PM
just to be clear, I don’t blame either asker or answerer (although it’s always worth checking the facts before answering), the blame here lies squarely on whoever set that question, knowing that they are teaching something which is at best unreliable and at worst plain wrong to students who don’t know better
questions should always be based on facts, not on some made-up reaction conveniently designed to illustrate whatever concept somebody wanted to illustrate
2
 

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