Chemistry Predictions/Thoughts (1 Viewer)

[carrotlover123]

wait guys, do ur exam invigilator tell yall to add an exam row for the carbonylic acids for the last question, like 9-13 ppm?

oh shit guys, i just looked at the exam paper on nesa and the paper that we had to do the exam did not include the last row for the 2nd last question and the invigilator told us to add that. did anyone else experience this or did our school just have these papers

 

[C2H6O]

oh shit guys, i just looked at the exam paper on nesa and the paper that we had to do the exam did not include the last row for the 2nd last question and the invigilator told us to add that. did anyone else experience this or did our school just have these papers

no nesa fkd up as usual
cant even rail us correctly

 

[BionicMango]

It happened in 2024, and in 2023 if I remember correctly. It’s normal now lol

 

[Luca26]

oh shit guys, i just looked at the exam paper on nesa and the paper that we had to do the exam did not include the last row for the 2nd last question and the invigilator told us to add that. did anyone else experience this or did our school just have these papers

The question was harder without the added row, as you then needed to recognise that the carboxylic acid H would not give a signal in the alcohol range

 

[Luca26]

do u think i'll lose marks in the second last question for saying the base peak was due to the cooh- bc i had no clue and i thought i would have mention the base peak?

Note that the NIST spectrum (https://webbook.nist.gov/cgi/cbook.cgi?ID=C79094&Mask=200) has the base peak as the molecular ion but still has 28 and 45 as having strong intensity.

The Doc Brown spectrum as the base peak clearly at 28 (https://www.docbrown.info/page06/spectra2/propanoic-acid-ms.htm) with markedly less intense peaks at 45 and for the molecular ion. This is similar to the PubChem MS too (https://pubchem.ncbi.nlm.nih.gov/im...9,29.0:83.51,74.0:69.93,27.0:59.78,45.0:49.64, linked from https://pubchem.ncbi.nlm.nih.gov/compound/Propionic-acid#section=GC-MS).

I don't think correctly predicting the base peak is a reasonable expectation for HSC students.

 

[m_avi]

i was doing this worksheet and found this. Specifically looking at part e, i just remember there was a similar question in the hsc.

 

[C2H6O]

View attachment 50483

i was doing this worksheet and found this. Specifically looking at part e, i just remember there was a similar question in the hsc.

WTF SO EQUILIBRIUM DOES SHIFT???????
(Just to be clear those answers say i (eq position) shifts <— but ii no change in value of Keq, which was what most people put?)
IS THERE HOPE??

 

[m_avi]

WTF SO EQUILIBRIUM DOES SHIFT???????
(Just to be clear those answers say i (eq position) shifts <— but ii no change in value of Keq, which was what most people put?)
IS THERE HOPE??

yeah i think that was the trippy part. The minuscule pressure increase causes it to shift to the left. But that shift has no effect on the temperature???

 

[m_avi]

however i did find some people saying that adding argon causes the Average kinetic energy of the system to increase or smth and that affects temperature idk tho

 

[C2H6O]

yeah i think that was the trippy part. The minuscule pressure increase causes it to shift to the left. But that shift has no effect on the temperature???

Yeah because it shifted in the exothermic direction which would cause more heat to be produced

however i did find some people saying that adding argon causes the Average kinetic energy of the system to increase or smth and that affects temperature idk tho

Yeah that’s Gay Lussac’s law P/T=k
Idk if that’s what they wanted as well but I didn’t have enough space after explaining the eq shift so I didn’t bother, hope that wasn’t the main reason for the temp shift.

So do we think the answer is there is a shift or not after argon?

 

[nowomansland]

Yeah because it shifted in the exothermic direction which would cause more heat to be produced



Yeah that’s Gay Lussac’s law P/T=k
Idk if that’s what they wanted as well but I didn’t have enough space after explaining the eq shift so I didn’t bother, hope that wasn’t the main reason for the temp shift.

So do we think the answer is there is a shift or not after argon?

lets just wait for the marking guidelines i lit have no clue atp

 

[Trial&Error]

View attachment 50483

i was doing this worksheet and found this. Specifically looking at part e, i just remember there was a similar question in the hsc.

I hope this is right. I had a nagging feeling at the back of my mind that I read somewhere eq doesn't shift but I wasn't sure so I wrote "it slightly shifts" I just hope they accept it cause it was worth a whole 4 marks.

 

[Average Boreduser]

Yeah because it shifted in the exothermic direction which would cause more heat to be produced



Yeah that’s Gay Lussac’s law P/T=k
Idk if that’s what they wanted as well but I didn’t have enough space after explaining the eq shift so I didn’t bother, hope that wasn’t the main reason for the temp shift.

So do we think the answer is there is a shift or not after argon?

gay lusaacs doesn't work in context of the question

 

[C2H6O]

gay lusaacs doesn't work in context of the question

why they added more moles of gas which increases pressure cause rigid container then increase temp

 

[C2H6O]

ohh wait cause eq shifts?

 

[BionicMango]

WTF SO EQUILIBRIUM DOES SHIFT???????
(Just to be clear those answers say i (eq position) shifts <— but ii no change in value of Keq, which was what most people put?)
IS THERE HOPE??

that's the thing, it can't change if keq doesn't change and if concentrations are still equal

 

[BionicMango]

why they added more moles of gas which increases pressure cause rigid container then increase temp

PV=nRT
n increases, P increases, T constant, no?

 

[C2H6O]

that's the thing, it can't change if keq doesn't change and if concentrations are still equal

bruhh
so youre saying if neither volume nor temp nor moles of reactive species changes in a gas eq there can be no change in position no matter what else you do? fk that actually makes sense

 

[BionicMango]

Yeah exactly

 

[wizzkids]

2025 HSC Chemistry, Question 29.
This is another badly drafted question. The examiners left out one key fact - was the argon added under isothermal conditions or adiabatic conditions? That is why you are all speculating about Avogadro' Law of gases and Gay Lussac's Law and all that other stuff. It's good that you are asking these questions because it shows you have extensive knowledge of Chemistry.
The addition of argon to the reaction vessel of fixed volume causes no change to the K value and no change to position of equilibrium. The concentrations of the NO₂ and N₂O₄ are not changed by the addition of argon. We should use their partial pressures as a measure of their concentrations, and the partial pressures remain the same so the concentrations are the same. Therefore provided the argon is added under isothermal conditions (not adiabatic conditions) there will be no change of temperature.