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Aqa chem 4/ chem 5 june 2016 thread

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Original post by Parallex


@Aerosmith

Explain to me how this is any different to the question. You're provided with enthalpy of formation values and asked to work out the standard enthalpy change of the following reaction exactly as we did.

Just telling you now, there's absolutely no diving in the mark scheme.


Na isn't in its standard state so formation of 1 mol would not be required. Do you now see the logic?
I put increasing SA would increase emf :frown:

ALL SETTLED- You did not need to divide by 2.

THE END of that
Original post by Darthsion100
I got something like 2328 KJ Mol-1 at first, then I halved the atomisation of oxygen to get 2404, but I think the original answer of 2328 was correct, because atomisation is for one mole, and you got 1 mole of O


oh **** yeah ur right, ah well should only be one mark right?
Original post by Suits101
I got that quote from the internet... The top thing that comes up when when I googled standard enthalpy change? Lol.

Well I put kJ/mol so it should be right if what you say is right regardless. :smile:


No it wont be right, because you have divided your enthalpy by 2 and I presume your entropy by 2 - you can expect to drop 2/3 marks.

Next time don't take to TSR trying to tell the 95% of people who didn't get your answer that they are wrong, causing unnecessary stress for people.
Was Gibbs free worth 3 marks?

Also can anyone confirm for MgCl2 solubility one:

Solubility decreases
Forward reaction is exothermic
Equilibrium shifts left to oppose increase in temperature
Original post by Aerosmith
Na isn't in its standard state so formation of 1 mol would not be required. Do you now see the logic?


No.
how many marks do you lose for not converting degrees to kelvin?
Original post by Parallex
No.


I think you're just a stubborn nerd who can't accept that it was perfectly fine to divide by 2 and work it out
Original post by j5994
oh **** yeah ur right, ah well should only be one mark right?


Lets both just prey :/
Original post by Suits101
It came up!!! :smile: :smile:


wtf is the chelate effect?
Original post by Aerosmith
Na isn't in its standard state so formation of 1 mol would not be required. Do you now see the logic?


I'm sorry, with all due respect aerosmith, that comment (plus perhaps most/all of your previous comments you've written in this discussion) is just absolute nonsense.

Na isn't in its standard state? Ok... isn't that why it's delta H value isn't 0 then?

I'm sorry, to be honest I've got no idea what 'logic' you refer to, but long story short Parallex has used an absolutely valid reference to a question and there's nothing that prevents comparison of that question with the one in our exam
Original post by Suits101
Was Gibbs free worth 3 marks?

Also can anyone confirm for MgCl2 solubility one:

Solubility decreases
Forward reaction is exothermic
Equilibrium shifts left to oppose increase in temperature


Solubility one- AGREED :smile:
Original post by Aerosmith
I think you're just a stubborn nerd who can't accept that it was perfectly fine to divide by 2 and work it out

So right I can't wait for people to see the paper again because it asked for delta Hf
Original post by Suits101
Was Gibbs free worth 3 marks?

Also can anyone confirm for MgCl2 solubility one:

Solubility decreases
Forward reaction is exothermic
Equilibrium shifts left to oppose increase in temperature


YES! I got this, but people were telling me it's wrong. I think I've dropped 3 marks in total, I don't want a CE and to make it 6!!
Original post by RME11
No it wont be right, because you have divided your enthalpy by 2 and I presume your entropy by 2 - you can expect to drop 2/3 marks.

Next time don't take to TSR trying to tell the 95% of people who didn't get your answer that they are wrong, causing unnecessary stress for people.


Drop 2 marks if its wrong.

I always write what I have done and I said I BELIEVE that's what you do unless I am certain, you can check my posts.

I have never said that's the proper way to do it because of that reason, and I don't want to argue with you (especially because I have a final exam tomorrow and I don't see the need).
Reply 2835
Avatar for Ohnis
Ohnis
2
Jesus people, it's chemistry not game of enthalpy changes
Do you divide by 2 or not this is doing my head in now
Original post by Spectral
I'm sorry, with all due respect aerosmith, that comment (plus perhaps most/all of your previous comments you've written in this discussion) is just absolute nonsense.

Na isn't in its standard state? Ok... isn't that why it's delta H value isn't 0 then?

I'm sorry, to be honest I've got no idea what 'logic' you refer to, but long story short Parallex has used an absolutely valid reference to a question and there's nothing that prevents comparison of that question with the one in our exam


To be honest with you, I think it's poor wording on AQA's part and so both should be accepted
Reply 2838
Avatar for gh2
gh2
1
For the dividing by 2, I was looking at the question in the exam trying to figure out whether it was necessary or not! I think that if answers are given as for example: -189 kj for the enthalpy change for the reaction then that's fine, and if given as -94.5 kj mol-1 that's also fine. Both are the same it's just the units that change and I think if you changed units depending on your answer you should get the marks. Agree?
Original post by Aethrell
oh for ****s sake, completely forgot


Are we sure it said under standard conditions?

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