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ocr a f325 revision thread

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For that IO3- question did you put that it was oxidised to I- or I2? =S
And on the second page where it said to name the steps, is it just Enthalpy change of .... or do you think you need Standard Enthalpy Change of....?
Reply 4201
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Lysipud
1
What did people do for the entropy question???

Did we have to use the equation ^G = ^H - T^S ??
Original post by Sarangtaec
For that IO3- question did you put that it was oxidised to I- or I2? =S
And on the second page where it said to name the steps, is it just Enthalpy change of .... or do you think you need Standard Enthalpy Change of....?


Just enthalpy will be fine, I expect. And it went to I2 - I think it mentioned that in the question.
Original post by Lysipud
What did people do for the entropy question???

Did we have to use the equation ^G = ^H - T^S ??


You did to calculate ^G. But to work out the entropy of glucose, you had to use ^S = Sum S(Products) - Sum S(Reactants).
Reply 4204
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Raj Kang
Guys the box filling one didn't h2 go smaller and the reactants increase because it says in the question you had to compare it to the kc in the previous question which was 16 or something and when you use 2.00 instead of 3.00 for the reactant kc decreases so equilibrium will shift to the left
Reply 4205
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Lysipud
1
Is there an unofficial mark scheme yet guys??
Reply 4206
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Lysipud
1
Original post by PythianLegume
You did to calculate ^G. But to work out the entropy of glucose, you had to use ^S = Sum S(Products) - Sum S(Reactants).


So for the first part of the question did you do the product - reactants and was it something like -400 something?

Then for the second part you use the ^G equation?? But for the value of ^S do you use the one you calculated for the first question or the one that was already given???
Original post by Raj Kang
Guys the box filling one didn't h2 go smaller and the reactants increase because it says in the question you had to compare it to the kc in the previous question which was 16 or something and when you use 2.00 instead of 3.00 for the reactant kc decreases so equilibrium will shift to the left


No. If H2 went smaller, then I2 also had to go smaller and HI would have to go bigger, which would lead to an increase in Kc (when it should remain constant).
Original post by wakaas
What do other people the grade boundaries wil roughly be???


Unsure, the questions weren't difficult, but time was a big factor I think.

I think it will be about the same, maybe 1-2 marks higher than January 2013, as the difficulty of the paper wasn't too far off.
Original post by Lysipud
So for the first part of the question did you do the product - reactants and was it something like -400 something?

Then for the second part you use the ^G equation?? But for the value of ^S do you use the one you calculated for the first question or the one that was already given???


For the first part, you were given ^S, but not one of the product's entropy, so you had to re-arrange the question to get a positive answer of about 218.

For the second part, you used the value of ^S for the whole reaction - the one they gave you at the start.
Mark scheme?
Original post by FailedMyExams
Unsure, the questions weren't difficult, but time was a big factor I think.

I think it will be about the same, maybe 1-2 marks higher than January 2013, as the difficulty of the paper wasn't too far off.


72/73 for A
67 for B
does anyone remember the values for the Kc question, i just want to reconstruct it and see what i got.
The values like the equilibrium concentrations and the volume
Reply 4213
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516359
12
Don't worry I got my answer.
(edited 10 years ago)
Reply 4214
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MiriamK
Unofficial mark scheme will be posted in a few minutes, folks! (look out for a post from Kat12395)
Original post by randomd_love
Before I get jumped on by mods am I or am I not allowed to post questions from the paper. I have pics of the last question from when I went back to the hall for my coat


U have a freedom mate jst do watever u want :biggrin:
Original post by MiriamK
Unofficial mark scheme will be posted in a few minutes, folks! (look out for a post from Kat12395)


Thank you very much for doing this for us!
Original post by MiriamK
Unofficial mark scheme will be posted in a few minutes, folks! (look out for a post from Kat12395)


You're saying this frm last 15-20 minutes i think
WE HAVE FINISHED THE MARK SCHEME (Finally!)
https://docs.google.com/document/d/1WICd6ufVwBxfVz10_b4Hqd85oSv2FMQTrcll_t5qD0k/edit?usp=sharing
YOU'RE WELCOME!
Reply 4219
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Raj Kang
Original post by PythianLegume
No. If H2 went smaller, then I2 also had to go smaller and HI would have to go bigger, which would lead to an increase in Kc (when it should remain constant).


No your wrong because kc can decrease by increasing concentration of reactants and decreasing the concentration of products it's all in the question

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