AQA CHEM5 A2 Chemistry - 19th June 2013

Reply 1680

SexyAndIKnowIt.

1

In born haver cycle, would you use atomisation or sublimation

Reply 1681

gooner1886

Original post by Jessica-F

Does anyone have notes or know a good site where i can get help with the calculations? i get really confused with some of them.

http://www.thestudentroom.co.uk/showthread.php?t=1288539

Reply 1682

Zytex

Original post by Puffy14

How did you get the chromium one? Can you please write the half equations for that one? :colondollar:

Reduction half equation

Cr_{2}O_{7}^{2-} + 14H^{+} + 6e^{-} --> 2Cr^{3+} + 7H_{2}O

Oxidation half equation

Fe^{2+} --> Fe^{3+} + e^{-}

Need to multiple the oxidation reaction by 6 to cancel out the electrons.

Therefore:
Overall equation:

6Fe^{2+} + Cr_{2}O_{7}^{2-} + 14H^{+} --> 6Fe^{3+} + 2Cr^{3+} + 7H_{2}O

(edited 10 years ago)

Reply 1683

marleyxd

Can anyone help me with this question?

On June 2011 paper, Qa)i) The bond enthalpy one, i don't how the mark scheme says -38?
Bonds broken - Bonds made, when i did it it came out as -76
In the mark cheme they have divided the N2 bond enthalpy by 2 and multiplied the H2 bond enthalpy by 3/2?? Why??

ANYONE?

Reply 1684

jqian

1

Original post by marleyxd

Can anyone help me with this question?

On June 2011 paper, Qa)i) The bond enthalpy one, i don't how the mark scheme says -38?
Bonds broken - Bonds made, when i did it it came out as -76
In the mark cheme they have divided the N2 bond enthalpy by 2 and multiplied the H2 bond enthalpy by 3/2?? Why??

ANYONE?

It says the formation of one mole of ammonia, hence 1/2 N2 + 3/2 H2 --> NH3.

Reply 1685

MrMeep2580

Original post by marleyxd

Can anyone help me with this question?

On June 2011 paper, Qa)i) The bond enthalpy one, i don't how the mark scheme says -38?
Bonds broken - Bonds made, when i did it it came out as -76
In the mark cheme they have divided the N2 bond enthalpy by 2 and multiplied the H2 bond enthalpy by 3/2?? Why??

ANYONE?

the definition of enthalpy of formation is:

the enthalpy change that occurs when 1 mol of a molecule is formed from its constituent elements when they're in their standard states, under standard conditions.

In the question it forms 2 moles so you need to use it to find 1 mol formation

Reply 1686

Melissa.S.

Did anyone else find the June 2012 past paper really difficult??

Reply 1687

marleyxd

Original post by jqian

It says the formation of one mole of ammonia, hence 1/2 N2 + 3/2 H2 --> NH3.

Thanks! I never read questions properly....

Reply 1688

sikhtank27

2

jan 2013 is one nasty paper....personally if you can ace the jan 13 paper, I think you'll be fine for the exam tomaz!

Reply 1689

SexyAndIKnowIt.

1

In a b-h cycle, when you start off with cl2, how to I get this to just cl so it can be ionised. Do I double half whattt

Reply 1690

mcollin1

Original post by sikhtank27

jan 2013 is one nasty paper....personally if you can ace the jan 13 paper, I think you'll be fine for the exam tomaz!

where'd you get the jan 13 from?

Reply 1691

jadealycia

1

Original post by problematic

Hey guys can anyone help me out with this question about cell representations, It's from the Jan10 paper

I find it kind of confusing how the did it in the mark scheme and if someone could talk me through it that would be great

I've attached the pic with the q

Thanks in advance

it just means the cell notation x

Reply 1692

Chris-69

7

For those who have finished all the papers, what type of revision are you doing?

Reply 1693

flyylikejetz

11

What colour is Co(H2O)3(OH)3 after it has been oxidised. In one book it says 'beige' in another it says 'brown' ??

Reply 1694

Beth_L_G

10

Original post by flyylikejetz

What colour is Co(H2O)3(OH)3 after it has been oxidised. In one book it says 'beige' in another it says 'brown' ??

Mark schemes usually say dark brown I think

Reply 1695

jadealycia

1

Original post by SexyAndIKnowIt.

In a b-h cycle, when you start off with cl2, how to I get this to just cl so it can be ionised. Do I double half whattt

when you do the enthalpy of atomisation for Chlorine this should take it from Cl2 to 2 Cl, then when you come to electron affinity you multiply this by 2.

Hope this makes sense

Reply 1696

mulac1

chocolate brown :wink:

-

thats how I remember it .. just go for brown - I highly doubt that will come up anyway :smile:

Reply 1697

mulac1

I hope tomorrows paper is nicer than the biol5 one we had yesterday...
then again I'm sure it will be as chemistry > biology

Reply 1698

Emfasis

Original post by Chris-69

For those who have finished all the papers, what type of revision are you doing?

I'm going through all the papers again :colondollar:

not sure how much good it's doing though since I subconsciously know the answers, other than that I'm reading the AQA book and copying out all of the periodicity, catalyst and transition equations over and over again! :facepalm: