Aqa a2 chem5 19th june 2012
Chemistry exam discussion - share revision tips in preparation for GCSE, A Level and other chemistry exams and discuss how they went afterwards.
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Re: Aqa a2 chem5 19th june 2012Tell me about it bro.(Original post by Matthew692692)
I'd have such a better average if it weren't for ISAs ugh!
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Re: Aqa a2 chem5 19th june 2012Inshallah i can make it in(Original post by shuaib786)
wow 60/60 mashallah. I got 36/60, i got 255/300 in my AS, so my isa has pulled it down. I've firmed Aston for Pharmacy. One of friends has got an offer for Accounting and Finance at Warwick. Its supposed be a good university for Accounting.
Pharmacy is meant to be good at Aston, i had a 2-3 friends go there last yr.
I feel really unprepared for this exam as i still haven't memorised all the colour changes and the reactions that go along with them
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Re: Aqa a2 chem5 19th june 2012give yourself like 2 hours to do it in that will get you most way there, there not so hard, lots of em are the same(Original post by uxa595)
Inshallah i can make it in
Pharmacy is meant to be good at Aston, i had a 2-3 friends go there last yr.
I feel really unprepared for this exam as i still haven't memorised all the colour changes and the reactions that go along with them
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Re: Aqa a2 chem5 19th june 2012Yup, done Cu and Co(Original post by chill543)
give yourself like 2 hours to do it in that will get you most way there, there not so hard, lots of em are the same
Cr seems a little tough. -
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Re: Aqa a2 chem5 19th june 2012ok so I am really finding this question hard....can someone please help.....
calculate deltaHf for propane C3H8, given the following data.
C(s) ..................> C(g) deltaH = 715 KJmol-1
3C(s) + 4H2(g)....................> C3H8 (g)
Bond = C-C C-H H-H
KJmol-1 = 348 412 436
please .......
confused:
Last edited by g00d4u; 16-06-2012 at 11:02. -
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Re: Aqa a2 chem5 19th june 2012Isn't it just bonds broken - bonds formed.(Original post by g00d4u)
ok so I am really finding this question hard....can someone please help.....
calculate deltaHf for propane C3H8, given the following data.
C(s) ..................> C(g)
3C(s) + 4H2(g)....................> C3H8 (g)
Bond = C-C C-H H-H
KJmol-1 = 348 412 436
please .......confused:
So 3x348 + 4x436 - 8x412 - 2x348 = -1204Last edited by LookIt'sPete; 16-06-2012 at 10:27. -
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ΔHf= Σbonds broken-Σbonds formed(Original post by g00d4u)
ok so I am really finding this question hard....can someone please help.....
calculate deltaHf for propane C3H8, given the following data.
C(s) ..................> C(g)
3C(s) + 4H2(g)....................> C3H8 (g)
Bond = C-C C-H H-H
KJmol-1 = 348 412 436
please .......confused:
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Re: Aqa a2 chem5 19th june 2012apparently this is the method:-(Original post by Matthew692692)
ΔHf= Σbonds broken-Σbonds formed
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deltaHf = (3xdeltaH atomistaion (c) + 4xE(H-H) - (2xE(C-C)+8xE(C-H)
= (3x715+4x436) - (2x348+8x412)
= -103KJmol-1
but how????????? -
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Re: Aqa a2 chem5 19th june 2012I think we just have to know the equation and what it stand for:-(Original post by stephie.u3)
do we need to be able to state plancks constant??
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deltaE = hv
energy=plancks contant x frequency.....
correct me if I am wrong someone... -
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Re: Aqa a2 chem5 19th june 2012The specification states: 'Know that the colour arises from electronic transitions from the ground state to excited states. E=hv'(Original post by stephie.u3)
do we need to be able to state plancks constant??
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There is nothing abut being able to state planks consant, I expect they would it give to you if a calculation on this comes up. -
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Oh I'm not sure... Is it a Hess Cycle?(Original post by g00d4u)
apparently this is the method:-
deltaHf = (3xdeltaH atomistaion (c) + 4xE(H-H) - (2xE(C-C)+8xE(C-H)
= (3x715+4x436) - (2x348+8x412)
= -103KJmol-1
but how?????????
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Re: Aqa a2 chem5 19th june 2012(Original post by LookIt'sPete)
Isn't it just bonds broken - bonds formed.
So 3x348 + 4x436 - 8x412 - 2x348 = -1204its a complicated example that might come up because it is using combination of different data, partly mean bond data and atomisation data but what i dont understand is why (C-C) not multiplied by 3 in the second part....(Original post by Matthew692692)
Oh I'm not sure... Is it a Hess Cycle?
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Re: Aqa a2 chem5 19th june 2012Oh yeah, of course, I see. There are no c-c bonds in the reactants but the carbon is in a solid state but needs to be in a gas state for formation. You missed out the enthalpy of atomisation when you posted the question...(Original post by g00d4u)
its a complicated example that might come up because it is using combination of different data, partly mean bond data and atomisation data but what i dont understand is why (C-C) not multiplied by 3 in the second part....
If you mean the second part, as in the C3H8, it's because the structure is H3C-CH2-CH3 so there are only two C-C bonds. -
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Re: Aqa a2 chem5 19th june 2012can someone help me on question 5e(iii) on the jan 20 paper?
http://store.aqa.org.uk/qual/gce/pdf...W-QP-JAN10.PDF -
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Re: Aqa a2 chem5 19th june 2012What value did you get for e)ii)?(Original post by rss.914)
can someone help me on question 5e(iii) on the jan 20 paper?
http://store.aqa.org.uk/qual/gce/pdf...W-QP-JAN10.PDF -
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Re: Aqa a2 chem5 19th june 2012464 K(Original post by LookIt'sPete)
What value did you get for e)ii)? -
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Re: Aqa a2 chem5 19th june 2012Ok, that means the answer is that the reaction becomes unfeasible.(Original post by rss.914)
464 K
This is because delta h and delta s are both negative so if t is higher than what you calculated, delta g will be higher than 0. -
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Re: Aqa a2 chem5 19th june 2012thanks, what would happen if delta h was positive and delta s was negative(Original post by LookIt'sPete)
Ok, that means the answer is that the reaction becomes unfeasible.
This is because delta h and delta s are both negative so if t is higher than what you calculated, delta g will be higher than 0.
or delta h was negative and delta s was positive
