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# AQA Chemistry C3 - Unofficial Mark Scheme

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1. (Original post by Fr3dg)
Here is the bond energy once and for all:

ethanol + oxygen-->carbon dioxide + water
CH3CH2OH + 3O2 --> 2CO2 + 3H2O

on the left there are:
5*H-C bonds (each with an energy of 413) which totals 2065
1*C-C bonds at 347
1*C-O bonds at 358
1*O-H bonds at 467
3*O=O bonds (each with an energy of 495) which totals 1485
the total left hand side energy is the sum of these at 4722

on the right side there are:
4*C=O bonds (each with an energy of 799 [for CO2]) which totals 3196
6*O-H bonds (each with an energy of 467) which totals 2802
the total right hand side energy is the sum of these at 5998

4722-5998=-1276
it is left as a negative but a positive answer is fine at GCSE
but the next past said that the reaction was endothermic ah im confused now. everyone i asked also got 212J ah
2. (Original post by Fractite)
Scum is what I wrote.
Thank you! I wrote that too
3. (Original post by elifgecer)
but the next past said that the reaction was endothermic ah im confused now. everyone i asked also got 212J ah
The next part said that the reaction was exothermic - it was a combustion reaction (which always gives out heat if you think about it lol.)
4. (Original post by Fr3dg)
Spoiler:
Show
just to say, if you wrote the OH together it could be wrong, since AQA said "complete the diagram in displayed formula" which requires all of the bonds to be shpwn, wether or not the markers will enforce this is unkown to me, but ever since i got marked down for it in a mock i make sure to check that i display all the bonds
Ah hoping I'll get away with it!

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5. (Original post by Fractite)
We had a specific heat capacity question (work out energy transferred) and the answer was 3444J.
Was that 100% still right because I still don't get it? I did 0.8x4.2x16.4 how many marks do U think for this?

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6. (Original post by blueribbons99)
Was that 100% still right because I still don't get it? I did 0.8x4.2x16.4 how many marks do U think for this?

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You used the correct formula and sort of the correct numbers. So, 2 marks (out of 3) maybe?
7. Arghhh I put the methane one as cows cause I couldn't think of anything 🙈🙈🙈🙈🙈
8. Guys I think if we got 212KJ then we were sitting further additional science not C3 like on this thread.
9. (Original post by elifgecer)
but the next past said that the reaction was endothermic ah im confused now. everyone i asked also got 212J ah
first of all, obviously this reaction is exothermic, even though im 100% said it anyway in the test, its a combustion reaction, these are used to make fire, and heat, its pretty clear they are exothermic, since this heat is the energy that is released by the reaction.
10. (Original post by Fr3dg)
Spoiler:
Show
just to say, if you wrote the OH together it could be wrong, since AQA said "complete the diagram in displayed formula" which requires all of the bonds to be shpwn, wether or not the markers will enforce this is unkown to me, but ever since i got marked down for it in a mock i make sure to check that i display all the bonds
wait, were the two carbons given in the question, thats what i cant remember
11. (Original post by panic!intheexam)
Guys I think if we got 212KJ then we were sitting further additional science not C3 like on this thread.
what was your question? as in the one on the further additional paper?
12. (Original post by Fractite)
You used the correct formula and sort of the correct numbers. So, 2 marks (out of 3) maybe?
Okay hopefully!! Thank you(:

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13. I'm also pretty sure there was no specific heat capacity q in the further additional paper either?
14. (Original post by greenapple10)
wait, were the two carbons given in the question, thats what i cant remember
yeah, they were already given.
we just had to fill out the functional group.
15. Could anyone please upload a picture of what the energy diagram should look like?

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16. What is the difference between further additional and triple anyway?
17. Hey, for the methane question I knew methane was natural gas but rather than write 'natural gas', like most people here did, I wrote 'the atmosphere', do you think this is okay or wrong? I also wrote cow farms above it seeing a small cows produce methane.
18. (Original post by Fr3dg)
what was your question? as in the one on the further additional paper?
Something with methane in it and an oxygen with three bonds I think
19. Can i ask where the division came from? for the speific heat capacity question you only had to multiply
20. (Original post by blueribbons99)
Could anyone please upload a picture of what the energy diagram should look like?

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