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AQA Chemistry C3 - Unofficial Mark Scheme

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I got 212 for the bond energies question
Original post by BDunlop
Yes that's right, it has to be positive for endothermic reaction


No, they said it was exothermic. So it must be a negative number; it was the same reaction.

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Fr3dg
7
Original post by schoolgsc
I got 212 for the bond energies question


unlucky dude
Original post by schoolgsc
I got 212 for the bond energies question


same, the majority in my school got that.
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AR5
Original post by miamathewss
what was the methane q


natural gas I think
Reply 225
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Fr3dg
7
Original post by greenapple10
can someone confirm weather the question on completing the rest of the diagram was for ethanol or ethanoic acid?


it was ethanoic acid
Original post by Fr3dg
unlucky dude


how did you people got those high numbers exceeding the 1000
Original post by MehdiK24
how did you people got those high numbers exceeding the 1000


You work out the bonds broken (which altogether totalled about 4700 - you have to consider the 2 before a compound means you times it all by 2).
Then bonds formed (totalled 5998KJ).
The answer for the bond question was around 1276 i think. It can be either negative or positive, it asks about energy change and according to previous mark schemes no matter if exothermic or endothermic you dont need to write the sign.
Reply 229
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Fr3dg
7
Original post by Roquebrune2014
Complete the diagram for ethanol can acid should have looked like this when completed:

ImageUploadedByStudent Room1466010500.409435.jpg

(If you wrote the OH attached together, that is also perfectly acceptable)


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Spoiler

how could the bond energy have been a negative value if the reaction was endothermic.... i got 212J and so did pretty much everyone else i asked
Original post by Wisbey
Ethanoic Acid - CH3COOH.


oh right, i remember now, i pretty sure i done that, i cant remember though, i do remember using COOH so yh thanks for clearing it up. Cheers!
Reply 232
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Fr3dg
7
Original post by schoolgsc
I got 212 for the bond energies question


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
Reply 233
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Fr3dg
7
Original post by elifgecer
how could the bond energy have been a negative value if the reaction was endothermic.... i got 212J and so did pretty much everyone else i asked


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
Reply 234
Avatar for Fr3dg
Fr3dg
7
Original post by MehdiK24
how did you people got those high numbers exceeding the 1000


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
Original post by elifgecer
how could the bond energy have been a negative value if the reaction was endothermic.... i got 212J and so did pretty much everyone else i asked


The next question said that the reaction was exothermic, so it had to be negative - but yeah, I think positive answers will slide.
Original post by bod247
Its Rb because in group 1 (alkali metals), the Boiling point and Melting Point decrease as you go down. Rb was the last Alkali Metal so its the lowest Boiling Melting/Point.


it was Fluorine cuz halogens r gases at room temp and F is the most reactive halogen.
Reply 237
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srmed
2
What did people write for that question where it said what solid is produced when hard water reacts with soap? Can't fully remember what it asked
Original post by srmed
What did people write for that question where it said what solid is produced when hard water reacts with soap? Can't fully remember what it asked


Scum is what I wrote.
yh I got that and I practised that a lot in class so Im 100% sure its right

Original post by ThomasSidney1
On the specific heat capacity question I think I got an answer of around 55.104? Didn't you have to do 0.8 x 4.2 x (38.4-22.0) since that was the temperature change?

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