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AQA Chemistry C3 - Unofficial Mark Scheme

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Original post by milolj
Will you lose a mark for saying 1623 rather than -1623?


I GOT -1623 AS WELL! I'm so confused about how so many people have different answers?
Original post by BDunlop
Yes that's right, it has to be positive for endothermic reaction


Which paper were you sitting? It seems like people got different results so maybe some people did triple and some did further additional
Original post by mrtum3000
Corrections:
''Tube B: calcium carbonate produced, solution goes cloudy'' - carbon dioxide makes limewater go cloudy
''How is methane obtained: Cows (?)'' - natural gas
''Element that has low boiling poyint: F'' - Rb is also valid I think

The question was lowest, so it would have to be Rb
Original post by BDunlop
Yes that's right, it has to be positive for endothermic reaction


Nope it was 100% definitely exothermic! It said in the qu! Stop making people worry unnecessarily, if you don't know for definite, don't say.


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Reply 104
Original post by mrtum3000
Corrections:
''Tube B: calcium carbonate produced, solution goes cloudy'' - carbon dioxide makes limewater go cloudy
''How is methane obtained: Cows (?)'' - natural gas
''Element that has low boiling point: F'' - Rb is also valid I think


Could you say methane I obtained from crudeoil? also the SHC question, is it definitely 3444?
Reply 105
Original post by 1jonam16
so how many marks? 1 or 2? i calculated the energy released and then absorbed and got -1276 J, hence all along i wrote Joules and then converted at the end to KJ rather than using KJ all along (stupid misreading) thanks tho


i think youll only lose 1??
Original post by Fr3dg
are you dumb? it decomposes to carbonate ions and water and carbon dioxide, along with a metal ion if was bonded to that originally, for example calcium, since before being ionized, the hydrogencarbonate ion is usually ionically bonded to calcium, forming the salt, calcium hydrogen carbonate, get lost and stop making rubbish responses to people who are putting in effort to help other people


exactly, you're correct. he said it decomposes to calcoum ions. Secondly, i was taking the piss mate, chill out...
Reply 107
Original post by Sadxa
Could you say methane I obtained from crudeoil? also the SHC question, is it definitely 3444?


yeah probably since it is such a big focus of unit 1, and it is 3444, since 50*4.2*16.4 is 3444
Original post by Roquebrune2014
Nope it was 100% definitely exothermic! It said in the qu! Stop making people worry unnecessarily, if you don't know for definite, don't say.


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I agree, it was exothermic even because the bond energy change was negative
Original post by Fr3dg
i think youll only lose 1??

ok thanks, no need to be rude tho
SHC questions definitely is 3444!!
Original post by Sadxa
Could you say methane I obtained from crudeoil? also the SHC question, is it definitely 3444?
Original post by Wimsett
Which paper were you sitting? It seems like people got different results so maybe some people did triple and some did further additional


Further additional, what I didn't get anything in the thousands haha
Original post by theone97
I agree, it was exothermic even because the bond energy change was negative


Original post by Fr3dg
yeah probably since it is such a big focus of unit 1, and it is 3444, since 50*4.2*16.4 is 3444


could you say methane comes from fossil fuels? I was tempted to put natural gas, but aren't they synonymous?
Original post by Sadxa
Could you say methane I obtained from crudeoil? also the SHC question, is it definitely 3444?


Not sure I got crude oil.
Also 3444 is what I got.
Reply 114
Original post by BDunlop
The question was lowest, so it would have to be Rb


what?? it was lowest melting point, not lowest on the table, rubidium is solid at room temperature, flourine is a gas
Original post by milolj
Will you lose a mark for saying 1623 rather than -1623?


No they never take away a mark for not having the negative sign.
This is because it asks for the energy change rather than the net energy change if that makes sense.
Original post by RayRay99
Last question:

Low temp is needed for a higher yield of ammonia as the forward reaction is exothermic.
But this would decrease the rate of reaction too much so a comprise temp of 450'c is used.

A high pressure would also give a higher yield as there are fewer molecules in the right than on the left.
But a higher pressure costs too much money so a compromise pressure is used. (200atm)


I put this about how it is exothermic and so needs a lower temp, and then needs higher pressure to favour the side with fewer molecules
Reply 117
Original post by 1jonam16
could you say methane comes from fossil fuels? I was tempted to put natural gas, but aren't they synonymous?


im not sure specifically, if you sadi from fractional distillation of crude oil thatd be correct, perhaps its the same for natural gas, i said myself from the anaerobic decomposition of living matter by decomposers.
For the bond energy one I got -323 because I only went off the diagram and forgot to look at the equation and multiply each by the number of moles:frown: is there any chance I'll get a mark?
again i was thinking fractional distillation, wish i wrote it down. Are you simply amazing at chemistry? Haha you have the answers for everything.
Original post by Fr3dg
im not sure specifically, if you sadi from fractional distillation of crude oil thatd be correct, perhaps its the same for natural gas, i said myself from the anaerobic decomposition of living matter by decomposers.

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