AQA Chemistry C3 - Unofficial Mark Scheme

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.

For the energy change I divided 3444 by 0.8 and go 4305? ANYONE ELSE?

I am not sure about the bond energy questions, some are saying -1623 and some -1276, which is the right answer? Could someone please say why the other one is wrong also.

what?? it was lowest melting point, not lowest on the table, rubidium is solid at room temperature, flourine is a gas

I got that as well

Thought on grade boundaries for both C2 and 3?
I think C2 - 51, C3 - 44?

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

For the last question I didn't refer to equilibrium would I still get the marks?

I said:
A low temperature increases the yield but slows down the rate of reaction
A high temperature would lower the yield
A low pressure increases the yield but is very costly to maintain and dangerous.

For an A or A*


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For the last question I didn't refer to equilibrium would I still get the marks?

I said:
A low temperature increases the yield but slows down the rate of reaction
A high temperature would lower the yield
A low pressure increases the yield but is very costly to maintain and dangerous.

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

This is what I got, hopefully this is right! That question was long for only 3 marks

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)