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Aqa chem 4/ chem 5 june 2016 thread

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Original post by SirRaza97
Will this help?



yes thank you
Original post by chzm
http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN12.PDF

can someone please explain 2(b) to 2(d) for me please

I dont understand how Gibbs free energy change is represented on a graph


2(b) The straight line equation y = mx + c can be used to represent the the gibbs free energy equation where y = ΔG, m = -ΔS x = T and c = ΔH. To calculate the gradient you just do the change in y divided by the change in x. So take two points on the line and find the corresponding y an x values and do the same for a second point and do this calculation:

y1 - y2 / x1 - x2

The slope is -ΔS so the units are J K-1 Mol-1

2(d) is understanding that the rate of change of entropy changes for an element in it's different states. If the rate of change of entropy has changed then the slope (gradient) of your line has changed. So the ammonia has turned to liquid as the temperature is going lower.
(edited 7 years ago)
Do we need to know all the reactions of the different cells in the nelson thornes book in the redox equilibria chapter?
If I said 'reactants' instead of 'reagents' would I lose a mark??
Original post by sarahreads
Do we need to know all the reactions of the different cells in the nelson thornes book in the redox equilibria chapter?


Only the hudrogen fuel cell
Original post by lahigueraxxx
If I said 'reactants' instead of 'reagents' would I lose a mark??


No, they are synonymous.

What context are you talking about?
Original post by Cadherin
No, they are synonymous.

What context are you talking about?


http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-QP-JUN11.PDF

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-MS-JUN11.PDF

5fi and 5fiii (thank you btw :smile: )
Original post by lahigueraxxx


No problem :smile:

Unless the examiner is a Vietnamese child marking your paper (which I wouldn't put past AQA), they will accept both 'reagents' and 'reactants' as synonymous.

Besides, my chem teacher (and I think many others) refer to 'reagents' and not 'reactants'.
Original post by Cadherin
No problem :smile:

Unless the examiner is a Vietnamese child marking your paper (which I wouldn't put past AQA), they will accept both 'reagents' and 'reactants' as synonymous.

Besides, my chem teacher (and I think many others) refer to 'reagents' and not 'reactants'.


Haha okay cool - thanks! x
Just found this good quizzlet for Transition Metal Colours https://quizlet.com/_2dfodx
(CuCl4)2-
i know this is a green yellow solution
do they accept just green solution?
For definition questions, which will surely come up in the exam- instead of learning the super long definitions, can we just write the equation. Eg Define enthalpy of dissociation. Answer: AB(s)-----> A+(g) + B- (g).

Any cases where they don't allow this? -just saves time memorising definittions
Original post by Lilly1234567890
(CuCl4)2-
i know this is a green yellow solution
do they accept just green solution?


yeah, but best bet is to write yellow-green
DO we need to know the hydrogen fuel cell equations in alkaline conditions? or just acidic?
Original post by Signorina
DO we need to know the hydrogen fuel cell equations in alkaline conditions? or just acidic?


both.
Original post by Lilly1234567890
(CuCl4)2-
i know this is a green yellow solution
do they accept just green solution?


Markschemes have green/yellow solution. However, / means you can say either green OR yellow and still get the mark for either one. I state green/yellow solution to stay on the safe side, but you'd be fine.

Original post by OloMed
For definition questions, which will surely come up in the exam- instead of learning the super long definitions, can we just write the equation. Eg Define enthalpy of dissociation. Answer: AB(s)-----> A+(g) + B- (g).

Any cases where they don't allow this? -just saves time memorising definittions


That's fine, however you MUST state for any definition when using equation:

The enthalpy change for (equation with state symbols)

E.g define enthalpy of solution:

The enthalpy change for
AB(s) + aq -> A(aq) + B(aq)
Original post by Suits101
Markschemes have green/yellow solution. However, / means you can say either green OR yellow and still get the mark for either one. I state green/yellow solution to stay on the safe side, but you'd be fine.



That's fine, however you MUST state for any definition when using equation:

The enthalpy change for (equation with state symbols)

E.g define enthalpy of solution:

The enthalpy change for
AB(s) + aq -> A(aq) + B(aq)


Super. Thanks. Don't see why people bother writing out long definitions!
Original post by Signorina
DO we need to know the hydrogen fuel cell equations in alkaline conditions? or just acidic?


Strictly speaking, you don't need to know them.

In the exam they will tell you which equations to use, such as 'write the half equation at the hydrogen electrode in a hydrogen-oxygen fuel cell in acidic/alkaline conditions' or if they don't then you can use either one.

I say you don't need to learn them because you need to know what happens at the electrodes, e.g you know hydrogen is a reactant so you can deduce how to get to hydroxide ions (if alkaline) or hydrogen ions (if acidic) and you know oxygen is a reactant so you can deduce how to get to hydroxide ions (if alkaline) or hydrogen ions (if acidic) once again.
Some help with oxidising and reducing agents?
The strongest reducing agent has the most negative electrode potential and the weakest reducing agent has the most positive electrode potential
The strongest oxidising agent has the most positive electrode potential and the weakest oxidising agent has the most negative electrode potential.
Is that correct?
So in this table ImageUploadedByStudent Room1466277155.356368.jpg

The STRONGEST R.A would be H2O2 and the WEAKEST R.A would be H2O

The STRONGEST O.A would be H2O2
and the WEAKEST R.A would be O2

???


Posted from TSR Mobile
Does anyone know why with [Co(H2O)6]2+ NH3 is able to fully displaced (by ligand substitution) all the H2O molecules however with [Cu(H2O)6]2+ only 4 H2O molecules will be displaced by NH3?

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