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Wjec ch5 22 june 2016 thread

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Original post by wwwwwwwwwwwf
I got 860kJmol -1 for the born haber cycle for formation of BaCl2 and go -22.94 for the gibbs free energy change


Same but i think it was -860?
Original post by wwwwwwwwwwwf
I got 860kJmol -1 for the born haber cycle for formation of BaCl2 and go -22.94 for the gibbs free energy change


Excellent I got the same, though I wrote the Gibbs free energy as J instead of KJ, but it did start with a 2.
Original post by Formless
Same but i think it was -860?


Yeah i meant that my bad, formation is always exothermic so ya
Did anyone else get a negative value for emf of the two half cells Copper and Iron? And no reaction for the vanadium & iron?
Original post by Faisalshamallakh
Did anyone else get a negative value for emf of the two half cells Copper and Iron? And no reaction for the vanadium & iron?


the value was positive? i thought they do react
What was the positive electrode?
Reply 46
Avatar for ishanS
ishanS
5
i put Whatever the left hand electrode was! i think fe maybe?
Original post by Pixie1234
What was the positive electrode?
Original post by ALevel Student 1
No, I got 0.78V and I thought it was nickel not vanadium- cant remember seeing vanadium anywhere. But either way there was no reaction for that second one as it was a trick where it was Fe 2+ not Fe


Sorry my bad nickel! I had a positive value at first but I remembered that whatever half-cell is on the right hand side is the one being reduced. So I switched it over to right minus left to get a negative emf.
Original post by Faisalshamallakh
I had a positive value at first but I remembered that whatever half-cell is on the right hand side is the one being reduced.


Yeah it usually is, but wasn't in this case :/
Original post by wwwwwwwwwwwf
I got -860kJmol -1 for the born haber cycle for formation of BaCl2 and go -22.94 for the gibbs free energy change

Also got 59.5% copper content in the brass and 0.083 for NaOH concentration

Got 4.9x10-5 somewhere too I think, aswell as 7.0x105?


Got all of those same values apart from the Gibbs, forgot to convert the temperature :/
Original post by marethyu
-20 kJ ish



Yeah I'm almost certain its starch



k(h+)(CH3COOCH3)


Awwww crap :smile: i only put the H+ in :colonhash:
Original post by wwwwwwwwwwwf
Yeah i meant that my bad, formation is always exothermic so ya


Would you get the full 4 marks just for getting that value? Thought 4 marks was a lot just for that
Original post by sumeyyatontus
Would you get the full 4 marks just for getting that value? Thought 4 marks was a lot just for that


Hmm, i guess you had to remember the formula and get in correct for 1mark, use correct values for the formula (and remember to mulitply the energies for chlorine) for 1 mark.. uh then one for answer and another mark for correct sign/units
Original post by wwwwwwwwwwwf
Hmm, i guess you had to remember the formula and get in correct for 1mark, use correct values for the formula (and remember to mulitply the energies for chlorine) for 1 mark.. uh then one for answer and another mark for correct sign/units


How many marks would i lose in total if I had the rate equation as only with (H+)?
As my calculation after it also used the equation?
Original post by Firestartc
How many marks would i lose in total if I had the rate equation as only with (H+)?
As my calculation after it also used the equation?


I was talking about the born-haber cycle for BaCl2 in that post. Im not sure what question you mean:/
Original post by wwwwwwwwwwwf
I was talking about the born-haber cycle for BaCl2 in that post. Im not sure what question you mean:/


The first question, the one which should be rate = k(h+)(Ch3COCh3)
Original post by Firestartc
How many marks would i lose in total if I had the rate equation as only with (H+)?
As my calculation after it also used the equation?


I assume there will be error carried forward marks for the next part, so just 1 mark I think
What letters did everyone get for the 2 graphs? I got W and Y, not sure if the second one is right though
Original post by sumeyyatontus
What letters did everyone get for the 2 graphs? I got W and Y, not sure if the second one is right though


HCl at 0.1 mol which was W

and Ch3COOH (or w.e it was) at 0.001 which i think was Y but cant remember
I don't think I did very well in this. I think it was harder than last years and didn't help I messed up my timing.

For some reason I got stuck on simple questions like q3 where it was asking something about how the your answer to born haver cycle proves what the text is saying about hydrogen. I also got a different value for Gibbs!!

There was another confusing question but I can't remember it! Can someone make a unofficial mark scheme or list the questions with the amount of marks please!

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