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Chemistry: Post your doubts here!

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Ok
N how do we find if we have to add up all energies given in Born haber cycle or subtract them to find lattice energy ?
You should know what energies to use in the born-haber cycle. And to find lattice energy,
Latt energy change = Enthalpy change of formation - (the sum of rest of the energies you use in the cycle)
You will understand better if you try a past paper question on this.
 
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You should know what energies to use in the born-haber cycle. And to find lattice energy,
Latt energy change = Enthalpy change of formation - (the sum of rest of the energies you use in the cycle)
You will understand better if you try a past paper question on this.
Hmm
Is it not like lattice energy and the electron affinity= rest of energies on the left side?
 
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Hmm
Is it not like lattice energy and the electron affinity= rest of energies on the left side?
Nope ... don't get yourself confused like that with a particular formula. If you draw the Born-Haber cycle (I hope you know how to?) you will see what needs to be added and subtracted with the arrows ... and this cycle is just a more advanced version of Hess'law so you can can just take the different routes and well, you know, calculate whatever energy you want.

Thanks buddy tho i do edexcel not cie :)
If you can, find a question in edexcel and do ... or it wouldn't hurt to do this as well ... just practice so you can understand
 
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Nope ... don't get yourself confused like that with a particular formula. If you draw the Born-Haber cycle (I hope you know how to?) you will see what needs to be added and subtracted with the arrows ... and this cycle is just a more advanced version of Hess'law so you can can just take the different routes and well, you know, calculate whatever energy you want.


If you can, find a question in edexcel and do ... or it wouldn't hurt to do this as well ... just practice so you can understand
Yep thankfully i do know how to draw it xD
Yep i did one of the qs in my book ur way
It works
Thanks :)
 
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are they taking the ratio of the changes or sth? Coz Chlorine's oxdn state is decreasing by 2 and Sulphur's by 4 ...
so its B?
Yeah..I also got the same, then I thought they must have made it a ratio but then that's also no rule! so I was so confused, thought I wasn't calculating the oxidation states right, went back to the book, read again and again, read on the web, on chemguide then listened khanacademy...everything actually! but still....so this is it the question was wrong...I just found these topicals on the web but seems like they aren't authentic enough and questions can be wrong!
This is the actual MCQ from past papers :) Eugene99
View attachment 59161
Yeah...this is it! Thanks a lot!
I have a topical MCQs book for chemistry, "1000 chemistry MCQs with Help", but I found that questions set there contain syllabus from A2, which must be part of AS in old syllabus...any idea?
 
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Yeah..I also got the same, then I thought they must have made it a ratio but then that's also no rule! so I was so confused, thought I wasn't calculating the oxidation states right, went back to the book, read again and again, read on the web, on chemguide then listened khanacademy...everything actually! but still....so this is it the question was wrong...I just found these topicals on the web but seems like they aren't authentic enough and questions can be wrong!

Yeah...this is it! Thanks a lot!
I have a topical MCQs book for chemistry, "1000 chemistry MCQs with Help", but I found that questions set there contain syllabus from A2, which must be part of AS in old syllabus...any idea?
Yes, some topics in that book do contain question which relate to A2. However it is good for practice. Do this book for practice only, but focus more on the yearly ones.
 
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Use hess's law to calculate the standard enthalpy change of hydration of MgSO4
I know the method but answer is not correct
Can anyone explain it to me? :3
 
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http://maxpapers.com/wp-content/uploads/2012/11/9701_s13_qp_42.pdf

q:8a (iii)..why is that structure?
8c(i): how come there's no reduction in OH?
8a) (iii) By cross linking polymer chains it means, the link between the polymer chains which would be the same chains up and down............ so the cross link between them: HOCH2(CH2OH)C(CH2OH) CH2OH (thus the power 4 in the ms). The H at the top and bottom come because we r talking about it individually, when combined, the COO gets attached instead.
8c(i) They cause no reduction because they already have OH groups, because the cross linking itself has two OH's, plus, the question says that not every one available side chain is......

Hope it helps :D
 
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