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Chemistry: Post your doubts here!

knowitall10

knowitall10

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Hassi123 said:
http://www.novapapers.com/images/PDF/CIE/A-LEVEL/chemistry/2012jun/9701_s12_qp_43.pdf

Q3 part d. I thought benzene only reacts with br2 if its not aq or with a catalyst. Here there is an excess of br2 (aq) and it reacts with the benzene.
Please help?
Click to expand...
Assalamu Alaykum.
I think you've put the link of the wrong question. Because what you're asking of Q3 is different than what you're actually referring to on the paper.
Please make sure and ask.
If you're sure of it, then please do inform me because most probably i misunderstood the question or something.
 
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Hassi123

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knowitall10 said:
Assalamu Alaykum.
I think you've put the link of the wrong question. Because what you're asking of Q3 is different than what you're actually referring to on the paper.
Please make sure and ask.
If you're sure of it, then please do inform me because most probably i misunderstood the question or something.
Click to expand...
Oh I'm sorry, it's part e :p
 
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Hassi123

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knowitall10 said:
Assalamu Alaykum.
I think you've put the link of the wrong question. Because what you're asking of Q3 is different than what you're actually referring to on the paper.
Please make sure and ask.
If you're sure of it, then please do inform me because most probably i misunderstood the question or something.
Click to expand...
Can you help me with it? It's q3 part e*
 
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Asad

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iKhaled

iKhaled

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Ashique said:
knowitall10
could you help with q4 b iii- http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_4.pdf
Click to expand...
hey...
C40H82 -------> C16H34 + C24H48

a good way of explaining this question is to see how many bonds u have before the reaction and how many bonds u have after the reaction for example...

before the reaction we have 39 C-C bonds and 82 C-H bonds...after the reaction we have 15+22 = 37 C-C bonds and one C=C bond and 48+34 = 82 C-H bonds

so we have broken 39-37 = 2 C-C bonds and formed 1 C=C bond
bond broken = 2 x 350 = +700
bond formed = -610 = -610
enthalpy = + 90 kjmol^-1 !!

thats it..the mark scheme got the answer as +180 because he has used a different equation in cracking instead of forming C24H48 as our alkene he formed 2 moles of C12H24 and in that way we will have 2 C=C bonds instead of one and 4 C-C bonds instead of 2 because one mole of C12H24 contains 1 C=C bond and 10 C-C bonds so the 2 moles will contain 20 c-c bond and 2 C=C bonds 20+15= 35 so 39-35 = 4 C-C bonds so we had broken 4 C-C bonds and formed 2 C=C bond..in that way u will get 180 kj per mole instead of 90..both are correct though depending on the equation u made ;)

i hope u got it!!
 
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danyaljamil

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can anyone help with this if fe+3 and cl-1 are mixed will overall reaction be feasible and also of cr+2 and I2 here are the E(knot) values: fe+3 to fe+2 0.77 cl2 to cl-1 1.36 cr+3 to cr+2 1.82 I2 to I-1 0.54
mny thanks and sorry dont have marking scheme kinda home made question
 
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