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Chemistry: Post your doubts here!

h4rriet

h4rriet

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Alice123 said:
cud u please quote values of bonds broken and formed...
Click to expand...
No, forget about the bonds broken - bonds formed; you can't do it that way. Only ONE compound is made, so all the bonds made are its own, and all the energy of the reaction goes to it and it alone. There are 2 moles of it, so the energy it used to make 2 compounds. To find the energy needed to make 1 mole, divide the energy needed to make 2 moles by 2. (It's given in the question). Now you have the energy needed to make 1 compound. You need to get the energy needed to break the bonds in that 1 compound. The number of bonds in the compound is 3, so you divide the energy by 3.
 
J

Jinkglex

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Alice123 said:
cud u please quote values of bonds broken and formed...
Click to expand...

i believe the answer is A, first of all you see that 500K will give more K.E to the molecules, so D is out. Then since fraction of molecules cant be more then original, B is out. Finally, according to Boltzmann distribution laws the curve will become shorter and have a less sharp peak, so C is out, because the peaks are equal in C which isn't possible. :)
 
L

LeoMessi

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HubbaBubba said:
More help please! :coffee:
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23 C because only Pentan-3-ol has a chiral carbon. Drawing the displayed formula for such type of questions REALLY helps
30 Na will react with an alcohol to give R-O Na , the number of oxygens remains the same. Elimination will occur with Al2O3, with option B esterification will occur with the acid which increases the number of oxygen atoms and in option C OH group will be replaced by HBr. So D is the answer
 
h4rriet

h4rriet

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Raiyan3 said:
Yet again im posting please do help
" Question number 7 please help
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
And question number 11 and 23
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_12.pdf "
Click to expand...
What you have to do is draw ICE charts for all the equations (A, B, C and D). Then see if the sum of equilibrium moles is 2+x/2.
Here's the ICE chart for D:
s4J2eot.jpg
 
HubbaBubba

HubbaBubba

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LeoMessi said:
23 C because only Pentan-3-ol has a chiral carbon. Drawing the displayed formula for such type of questions REALLY helps
30 Na will react with an alcohol to give R-O Na , the number of oxygens remains the same. Elimination will occur with Al2O3, with option B esterification will occur with the acid which increases the number of oxygen atoms and in option C OH group will be replaced by HBr. So D is the answer
Click to expand...
I wrote Na for 30, but the answer is CH3COOH. I have no idea why, as that would give an ester, and that has two O atoms.
 
h4rriet

h4rriet

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h4rriet

h4rriet

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HubbaBubba said:
More help please! :coffee:
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24. Because of the rings, the compound can't be planar. Because of the rings, there can exist no cis-trains isomers.
8. Pressure depends on the mole ratio, so you'll need to be calculating the moles here. Mass of H2=2 g, molecular mass=2, so n=1. Calculate the total moles in A, B, C and D. C's the answer, if I'm not mistaken.
11. Draw an ICE (initial moles, change in moles, equilibrium moles) chart.
 
Raiyan3

Raiyan3

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h4rriet said:
What you have to do is draw ICE charts for all the equations (A, B, C and D). Then see if the sum of equilibrium moles is 2+x/2.
Here's the ICE chart for D:
s4J2eot.jpg
Click to expand...

Rightttt Thanks alot buddy! That really did help buddyy!
 
HubbaBubba

HubbaBubba

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h4rriet said:
24. Because of the rings, the compound can't be planar. Because of the rings, there can exist no cis-trains isomers.
8. Pressure depends on the mole ratio, so you'll need to be calculating the moles here. Mass of H2=2 g, molecular mass=2, so n=1. Calculate the total moles in A, B, C and D. C's the answer, if I'm not mistaken.
11. Draw an ICE (initial moles, change in moles, equilibrium moles) chart.
Click to expand...

I did draw an ICE, but I don't understand how they got 4(b-x) at the bottom. I just got (b-x)^2
 
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