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Chemistry: Post your doubts here!

L

leosco1995

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Amy Bloom said:
If u are at ease with working in grams then keep doing so. Try to work in moles from time to time, you never know. ^^
Click to expand...
I use both sometimes, but mainly grams. When I feel I am confident with working in moles, I use it. :p But yeah, I'll try to work in moles from now on.
 
hmlahori

hmlahori

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Oliveme said:
3 (a iii) the activation energy is high because it takes a lot of energy to break the Cl - Cl bond and that is why this reaction only takes place up in the atmosphere where it destroys the ozone layer.
3 (c) okay, this needs a lengthy explanation but overall, it's do to with the bong energy and the energy required to break them and then the graph goes down because the energy is released ---> exothermic. and then the graph stabilizes because products are formed and reaction has stopped.
4 (a iii) I'm not so good at organic chemistry sorry.
:) (y)
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Thanks but for question 3 part a iii its the I-I bond that breaks not the Cl-Cl bond.
 
hmlahori

hmlahori

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Amy Bloom said:
I guess question 4 a(iii) remained unanswered. so let me try to help you guys.
A bears optical isomerism because its central atom bears 4 different constituents.
D, on the other hand, has stereoisomerism, where there is one double bond and 2H groups on top and 2CH3 groups down or vice versa, or it can be One H bond and 1 CH3 bond on top and same at bottom.
See, A and D have 2 different types of isomerism: optical and stereo
However for B, has neither optical nor stereo for it has not 4 different constituents and no similar (e.g. 2H and 2 CH3) groups arranged in different ways.
Also C,E,F have isomers but not of different types, same for B.
Hope my answer has been helpful. ^^
Click to expand...

Well thanks i still have a little confusion i'll post it again maybe someone can explain differently but thanks anyways!
 
hmlahori

hmlahori

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http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_qp_21.pdf
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_ms_21.pdf
Q 3 (a iii) the answer is that activation energy is too high thats why reaction cannot take place. but the I-I bond is weaker than the Cl-Cl bond so it should be easier to break it and activation energy will be lower..........rite?
Q 3 (c) explain why the shape of the graph is like that shown in the mark scheme...........why does it have two humps?
 
angelicsuccubus

angelicsuccubus

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hmlahori said:
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_qp_21.pdf
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_ms_21.pdf
Q 3 (a iii) the answer is that activation energy is too high thats why reaction cannot take place. but the I-I bond is weaker than the Cl-Cl bond so it should be easier to break it and activation energy will be lower..........rite?
Q 3 (c) explain why the shape of the graph is like that shown in the mark scheme...........why does it have two humps?
Click to expand...

for 3a iii ) As you go down group 7, the number of electrons in the molecules increase which means the Van der Waal's forces between the diatomic molecules become stronger therefore the halogens become less reactive as you go down the group. (Because I-I bond is longer, it is weaker but that means it can be easily broken. It doesn't mean it will easily get attached to something else.)

3c) whenever an intermediate is formed, it has to be shown as a bump in an enthalpy/reaction diagram. Because it's like two reactions if an intermediate is involved..so technically its two enthalpy/reaction pathway diagrams in one.
 
hmlahori

hmlahori

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angelicsuccubus said:
for 3a iii ) As you go down group 7, the number of electrons in the molecules increase which means the Van der Waal's forces between the diatomic molecules become stronger therefore the halogens become less reactive as you go down the group. Where did you get I-I bond being weaker than Cl-Cl? I can't find that anywhere..

lemme see what's happenin in 3c.
Click to expand...

Since bond length of I-I is greater than Cl-Cl due to greater atomic radius the bond energy will be less also.......... rite?
 
hmlahori

hmlahori

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angelicsuccubus said:
for 3a iii ) As you go down group 7, the number of electrons in the molecules increase which means the Van der Waal's forces between the diatomic molecules become stronger therefore the halogens become less reactive as you go down the group. (Because I-I bond is longer, it is weaker but that means it can be easily broken. It doesn't mean it will easily get attached to something else.)

3c) whenever an intermediate is formed, it has to be shown as a bump in an enthalpy/reaction diagram. Because it's like two reactions if an intermediate is involved..so technically its two enthalpy/reaction pathway diagrams in one.
Click to expand...

rite that makes sense thanks!
 
angelicsuccubus

angelicsuccubus

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L

leosco1995

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angelicsuccubus said:
what are you confused about? Basically they are asking what are the products of a reaction between conc. sulfuric acid and sodium bromide, and the reaction between butanol and conc. sodium bromide.

2NaBr + 2H2SO4 -----> Na2SO4 + Br2 + 2H2O + SO2

and an alcohol can be dehydrated by a strong conc. acid into an alkene.
Click to expand...
Why can't NaBr react with the water? I made that mistake at first too. :s
 
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