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AQA CHEM2 ~ May 23rd 2012 ~ AS Chemistry

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Ahh, just missed that xD Thank you but that is a very misleading question...

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Reply 1881

Ursin

[INDENT]

Original post by Ursin

CH3CHCH2Br I think, you have to form the most stable carbocation, i.e. the carbon with the positive charge is the one with the most carbons leading into it.

Replace Br with H, my bad.

Reply 1882

Dirtybit

Can somebody pleasseeee explain to me how to do q2c http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM2-W-QP-JAN10.PDF

Im clueless!

Reply 1883

JesusIsMyHomeboy

Oh God.. i'm bricking it. There is a special place in hell for extraction of metals. Good luck to all!

Reply 1884

Millyshyn

Does anyone have the exact mark scheme definition for Le Chatelier's principle? I can never phase it very well and don't seem to be able to find a paper it was on at the moment..

Reply 1885

Mocking_bird

Original post by Tullia

2-bromopropane.

That isn't the intermediate though, thats the actual major product. :cool:

Reply 1886

Millyshyn

Original post by Spellstheend

Really want this exam over with now, kind of wish it was in the morning as I don't know what to do between now and the exam

That's exactly how I feel. I don't feel like I can do any more revision between now and the exam because none of it is going in anyway :/ So I'm just wasting time when I could be revising for other exam if it was in the morning.

Reply 1887

Seanyboy57

Original post by Dirtybit

Can somebody pleasseeee explain to me how to do q2c http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM2-W-QP-JAN10.PDF

Im clueless!

You've been given the values for the enthalpy changes of the reaction. All you need to do is label the right arrows on the cycle they've given you with the enthalpy changes, and then use Hess's Law to calculate the unknown enthalpy like you would any other question. :smile:

Reply 1888

starfish232

Original post by StudentAnon

Isn't a carbocation an ion where a carbon has a positive charge?

"Two products are formed when propene reacts with hydrogen bromide. Draw the structure of the intermediate that leads to the formation of the major product ..."

What would that be? :smile:

The major product would be formed with the free carbon furthest from the end of the chain (if that makes any sense). You'd draw a +ve charge on that carbon and that would be the intermediate for the major product as it's the most stable.

So in this case, the intermediate is that the positive sign is on the second carbon as it's a secondary carbocation. I've attached it for you.

(edited 11 years ago)

Carbocation.png2.7KB

Reply 1889

JenniS

Original post by Spellstheend

Really want this exam over with now, kind of wish it was in the morning as I don't know what to do between now and the exam

same, feel like I'm wasting time when I have soo many other exams to revise for!

Reply 1890

Dineen94

Original post by Dirtybit

Can somebody pleasseeee explain to me how to do q2c http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM2-W-QP-JAN10.PDF

Im clueless!

If you use Hess' Law (the enthalpy change is independent to the route take and is dependent only on the initial and final states) the arrows can be reversed in direction to follow a different route from the reactant to the product. Note that reversing the arrows will also reverse the Delta H value. I.e. +4kjMol-1 will become -4kjMol-1

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good luck guys!!

Original post by Millyshyn

Does anyone have the exact mark scheme definition for Le Chatelier's principle? I can never phase it very well and don't seem to be able to find a paper it was on at the moment..

When a system at equlibrium is disturbed, the equilibrium shifts in the direction that tends to reduce the distrubance.

See the January 2011 paper, question 1(c)(i) :smile:

Reply 1893

Mocking_bird

Bit confused with nucleophillic substitution and ammonia.
One things saying you have to add :NH4 on the end of the mechanism, anothers saying :NH3 and something else is saying nothing at all.

Anyone got a good diagram of their mechanism?

Reply 1894

Dineen94

Does anybody know what catalysts we have to learn for all the reactions?

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Reply 1895

starfish232

Original post by JesusIsMyHomeboy

Oh God.. i'm bricking it. There is a special place in hell for extraction of metals. Good luck to all!

Completely agree with you! Too many equations for a topic I really could care less about.

Reply 1896

Spellstheend

Original post by Dirtybit

Can somebody pleasseeee explain to me how to do q2c http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM2-W-QP-JAN10.PDF

Im clueless!

To go from H+ (g) + Cl- (g) they have gone via H (g) and Cl (g)

So to get H (g) and Cl (g) from the original equation its -963 (using the equation in the table and reversing the sign)

Then the next part is easier, to go from the H (g) and Cl (g) you have just formed, it goes to HCL, this is -463 (straight from the table)
Then from HCL to your final product is again the figure straight from the table, -75

add all these together,

-963 + -463 + -75 is your answer

Reply 1897

Spellstheend

Original post by Millyshyn

Original post by JenniS

same, feel like I'm wasting time when I have soo many other exams to revise for!

Yep that's exactly it, I have 2 more exams tomorrow, both of which I need to revise for as a matter or urgency :P But I cannot revise for that now when chemistry is a couple of hours away -_-
And I won't get back till 5pm as I live far away from college.
Also I tend to feel more anxious when its the afternoon, I've had all morning to build up stress :P Whereas the morning I get up so early to make it in ontime that I have no time to think and just do it
Oh well can't do anything about it :')