[undertaker1]

(Original post by Doctor.)
1) Not seen you in AGES lol

2) I think it's in this thread somewhere, can't find the pdf on my laptop :/ It's a mess

Hows revision going?!

i'm going to start my learning from scratch today. i aint done it since last year. i've forgotton most of my organic chemistry lol.

btw how have you been keeping???

[Doctor.]

(Original post by Sheo)
Hello guys,

Just trying to do this Chem 4 question and I can't seem to get the answer for the concentration of Q in exp. 4

The answer for initial rate of reaction for experiment 3 is 8.1x10-5 and the answer for exp. 4 is 6.7x10-5

I seriously cannot remember how I did this last time so any help would be appreciated!


Attachment 151336

The way I did it was,

You see the first experiment - You can use that to find the value of 'K'. once done, now you can simply slot values for each experiment as there is always 1 missing! The value of K is remaining constant

(Original post by jamiepango)
Ah okay. I worked it out using the rate constant, but you can do answer it without finding k as well.

If you use the first and 4th steps, you can write rate equations in terms of k. If you rearrange both equations so that K is the subject, you can equate the 2 equations. Then you should be left with [Q]^2, which you can find because you have the values for everything else.

Let me know if you get the answer

It's pretty important that you do find the value of K...Can't remember but I'm sure you get penalised if you just work it out without K. Was in a past paper, but then again it may have actually stated you need to find the value of k, then work out the values
but yeah, safe to do it rather than lose marks!

[Doctor.]

(Original post by undertaker1)
i'm going to start my learning from scratch today. i aint done it since last year. i've forgotton most of my organic chemistry lol.

btw how have you been keeping???

Dude hurry up and learn!!! I need someone to test me PS make sure you know how to name the N-substituted amides, they're absolute hell

I've been VERY bored The time from January to now has sort of flown by

Did my first exam 2 days ago These exams are dragging so much

[ThumbsUp]

chem4 is hard but using a-levelchemistry.org.uk is so helpful!

[Doctor.]

By the way guys, I finished amines chapter a little bit a go. Got amino acids...which is like under a page to do and Polymerisation .

After Polymerisation, I think I will call it quits, going to get a move on to maths! Then tomorrow get NMR sorted I think Hopefully I can get that sorted ASAP so I can make a start on papers and crap load of questions

[Doctor.]

(Original post by ThumbsUp)
chem4 is hard but using a-levelchemistry.org.uk is so helpful!

Being honest, I don't find it that helpful. some of the revision notes are pretty much too detailed. I found the notes are really 'not made to the mark scheme' - It's great for understanding EVERYTHING but go too far in some topics!

Nelson Thorns isn't bad, and Collins book I love it lol

[undertaker1]

(Original post by Doctor.)
Dude hurry up and learn!!! I need someone to test me PS make sure you know how to name the N-substituted amides, they're absolute hell

I've been VERY bored The time from January to now has sort of flown by

Did my first exam 2 days ago These exams are dragging so much

lol, i need to dig my notes out and get back into chem revision again. its too hotttt to revise lol.
im planning on finishing kinetics, equlibria and acid/bases by wednesday. finish the organic by next sunday. this is my third attempt so i'm going to run through it all lol.

make sure you do all the past papers from 2002 onwards. i was alot more motivated for my jan exams compared to june cuz i've got my aston pharmacy offer but as i had paid for my resits i thought i might aswell do them.

[masterhr1]

If temperature can change Kc, why can't pressure? They both shift equilibrium...

[jamiepango]

(Original post by Doctor.)
The way I did it was,

You see the first experiment - You can use that to find the value of 'K'. once done, now you can simply slot values for each experiment as there is always 1 missing! The value of K is remaining constant


It's pretty important that you do find the value of K...Can't remember but I'm sure you get penalised if you just work it out without K. Was in a past paper, but then again it may have actually stated you need to find the value of k, then work out the values
but yeah, safe to do it rather than lose marks!

Yes I did it your way as well, but the poster said finding K was the next question so I just used another way without having to find K. Either way works :

[ThumbsUp]

(Original post by Doctor.)
Being honest, I don't find it that helpful. some of the revision notes are pretty much too detailed. I found the notes are really 'not made to the mark scheme' - It's great for understanding EVERYTHING but go too far in some topics!

Nelson Thorns isn't bad, and Collins book I love it lol

lol well its basically the only other resource i have apart from my book and past papers. I honestly havent checked out the whole site (probably why I dont get As in chem :P) but the list of equations given is a life saver!

[Doctor.]

(Original post by ThumbsUp)
lol well its basically the only other resource i have apart from my book and past papers. I honestly havent checked out the whole site (probably why I dont get As in chem :P) but the list of equations given is a life saver!

so true, the list of equations is awesome

(Original post by masterhr1)
If temperature can change Kc, why can't pressure? They both shift equilibrium...

What if you have the same number of moles on both sides?

(Original post by undertaker1)
lol, i need to dig my notes out and get back into chem revision again. its too hotttt to revise lol.
im planning on finishing kinetics, equlibria and acid/bases by wednesday. finish the organic by next sunday. this is my third attempt so i'm going to run through it all lol.

make sure you do all the past papers from 2002 onwards. i was alot more motivated for my jan exams compared to june cuz i've got my aston pharmacy offer but as i had paid for my resits i thought i might aswell do them.

I know what you mean, its boiling!!! Which is strange,Manchester is usually very VERY dull, gray and always rainy

[Sheo]

(Original post by undertaker1)
right people 2.5 weeks left till this exam!!!

anyone have the jan 12 paper?

Here you go

[Sheo]

(Original post by Doctor.)
.

(Original post by jamiepango)
.

Thanks guys!
I don't know why I've never used K and just rearranged to find my answers but gone down the complicated route with so many steps I think I may have lost at least one mark in the Jan 12 paper with the first question.

Using K is so much easier! I managed to get the answer, which was 6.7x10^-4

(Original post by MuffinMonster)
Is the answer 6.0x10-3?
Compared to the first one, the rate of 4 is 1/6 of the rate.
But P is 1.5 times bigger
So if exp 1 has a conc of 1.8 for P, it's rate would be 2.7.
2.7/0.3 would be 9.
Square root 9 (second order) is 3.
So the conc of Q in exp4 is 3 times the one in exp 1.

the answer is 6.7x10^-4

I just worked out the rate constant using experiment 1 which is 3750 then rearranged the rate equation to get Q^2 as the subject and then worked out a value. I then square rooted this to get just Q. Sorry I hope that makes sense.

[Doctor.]

(Original post by Sheo)
Thanks guys!
I don't know why I've never used K and just rearranged to find my answers but gone down the complicated route with so many steps I think I may have lost at least one mark in the Jan 12 paper with the first question.

Just one mark overall? That's awesome!!

[jamiepango]

(Original post by Sheo)
Thanks guys!
I don't know why I've never used K and just rearranged to find my answers but gone down the complicated route with so many steps I think I may have lost at least one mark in the Jan 12 paper with the first question.

Using K is so much easier! I managed to get the answer, which was 6.7x10^-4

No problem, glad I could help. The more practice you do, the less likely you'll make mistakes in the real thing

Going to start learning the organic synthesis stuff now, there's so much to remember...

[Doctor.]

(Original post by jamiepango)
No problem, glad I could help. The more practice you do, the less likely you'll make mistakes in the real thing

Going to start learning the organic synthesis stuff now, there's so much to remember...

Just finished Polymers! Will be moving on to a very brief look at Organic Synthesis, don't see much point in learning it since ill forget it in a few days Then Is NMR I how that chapter :/

How are you finding it all?

[jamiepango]

(Original post by Doctor.)
Just finished Polymers! Will be moving on to a very brief look at Organic Synthesis, don't see much point in learning it since ill forget it in a few days Then Is NMR I how that chapter :/

How are you finding it all?

Organic synthesis and structure determination are my 2 worst chapters in this unit. I've made a map of all the mechanisms/reagents/conditions so hopefully I can just memorise that

If you forget it easily, perhaps learn a bit a day instead of all at once? So maybe you could do 2 reactions a day from now, which should just about cover you to the exam?

Oh and I need to memorise the table of complexes with all the colours for chem5 as well

[Sheo]

(Original post by Doctor.)
Just one mark overall? That's awesome!!

nonono, I'm resitting the exam, I meant lost one mark in the first question in my original paper from Jan which I believe was a rate equation type question.

do you really think I'd be crazy enough to resit it just for one mark? haha this unit is HUGE to start with and that exam in particular was a nightmare!

How are you feeling about the exam? I'm sure I've seen you on a previous thread in January about chemistry

[Doctor.]

(Original post by Sheo)
nonono, I'm resitting the exam, I meant lost one mark in the first question in my original paper from Jan which I believe was a rate equation type question.

do you really think I'd be crazy enough to resit it just for one mark? haha this unit is HUGE to start with and that exam in particular was a nightmare!

How are you feeling about the exam? I'm sure I've seen you on a previous thread in January about chemistry

Ah right I see, I was a little confused

I don't feel confident enough to say I am great at it all. Although I think I am getting better, like I have gone through most of the work but not started any past paper questions Hopefully I will be done with revision tomorrow. Then going to go past paper question crazy. I have packs from 2000-2012 for each section going to be a pain in the arse getting them all done

In January, I did CHEM1, CHEM2 and CHEM5. Only doing this CHEM4 just to ensure I have my A overall lol (I failed the ISAs )

[undertaker1]

(Original post by Sheo)
Here you go

thank you