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How was Chem 4 and Chem 5?? (edexcel) watch

1. didnt anyone do, nuffield chemistry?
2. its definitely no units, u got O multiplied by N2 divided by NO2 squared which gives say Pascals squared divided by Pascals squared i.e. no units
3. (Original post by Hoofbeat)
What did anyone get for the Kp question in U4? Some people at my school got 2450 like few people on here said, but the rest of us (inc silly sally on here) got 9800atm (Soz, sally but it def has units). I got 9800 and don't see what I did wrong? What did you guys get?

Overall U4 was reasonable, but U5 horrible!
i got 2450.....
NO O2 N2
intial moles 1 0 0
equillibirum moles 1-.99=.01 .99/2=.495 .495

total moles = 0.1+0.495+0.495 = 1

partial pressures : NO= 0.01/1 x 1.5 = 0.015

02and N2 = .495/1 x 1.5 = 0.7425

Kp = (.7425)(.7425) / ((0.015)square) =2450.25
4. (Original post by [_Z_])
i got 2450.....
NO O2 N2
intial moles 1 0 0
equillibirum moles 1-.99=.01 .99/2=.495 .495

total moles = 0.-1+0.495+0.495 = 1
partial pressures : NO= 0.01/1 x 1.5 = 0.015
02and N2 = .495/1 x 1.5 = 0.7425
Kp = (.7425)(.7425) / ((0.015)square) =2450.25
It was actually 2NO in the original equation - doesn't that make a difference
5. yeah u get the No Partial pressure squared

basically it was 0.7425 squared divided by 0.015 squared which gives the correct answer
6. (Original post by Silly Sally)
It was actually 2NO in the original equation - doesn't that make a difference
yes it does... and thats why i have squared the partial pressure of no which is 0.015. to give the answer.....i havent written the equation....
7. (Original post by [_Z_])
yes it does... and thats why i have squared the partial pressure of no which is 0.015. to give the answer.....i havent written the equation....
DAMN! So i didnt see the 2 in the original formula, which is where I went wrong. grrrrrrr
8. Does n e one remember what they got for the value of k for the rate question? For the first bit i got something like 0.8

oh yea and the reaction with respect to water was 0 order rite?
9. yup it was 2450.25

and yes the rate eqn depends on how u read the grpah it shud have been between 0.8 and 0.9 i think

me got 0.8333 so i aint complaining... although i have a funny feelin i rote
0.08333 it would b sooo typical of me to do just that
10. (Original post by Dust)
yup and thats rite as well.. i checked it after the exam...
yeah
11. (Original post by Dust)
yup it was 2450.25

and yes the rate eqn depends on how u read the grpah it shud have been between 0.8 and 0.9 i think

me got 0.8333 so i aint complaining... although i have a funny feelin i rote
0.08333 it would b sooo typical of me to do just that
No you dont need to read from graph, though i think you wont lose mark for this.

For first order reaction, half-life = ln2 / k

then you can find k easily and then you have to convert its unit to s-1
12. (Original post by DaKe)
Does n e one remember what they got for the value of k for the rate question? For the first bit i got something like 0.8

oh yea and the reaction with respect to water was 0 order rite?
It may not be 0 order
remember that water has a constant density and so its "concentration" is constant no matter how much is used.
so although it is in excess, it is also possible that the order wrt water is not zero
13. (Original post by scarlet ibis)
phew, u5 was hard! i drew a reflux/condening colum coming out of one of those quickfit flasks, with an inlet for chlorine, being heated from below (Not in a water bath tho, cos it was at 110 C) and with a source of UV light.

what did everyone else get for that rates question?
As we are not asked to draw the preparation of chlorine, I think chlorine is not added usually. It may be generated by some other reagents.

I didnt draw the source of UV light as the sunlight just provides this. It is not an apparatus!

There should be one mark award for inlet of methylbenzene, not sure though
14. God i feel like im in heaven.

I thought i was the only one who found unit 5 a *****. Unit 4 was good but i'm still kickin myself over minor mistake that cost me loadsa marks.

Can anyone find out OFFICIALLY whether edexcel are gonna put the boudaries down. Im so chuffed.

Peace all
15. How to follow the progress of the reaction in the kinetics question?
16. (Original post by keisiuho)
How to follow the progress of the reaction in the kinetics question?
I said use titration - if more carboxylic acid produced, the larger the vilume of the alkali required for neutralisation!!! Probably wrong like most of the paper!!!
17. By the way did anyone get 4/3 for the rate of constant proportionality? Cos everyone seems to have got between 0.8-0.9 The chem unit 5 has rally made me depressed!!!!
18. (Original post by keisiuho)
As we are not asked to draw the preparation of chlorine, I think chlorine is not added usually. It may be generated by some other reagents.

I didnt draw the source of UV light as the sunlight just provides this. It is not an apparatus!

There should be one mark award for inlet of methylbenzene, not sure though
i'm sure it said in the question: chloromethylbenzene is produced by passing chlorine gas through boiling methylbenzene, so you'd have to have a tube to let the chlorine in!
19. (Original post by Silly Sally)
I said use titration - if more carboxylic acid produced, the larger the vilume of the alkali required for neutralisation!!! Probably wrong like most of the paper!!!
thats what i said too.
20. I agree with the last two points.

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