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OCR Chemistry F322~ 4th June 2013~ AS Chemistry

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Original post by Hardworker?
Some help please,
do we need to know specific polymers and their uses, if so which ones?


Just Choloroethne to make PVC
AND
Tetrafluoroethene to make PTFE
Reply 1881
Avatar for iamvick
iamvick
2
Original post by TheFootyKing19
Ooooops yeah! Mis read functional group somewhere!

Define Hess's Law


Hess's Law states that if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
Reply 1882
Avatar for Ché.
Ché.
Original post by Hardworker?
Some help please,
do we need to know specific polymers and their uses, if so which ones?


Not necessarily, I am sure...
They'll be put in light context - Chemistry normally is examined very specific to the specification...
That's awesome for us!



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Original post by F95
ohh okay thankyou!! is that the case for all questions like this? or just for this particular q?


All questions like this, although they're usually nice and give whole numbers, but decimals do trip people up so watch out :smile:
Original post by Chemistry95
I'm doing this as a resit, and im just saying if anybody does do badly once you do A2 then you come back to this it's so much easier so if you do bad this year just resit it next june and you'll most likely do so much better :biggrin:


Why is A2 harder? What is harder about it? I'm debating about whether to drop chemistry or not. I don't need it for uni as I wanna do maths.
Reply 1885
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SAS18
10
Original post by needtosucceed=)
I hope that makes sense :smile:

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Original post by elliebennett
Hey,
basically you have to kind of form an algebraic equation.

So you know the overall enthalpy change = -184
and you H-H bond = 463
and Cl-Cl bond = 246
but you wanna find out 2HCl
soo.. H-H + Cl-Cl --> 2HCl = -184

463 + 246 --> 2HCl = -184
463 + 246 = 679,
so you have work out what you would have take from 679 to make the overall enthalpy change = -184, (basically work out the difference)
so 679 - 863 = -184, so you know that 2HCl must = 863

however the question asks for just HCl, so you just divide 2HCl = 863/2 = 431.5! :smile:


Thank you guys soooo much!!!
Original post by iamvick
Hess's Law states that if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.


Top!

State environmental concerns over:
HCl (1)
CO (2)
NO (2)

State the uses of methanol (2)
Reply 1887
Avatar for WaseemB
WaseemB
...
(edited 10 years ago)
Original post by GeneralOJB
Why is A2 harder? What is harder about it? I'm debating about whether to drop chemistry or not. I don't need it for uni as I wanna do maths.


a2 is a progression from AS, therefore naturally its harder..the concepts arent as straight forward as they are at AS and the exams can trip you up. its interesting though
Reply 1889
Avatar for SAS18
SAS18
10
Also about question 5 b on jan 2012 is there a typo?? or just me?
Original post by TheFootyKing19
Top!

State environmental concerns over:
HCl (1)
CO (2)
NO (2)

State the uses of methanol (2)


Can produce acid rain, or react with buildings
Is toxic and reduces the amount of oxygen going in your body
Low level ozone, photochemical smog

Petrol additive
For Feedstock

:biggrin:


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Original post by TheFootyKing19
Top!

State environmental concerns over:
HCl (1)
CO (2)
NO (2)

State the uses of methanol (2)


sorry im just gonna butt in..

- corrosive and toxic
- toxic, reduces the ability of the blood to carry oxygen
- forms photochemical smog and low level ozone
- petrol additive, making esters, methylated spirits (i think?)


define average bond enthalpy (2)
why would the value for enthalpy change be different when using average bond enthalpy 1)
why is international cooperation important (3)
what are the definitions guaranteed to get maximum marks for:
Enthalpy change of reaction/ formation and combustion?
If anyone can be bothered, try these:

Define average bond Enthalpy (2)
Define standard Enthalpy change of reaction (2)
State standard conditions (1)
State the test and colour change for Alkane and Alkene (3)
How can you make Butylpentanoate, state the conditions and give an equation (5)
How does an increase in concentration increase the rate of reaction? (2)
State two features of E/Z isomerism? (2)
Original post by SAS18
Also about question 5 b on jan 2012 is there a typo?? or just me?


what word? seems fine to me
Original post by TheFootyKing19
If anyone can be bothered, try these:

Define average bond Enthalpy (2)
Define standard Enthalpy change of reaction (2)
State standard conditions (1)
State the test and colour change for Alkane and Alkene (3)
How can you make Butylpentanoate, state the conditions and give an equation (5)
How does an increase in concentration increase the rate of reaction? (2)
State two features of E/Z isomerism? (2)


the average enthalpy change when one mole of gaseous covalent bonds are broken
the enthalpy change that occurs in the molar quantities expressed in a chemical equation under standard conditions
298k and 1atm
alkene - br2 would decolourise it, alkane - it would stay brown
butan-1-ol + pentanoic acid. conc h2so4 + reflux. cba to write the equation lol
more particles per unit volume therefore more successful/frequent collisions
c=c, restricted rotation and each carbon bonded to 2 different atoms/groups of atoms
Reply 1896
Avatar for SAS18
SAS18
10
Original post by needtosucceed=)
what word? seems fine to me


could you tell me how to do it please?
Original post by SAS18
could you tell me how to do it please?


use the equation actual/theoretical x100

ignore the tonnes, just use grams

work out the moles of each one then divide one by the other.
Reply 1898
Avatar for JimmyA*
JimmyA*
5
Original post by GeneralOJB
Why is A2 harder? What is harder about it? I'm debating about whether to drop chemistry or not. I don't need it for uni as I wanna do maths.

To be honest if your good at maths you'll find it easy as most people struggle with Unit 5 as it's lots of calculations. It is harder but alot more interesting. If you dropped chemistry what would your subjects be?
Reply 1899
Avatar for Smuu
Smuu
13
What is the best way to revise module 4?:smile:


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