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OCR A Chemistry F322 Chains, Energy and Resources Thu 19 Jan 2012

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For the "why do CFCs still exist" question, I put they stay in the atmosphere for millions of years plus people still use them in fridges etc.

Is that right?

Reply 461

andrewpeters

Bit about decreasing temp with Boltzmann was a bit tricky. I drew another curve which had an earlier and higher peak.

Reply 462

holahola

Original post by otrivine

the one on calculatiing the question on enthalpy energy released thing for the last part c) did u get -134

Why is it minus

Reply 463

andrewpeters

Original post by Eternal Rest

For the "why do CFCs still exist" question, I put they stay in the atmosphere for millions of years plus people still use them in fridges etc.

Is that right?

I put that, but I also said we're still using HCFC's. It asked for 2 reasons.

Reply 464

andrewpeters

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Reply 465

otrivine

Original post by holahola

Why is it minus

it was minus cause 19-32 something everyone got -134?

Reply 466

dee11

Original post by holahola

Why is it minus

its cause it was an exothermic reaction, and exothermic reactions release enery, hence the increase in temperature

Reply 467

Lyd.Naomi

Original post by faz_341

679 + ? = -184
so ? equals 862
since there is 2hcl divide by two = 431.5

when you're doing that algebra:

you would have to put a negative sign infront of 431.5 for that to work:

-836 + 679 = - 184

The bond enthalpy would be positive so it would have to be during the hess's law calculation that you switch the sign.

I switched the sign of the 679 instead.

so: x - 679 = -184

x= 495

then divide by 2 and get 247.5 ....

So I guess it all depends which part of the calculation you reverse the sign of...

(edited 12 years ago)

Reply 468

otrivine

Original post by dee11

its cause it was an exothermic reaction, and exothermic reactions release enery, hence the increase in temperature

how are you for the question suggest why HFCL4 one cant remeber the compound bt it said why used in aerosol thing that question? i wrote cause it does not deplete the ozone layer?

Reply 469

dee11

I totally forgot the definition for sterioisomers

what did people get for identifying compond J using the infared spectum ques?

Reply 470

dee11

Original post by otrivine

how are you for the question suggest why HFCL4 one cant remeber the compound bt it said why used in aerosol thing that question? i wrote cause it does not deplete the ozone layer?

Heya, yeah im alright thanks :smile:

and yourself?

oh for that question, if i think its the right one your asking about. I put that CLC'S were non toxic,

think it was to do with the properties of CFC's that made them ideal for use

Reply 471

otrivine

Original post by newbie1993

but it is CFCS that deplete the ozone layer :s

no it was the question they gave us already 2 examples and they said give another reason? am i wrong and for the question second one i said insoluble in water and the last ne suggest why cfcs are still present even banned i talked about planes and cars ?

Reply 472

newbie1993

Original post by tomdodsworth

I said that it wasnt polar and couldn't dissolve...could be completely wrong lol :smile:

ooohhh...

i put that the c-f and c-cl bond are very polar and and so repel the OH electrons....crikeyy :s got that wrong :frown:

Reply 473

member403966

Original post by nffc-b

And what did everyone get for why process one is better than process two?
I got because it has 100% atom economy so no waste
Can be done in lower pressure so it will cost less and be less of a hazard
And I wasnt too sure about the last one, but I put that it takes in carbon monoxide and converts it into usefull products and that was a poisonous gas and then i blagged on about the environment

PROCESS 2 USED CRUDE OIL! Non- renewable energy source, Methanol is renewable.

Reply 474

otrivine

Original post by dee11

Heya, yeah im alright thanks :smile:

and yourself?

oh for that question, if i think its the right one your asking about. I put that CLC'S were non toxic,

think it was to do with the properties of CFC's that made them ideal for use

yh i guessed on that and for the second part i said insoulbe in water ? and the suggest one at the end why still cfcs are present i said planes and cars cause everday people use them?

Reply 475

Eternal Rest

Original post by dee11

I totally forgot the definition for sterioisomers

what did people get for identifying compond J using the infared spectum ques?

I got an aldehyde with an Mr of 86.

I also saw it could be a ketone aswell, but I stuck with the aldehyde. I think it was like pentanal or something.

For the stereoisomer definition, I put they have the same structural formula but a different arrangement of atoms in space.

(edited 12 years ago)

Reply 476

Eternal Rest

Original post by andrewpeters

I put that, but I also said we're still using HCFC's. It asked for 2 reasons.

Yeah I put 2 reasons.
1st one was that they stay up there for millions of years
2nd one was that people still use them like in fridges.

Reply 477

dee11

Original post by otrivine

yh i guessed on that and for the second part i said insoulbe in water ? and the suggest one at the end why still cfcs are present i said planes and cars cause everday people use them?

I wrote down that CFC'S stay in the atmosphere for a long period of time because they have low reactivity, and also because they arent broken down until they reach the stratosphere? I wasnt too sure on that ques :s-smilie:

Reply 478

asif123

Overall a very generous paper but I have a strong suspicion that the grade boundaries will be sky high...something like 80-85+ for an A. A couple of iffy questions like the catalyst one...I know catalyst doesn't affect the equilibrium but wouldn't it slow down the reverse reaction if there was no catalyst as a catalyst speeds up both forward and reverse reactions equally. Did anyone get propanal/C5H10O for the one where you had to analyse I.R and come up with a structure and for the CFC's no presence of a C-H bond....oh and that CFC's are non toxic as you are able to inhale them blah blah...Let me know if anyone got any similar answers please..haha :smile:

Reply 479

otrivine