Aqa chem 4/ chem 5 june 2016 thread

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Reply 2660

idk97

Im sure c2o4 did make c02?

Reply 2661

Azzer11

Original post by Aerosmith

Are you talking about the enthalpy and entropy calculations? If so, you're right! We didn't **** up, the rest did

Are you sure? It made sense to me in the exam but I'm not so confident now.

Reply 2662

vinchy

Original post by OloMed

The overall equation is:

H2 + 1/2 O2 ----> H2O

imcreasing conc of either H2 or O2, or increasing pressure, would all shift the equilibrium to the RHS, so EMF increases

I got that because for standard enthalpy i used SO2+1/2O2.> SO3
GOT -98.5KJMOL-1

Reply 2663

Suits101

Original post by K2Cr2O7

Didn't the question say find delta S and delta H for THIS reaction. Meaning they were asking for values for the exact equation they gave ???

Im not sure as i cant remember the question exactly.

Original post by Azzer11

There seems to be nobody that did the same as us, so maybe we ****ed up? :frown:

The question asked you to calculate the STANDARD enthalpy and entropy change, which was asked on Jan 13 I believe and you had to divide by two.

Reply 2664

girl :D

last exam tomorrow im gna spend all day watching game of thrones and eating pizza lol im soo exhausted :biggrin:

Reply 2665

sockface

prediced grade boundries... opinions please

Reply 2666

JC25

I forgot to multiply the hydration enthalpy of the chloride ion by 2 so ended up with an endothermic deltaH solution which is wrong. How many marks do you reckon I'd get for the solubility question having made the error in the previous q? Would I get many follow through marks?

Reply 2667

idk97

was the enthalpy of solution 775 (something like that) ??

Reply 2668

Osalim1998

Original post by vinchy

delta G got -65.1

thing is though, the given values for the question if you didnt get an answer was -250. not dividing by two gave you a closer answer, thats why im thinking you dont have to divide

Reply 2669

Azzer11

Original post by Suits101

The question asked you to calculate the STANDARD enthalpy and entropy change, which was asked on Jan 13 I believe and you had to divide by two.

If you're right, I love you.

Reply 2670

Cadherin

Original post by Azzer11

If you're right, I love you.

Divide what by 2??

Reply 2671

Suits101

Original post by JC25

As long as explanation was right, you should be fine.

Reply 2672

tbh12

Original post by Osalim1998

thing is though, the given values for the question if you didnt get an answer was -250. not dividing by two gave you a closer answer, thats why im thinking you dont have to divide

No it wasn't. -250 was given value for delta H.

Reply 2673

TheGeekGal

It was an okay paper, I made quite a few silly mistakes. With method marks and ecf, hopefully I haven't lost more than 30 :frown:

if I got 70 on both paper, and a C and hopefully a B/A from my resit from last year. Aswell as an A on course work and a C on course work this year. Could I scrape an A overall??

Reply 2674

Kay Fearn

Original post by vinchy

I got that because for standard enthalpy i used SO2+1/2O2.> SO3
GOT -98.5KJMOL-1

It wanted enthalpy change of the reaction not standard enthalpy of formation?

Reply 2675

Suits101

Original post by Cadherin

Divide what by 2??

Did you said SA has an effect on emf?

Reply 2676

Suits101

Original post by Kay Fearn

It wanted enthalpy change of the reaction not standard enthalpy of formation?

Enthalpy change can be calculated from standard enthalpy of formation, which is what you were given and used.

Reply 2677

username1142365

Original post by RefusedAccess

Question stated that solubility is defined as the amount of solid able to dissolve in water, so as it is an endothermic reaction, more MgCl2 is produced if you increase temperature, hence solubility is increased

Why is it endothermic if DHsolution for the forward reaction was a negative value?

Reply 2678

Paddycat12

Original post by koolgurl14

Should I do an unofficial or is there already done unofficial ms or anyone started doing one

please do one :smile:

Reply 2679

Azzer11

Original post by Cadherin

Divide what by 2??

The equation they gave you for the Contact Process involved the formation of 2 moles of SO3. So I halved the moles to get SO2 +1/2O2 ----> SO3 and used this equation to work out enthalpy/entropy. Not 100% confident it was the right thing to do.