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Aqa chem 4/ chem 5 june 2016 thread

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Reply 2020

lahigueraxxx

Original post by jammypancake

anyone else *****ing one for tomorrow lol

Yup!! Literally praying it's nothing like chem4

Reply 2021

Jmedi

Original post by Glavien

How do you do this question?

ImageUploadedByStudent Room1466529618.015149.jpg

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Chromium equations starting from

Cr(H2O)3(OH)3 + 3H+ -> [Cr(H2O)6 ]3+

Cr(H2O)3(OH)3 + 3OH- -> [Cr(OH)6]3- + 3H2O

Reply 2022

Jmedi

Original post by Bloom77

Thank you
It did
But why don't you also x2 for 158 because 2 F are also produced

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Yeah two moles are produced but what it's doing it giving you bond dissociation enthalpy, which is that equation, which is the enthalpy change when one mole of covalent bond is broken hence no change needed.

Atomisation enthalpy stuff, where you would have x2 before probably is for when 1 mol of gaseous atoms is formed

Reply 2023

cookiemonster15

Original post by lahigueraxxx

Yup!! Literally praying it's nothing like chem4

I swear to god though, if it's anything like chem4 I'll scream. And probably cry.

Reply 2024

shiney101

Do we need to know the equations for the fuel cell in alkaline conditions?

Reply 2025

thenextchemist

Another oxidation question lol
I can't seem to do these simple ones 😭
Thank you!

ImageUploadedByStudent Room1466531044.922600.jpg

NH3 has no charge so that's 0
SO4 has an oxidation state of -2
So X + 0 -2 = 0
Therefore, X = +2
So is that how you get the answer?

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Reply 2026

SirRaza97

Original post by Super199

http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JAN13.PDF

3c.

why do you halve the oxygen value. I don't understand :frown:

Write out the equation of the reaction happening and you'll undertsand why. I've done it 2 ways here which gives the same answer:

Reply 2027

Jmedi

Original post by Bloom77

Another oxidation question lol
I can't seem to do these simple ones 😭
Thank you!

ImageUploadedByStudent Room1466531044.922600.jpg

NH3 has no charge so that's 0
SO4 has an oxidation state of -2
So X + 0 -2 = 0
Therefore, X = +2
So is that how you get the answer?

Posted from TSR Mobile

Yeah ligands like NH3 and H2O are uncharged and it shows the overall is 0, hence just 2+ to counter the SO4(2-)

Reply 2028

Super199

Original post by SirRaza97

Write out the equation of the reaction happening and you'll undertsand why. I've done it 2 ways here which gives the same answer:

See I tried writing out the equation, and I got the second one. I got the delta H as 89. But I don't get why you halve it, or in this cause you've doubled the temperature?

Reply 2029

thenextchemist

Original post by Jmedi

Yeah ligands like NH3 and H2O are uncharged and it shows the overall is 0, hence just 2+ to counter the SO4(2-)

THANK YOU

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Reply 2030

flylikeafly

what should I revise? Any predicitons

Reply 2031

zombaldia

Original post by emma_1111

Is lattice dissociation always -ve?

Lattice dissociation: bonds are breaking: Bond breaking releases energy: It is always positive!!

Reply 2032

nutcase13

Original post by flylikeafly

what should I revise? Any predicitons

if chem4 is representative, i would say absolutely anything could come up

Reply 2033

SirRaza97

Original post by Super199

See I tried writing out the equation, and I got the second one. I got the delta H as 89. But I don't get why you halve it, or in this cause you've doubled the temperature?

I haven't doubled the temp. I have doubled the enthalpy change. This is because in the second equation I am creating 2 lot's of water. So the energy required to create twice the amount will be twice the energy so deltaH is multiplied by 2.

In the first equation whichis how the mark scheme does it, is that you are creating 1 mol of water so deltaH is -242. The reason it's half of water because the first equation is 1/2O₂which means that the entropy must be half aswell.

Reply 2034

flylikeafly

Original post by nutcase13

if chem4 is representative, i would say absolutely anything could come up

yeah thats what I thought im just going over the book looking for sneaky things they could bring up but others seem to be discussing past paper questions

Reply 2035

jammypancake

if it asks for strongest/reducing agent, how do you know whether to say its like Zn or Zn2+?

Reply 2036

nutcase13

Original post by jammypancake

if it asks for strongest/reducing agent, how do you know whether to say its like Zn or Zn2+?

reducing agents are on the right hand side, and oxidising agents are on the left hand side

Reply 2037

420memeception69

I will be so disappointed if chem 5 is like chem 4. I don't care if the paper is hard but it's the fact that a lot of revision will have been wasted

Reply 2038

badaman

Original post by flylikeafly

yeah thats what I thought im just going over the book looking for sneaky things they could bring up but others seem to be discussing past paper questions