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Equilibria, Energetics and Elements (F325) - June 2011 Exam. watch

1. Well guys, this is it, it's almost all over; two years of long and arduous chemistry work has now boiled down to this final exam... good luck everyone!
2. (Original post by darkiee)
The long questions, worth like 7-11 marks where you have to explain yaself well
yes I know but what would we have to explain for LE and SEP which is 10 marker!
3. (Original post by arvin_infinity)
1/O2 + H2O + 2e- --------> 2OH- +0.4V
• 2H2O + 2e- --------> H2 + 2OH- -0.83V

!! so I need to memorise this. Obviously not those electrode potential!
Someone tell me what else I need to know!

SOmeone put question relevant to this
Just done
4b in jan 11
Couldnt deduce the half cell !! need someone to explain this to me!!

+Rep
You notice the electrode potentials?
Rule is that the Less Positive Terminal has been Oxidised, Oxidise is Loss of electrons, thus it goes the opposite way, but the top one is actually meant to be -0.83 not 0.4v, you mixed them around am I guessing...

The Half Cell cuts down to this:

H2+2OH--->2H2O + 2E- (Oxidised Equation)
1/2 O2 + H2O + 2E ---> 2OH- (Reduced Equation)

Balacing out, Cancelling and Overall equation:
H2+1/2 O2 --> H20.

Moar?
4. Quick question, do you put h20 in kc equilibrium and kstab or not? Someone answer please!
5. equlibrium and the Kc is probably going to come up as well with a nice calculation
6. (Original post by SmartFool)
Quick question, do you put h20 in kc equilibrium and kstab or not? Someone answer please!
You leave it out of kstab
7. (Original post by SmartFool)
Quick question, do you put h20 in kc equilibrium and kstab or not? Someone answer please!
In Kc yes, Kstab no because water is in such excess the amount you add is insignificant.

I think...
8. A BUFFER SOLUTION IS A SOLUTION THAT RESISTS CHANGE IN pH WHEN A SMALL QUANTITY OF ACID OR ALKALI IS ADDED
9. (Original post by SmartFool)
Quick question, do you put h20 in kc equilibrium and kstab or not? Someone answer please!
No H20 in K stab.
10. (Original post by intellectual1)
A BUFFER SOLUTION IS A SOLUTION THAT RESISTS CHANGE IN pH WHEN A SMALL QUANTITY OF ACID OR ALKALI IS ADDED
It 'minimises' pH changes, chemistry exams are pretty pedenatic usually, so text book deffinitions are best.
11. just wanted to clarify a few things before the exam..hope someone can help
okay so,

1) the rate constant is only affected by temperature right?
2) when the temp increases and the Kc value decreases = exothermic (forward reaction)
when the temp increases and the Kc value increases = endothermic (forward reaction)
(Kc only affected by temp)
3)Could anybody explain the actual role of the salt in buffer reactions, i know it dissociates to produce the conj. base but is that it?

(im just going through the spec, so il write some more if theres anything else that slightly bothers me)
good luck everyone!
12. I dont mind anny quection as long as its not buffer!!!!
13. I'm struggling to understand free energy. Can someone explain it to me, please?
14. (Original post by monkeyDace)
I dont mind anny quection as long as its not buffer!!!!

i mean for yourself so that we understand as well as you lol
15. Do we need to remember colours and oxidation states? What about redox equilibria such as MnO4 and Fe etc?
16. (Original post by monkeyDace)
I dont mind anny quection as long as its not buffer!!!!
Ha, I'm praying for buffers..we'll see who gets their wish xD
17. is the rate constant only affected by temperature? Can someone answer?
18. (Original post by Flux_Pav)
is the rate constant only affected by temperature? Can someone answer?
yep
19. Is the colour change for MnO4/Fe equilibrium from dark purple to pale pink??
20. (Original post by 123trident)
I'm struggling to understand free energy. Can someone explain it to me, please?
Which part?
Just remember the equation

^G= ^H - T^S

(Those odd triangles are meant to represent delta.)
If you're asked to calculate minimum feasible temp, then make the whole equation equal 0 and solve for T, basically algebra

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