ocr a f325 revision thread

some hard stuff, but definitely an interesting module minus rates

Hi MedMed 12 how are you?

want to revise F325?

Hey otrivine,

well thanks yourself?

Sure! Erm I dont know f215 as well as you but we can give it ago!


define operon (2 marks)

explain the advantage of synthesising beta galactosidase when lactose is present only (2 marks)


T


why did I take biology ? haha!

Here's a couple of questions:

What must you never include in a Kc equation and why?(2)

What does the pKa value indicate about an acid's strength?(1)

thanks , not biology I mean F325, chemistry unit 5 questions

1) In Kc equation you never include molecules/compounds that are in solid or liquid state this is because they are not in (equilibrium) constant, and because the particles are not able to spread because in solid and liquid the molecules are not able to move freely as compared to gases or in aqeous solutions,

2) Lower Pka value indicates that the strength of the acid is stronger

I think I'm blind haha!

Okay sorry about that hmmm what affects Kc and why? 2-3 marks

what is entropy?


when is a reaction feasible?



Outline the benefits of fuel cells? the disadvantages?


redox titrations - what colour changes happens with Mn?

Second one correct. For the first one that wasn't the answer I was thinking of but it sounds correct! I should have been more specific - I meant when the compounds are in aqueous (I've only ever done Kc in aq so I naturally assumed people would assum that too) you must eliminate water as it is in excess so much so its concentration outweighs all the other compounds'.

No worries

1) Kc is only affected by temperature, this is because Kc is an equilibrium constant and only gas and aqueous compounds/molecules are affected only by temperature. Kc increases if forward reaction is endothermic and Kc decreases if forward reaction is exothermic. Also, Kc is affected by temp as it affects the value of Kc , so if Kc< 1 then reactant side is predominant and Kc>1 is product favoured.

2) Entropy is the quantative measure of the degree of disorder in a system

3) A reaction is feasible if the value of deta G< 0 , the value of deta G is determined by the free energy equation/formula which is deta G= deta H - Tdeta S



4) The advantages of fuel cells= less pollutant and less co2 is released and greater efficiency. Also, is publically and poltically accepted (more).

disadvantages= uses toxic chemicals in their production, fuel cells have a limited life time and requires regular replacement and disposal following high production costs, the feasibility of storing a pressurized liquid and current adsorbers and absorbers have a limited life time.

5) It turns from purple (Mno4-) to almost colourless/ dilute purple ( Mn2+)

all correct
haha you make feel like I'm failing with your perfect answers to the bio and chem questions I ask you!
I really do hope you get the grades you want/need, you work so hard its unreal!

Hhaha thank, you are doing very well too


But I was unsure for question 1 to be honest, was my reason for why Kc is only affected by temp?

aha not well enough hows maths going? c4 right?

ahhh actually, I dont think they'll ask that question, my teacher gave it to us as a stretch and challenge. basically temp affect kc/kp as more or less product is produced, whereas the other factors such as conc, volume only affect position of equilibrium.

C4 is okish , a big jump from c3 but finding vectors a nightmare

What about u ?

I have the jan 2013 QP and MS, so if anyone wants it, just pm me your email and i'll send it to you