OCR Chemistry A F322 Chains, Energy and Resources Wed 23 May 2012

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I don't understand about the shifting of the position of equilibrium.

How do you know when it shifts to the left or right?

If you increase temperature, concentration or pressure on the reactants, which way would that shift the position of equilibrium and why?

So confused >.<

do you remember Chatelier's principle?

it says that when there is a change in the conditions of a reaction in dynamic equilibrium, the position of equilibrium will change to minimise the change.

So when the temperature is increased, the position of equilibrium will move in direction of the endothermic reaction. So for the Haber process, where AH is negative for the forward reaction, the reverse reaction is therefore endothermic, and so position of equilibrium would move to the left, producing more reactants.

When concentration of reactants increases, the position of equilibrium moves to the right, this is to produce more product, or to react more reactant, if that makes sense. I know these are quite complicated concepts, but have a look through the textbook and try to understand, because it nearly always comes up.

When you increase pressure (only affecting reactions involving gases remember), the position of equilibrium will move towards the side where there are less gaseous moles. So more NH3 would be produced in the Haber Process. This is because when there are less moles of gas in the same volume, molecules are less close together, pressure falls.

Reply 981

nadzrahman26

Original post by Optical

Anyone else using the CGP AS Chemistry revision guide for this exam?

yeah i am i actually find it really useful the way it breaks everything down x

Reply 982

godknows

Original post by master y

god knows

alright 'master' :smile:

Reply 983

CosmicVengeance

Original post by nadzrahman26

yeah i am i actually find it really useful the way it breaks everything down x

Yup

but im going into Mark schemes now just learn them probably ateast 20marks worth similar will come up, no gaurantee as we saw with bio f322 xD

Reply 984

MrNeilPatel

Original post by kimsiclez

The Position of Equilibrium always shifts in the direction that will oppose this change ( Le Chatelier's Principle ); I'll do some examples:

For Concentration is increased, the Position of the Equilibrium will shift to the side where there is a low Concentration of molecules. For example, lets say that the Reactants have a High Concentration, to oppose this change we increase the Concentration of the Products; so therefore the Position of Equilibrium will shift to the Product Side

Pressure will only effect the Position of the Equilibrium if there are any gases present in the reaction. When we increase the Pressure, the Position of Equilibrium will shift to minimise this change; and to see which direction it moves to we must calculate the number of Moles of Gases on either side of the equation. For example, lets say we increase the Pressure on the whole system; and the total Moles of Reactants is greater than the total Moles of Products; the Position of Equilibrium will shift towards the Products; as there are fewer moles of substances

Temperature will affect the Position of the Equilibrium depending on whether the Forward or Backward reaction is Endothermic or Exothermic. For example, lets say in a reaction, the forward reaction is Exothermic; and we decide we would like to increase the temperature. When we do this, the Position of Equilibrium must move in the direction that decreases this increase in temperature. Therefore, the position of the Equilibrium moves backwards as the Backwards reaction in Endothermic and takes in heat.

Hope that Helps :biggrin:

Reply 985

Oromis263

Just thought I'd come and post these in here, I did make a thread for them a week ago, or so, but I don't think many people saw it. I know it's incredibly late, but these are the notes I used when I sat this exam last summer! Good luck with it tomorrow everyone!

https://sites.google.com/site/mathslab9000/home/chemistry/f322---chains-energy-and-resources

Reply 986

rival_

You people are so radical how you going revise from markschemes #swagg

Reply 987

kenann

i got 69 UMS points in jan, sitting the paper before this. how many UMS will i need to average out the AS year to an A? even more ambitiously, how many will i need to get to make it enough for me to get an A* next year, assuming i get around 90% in both chem exams next year?

69 is a B btw

Reply 988

master y

Original post by MrNeilPatel

Heres a list of all the Definitions in Unit 2:

https://www.dropbox.com/s/1gitgelej17geoj/Chem%20Definitions.docx

thanks neilu beta :P

Reply 989

otrivine

is the ocr specimen paper meant to be the hardest?

Reply 990

Conal09

If it says "outline... blah blah" in the specification, does that mean we have to know that point, or just be able to deduce it from the question, if that makes sense?

Reply 991

MrNeilPatel

Original post by master y

thanks neilu beta :P

Wait, we don't tell me you go my school as well ?

Reply 992

kenann

anybody here go holy cross/bury college in manc?

Reply 993

master y

Original post by MrNeilPatel

Wait, we don't tell me you go my school as well ?

lol which skl?

Reply 994

CosmicVengeance

Original post by kenann

anybody here go holy cross/bury college in manc?

bury college, is that in bham ?

Reply 995

MrNeilPatel

Original post by master y

lol which skl?

Lol sorry, the way you said "Thanks Neilu Beta" reminded me of someone at my school :biggrin:

Reply 996

Oromis263

Original post by kenann

It depends what you got on your coursework. I got 62 ( :colondollar:

) last year on F321, but didn't really want to resit it, so worked harder for F322 and got an A.

To get an A, you need 171 UMS between your coursework and this exam, so 171/210. :smile:

To get an A*, you only need to average 90% at A2. You can, theoretically, get 60% at AS, and 100% at A2, and come out with an A* overall! :smile:

Good luck!

Reply 997

master y

Original post by MrNeilPatel

Lol sorry, the way you said "Thanks Neilu Beta" reminded me of someone at my school :biggrin:

noice.

Reply 998

Pride

Original post by Conal09

If it says "outline... blah blah" in the specification, does that mean we have to know that point, or just be able to deduce it from the question, if that makes sense?