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

You know for the redox titration calculations in the transition metals bit, do they provide us with the relevant equations necessary to do the calculations??

We're expected to know all the half equations.

Reply 241

student777

8

Original post by Vidja

I'm having a bit of trouble getting my head around Born-Haber cycles. I know they're used to calculate the Lattice enthalpy, but....what are they? Like, when do they take place? Do all of those reactions (First ionisation, atomisation, formation) happen whenever a lattice enthalpy is formed?
So if I reacted chlorine with potassium all this atomisation and first ionisation energy happens 'behind the scenes'?

The whole point of a Born-Haber cycle is to work out enthalpy changes that just wouldn't happen in real life.
The steps in a the cycle do not happen if you're just in a chemistry lab mixing stuff together in test tubes. However the enthalphy change is the same whatever route you take- the one that actually happens in the lab or the imaginary one in the born-haber cycle :smile:

Reply 242

intellectual1

3

For the new A2 examinations, this places a much greater emphasis on application of knowledge and understanding

Success though will not come from purely learning all the specification content and memorising mark schemes. Although this will help, application will also be tested using questions set in novel contexts. Candidates do seem to have problems combining two half-equations and it was perhaps not surprising that very few candidates were able to perform the more difficult task of deriving the other half-equation taking place in the cell.
Enthalpy change of neutralisation is a new requirement of this specification but there was clear evidence from blank responses on a significant number of scripts that this topic had not been revised.

http://www.ocr.org.uk/download/rep_11/ocr_58284_rep_11_gce_jan.pdf

Looks like it'll be a tough challenging paper, some questions are completely new and not seen in past questions and it is concerned with applying ones knowledge.

Reply 243

INeedToRevise

8

Original post by intellectual1

We're expected to know all the half equations.

What pages are they on in the OCR textbook??

Reply 244

Rosi M

11

Original post by intellectual1

For the new A2 examinations, this places a much greater emphasis on application of knowledge and understanding

Success though will not come from purely learning all the specification content and memorising mark schemes. Although this will help, application will also be tested using questions set in novel contexts. Candidates do seem to have problems combining two half-equations and it was perhaps not surprising that very few candidates were able to perform the more difficult task of deriving the other half-equation taking place in the cell.
Enthalpy change of neutralisation is a new requirement of this specification but there was clear evidence from blank responses on a significant number of scripts that this topic had not been revised.

http://www.ocr.org.uk/download/rep_11/ocr_58284_rep_11_gce_jan.pdf

Looks like it'll be a tough challenging paper, some questions are completely new and not seen in past questions and it is concerned with applying ones knowledge.

We'll be sitting the 3rd paper for this series. How low do you reckon the grade boundary will be for an A grade? Jan 11 was very low.. 65. Something like that would be great.

Reply 245

tripodd

Could anyone please explain to me the thinking behind 1(a)(iii) on the specimen paper? It's a one marker and I'm not getting the answer. Thanks :smile:

Reply 246

student777

8

Original post by tripodd

Could anyone please explain to me the thinking behind 1(a)(iii) on the specimen paper? It's a one marker and I'm not getting the answer. Thanks :smile:

If you look at the question, it says it's the rate of formation of HCHO, and you want the rate of formation of O2. So you have to divide by four, because there are 4 halves in 2. Does that make sense? :smile:

Reply 247

tripodd

Original post by student777

If you look at the question, it says it's the rate of formation of HCHO, and you want the rate of formation of O2. So you have to divide by four, because there are 4 halves in 2. Does that make sense? :smile:

Ah hah! I was doing /2 because I assumed it was formation of O2. Thank you :-]

Reply 248

intellectual1

3

Original post by Rosi M

We'll be sitting the 3rd paper for this series. How low do you reckon the grade boundary will be for an A grade? Jan 11 was very low.. 65. Something like that would be great.

At a Chemistry student revision confernce last Dec, the examiners Mike and John said that in three years, the entire specification is assessed. So we're half way through the F325 papers, meaning alot of content has'nt been asessed yet.

Probably low boundaries since Stretch and Challenge questions are definately more concerned with application of knowledge and understanding. By all means do past papers, but the F324 and F325 exams are assessing understanding of concepts and applying knowledge. Memorise the textbook and think about the question in the context :wink:

Reply 249

sportycricketer

What does everyone say that we predict the sort of questions that we're gonna be tested on? Would be good to have everyone's perspective on this :biggrin:

Reply 250

michael clayton

15

Original post by intellectual1

For the new A2 examinations, this places a much greater emphasis on application of knowledge and understanding

Success though will not come from purely learning all the specification content and memorising mark schemes. Although this will help, application will also be tested using questions set in novel contexts. Candidates do seem to have problems combining two half-equations and it was perhaps not surprising that very few candidates were able to perform the more difficult task of deriving the other half-equation taking place in the cell.
Enthalpy change of neutralisation is a new requirement of this specification but there was clear evidence from blank responses on a significant number of scripts that this topic had not been revised.

http://www.ocr.org.uk/download/rep_11/ocr_58284_rep_11_gce_jan.pdf

Looks like it'll be a tough challenging paper, some questions are completely new and not seen in past questions and it is concerned with applying ones knowledge.

I very much agree with this- by learning the spec to a sufficient standard you can probably scrape an A but to get the A* you really need to be able to apply knowledge to unknown situations.

Reply 251

wilsea05

1

Original post by sportycricketer

I meant "so NOT that great" haha.. lol that's pretty good. If you get an A* in it (which you most probably will) are you gonna take a gap year? And what are you doing other than Bio and Chem? :P

nahh not taking a gap year, hopefully going to sheffield to do biomedical sciences.
i do spanish, it is the bane of my life at the moment! aha what about you? and what are your plans for next year?

Reply 252

intellectual1

3

Original post by sportycricketer

What does everyone say that we predict the sort of questions that we're gonna be tested on? Would be good to have everyone's perspective on this :biggrin:

Kinetics calculation/half life theory
Equilbria calculation and explanations of the theory
Energetics definitions and calculations
Entropy
Transition metal colours/configurations
More calculations, such as Redox titration ones
Organic from AS/A2 remember it is a third SYNOPTIC!

Reply 253

voices1

Could some explain free energy?
I know the facts and i have applied to questions which i have answered them correctly. However i do not understand them
1-exothermic reaction, despite entropy decrease, enthalpy contributes more to free energy. Does this mean enthalpy is positive?
2- exception at high temp, entropy decreases. TAS becomes more negative than enthalpy. eventually enthalpy-t^s Becomes postive
does this mean only at high temp, during exothermic reactions- reaction is never feasible?
the quation will be negative=(+)-(+*-)

cud some1 kindly help me please

Reply 254

sportycricketer

Original post by voices1

Could some explain free energy?
I know the facts and i have applied to questions which i have answered them correctly. However i do not understand them
1-exothermic reaction, despite entropy decrease, enthalpy contributes more to free energy. Does this mean enthalpy is positive?
2- exception at high temp, entropy decreases. TAS becomes more negative than enthalpy. eventually enthalpy-t^s Becomes postive
does this mean only at high temp, during exothermic reactions- reaction is never feasible?
the quation will be negative=(+)-(+*-)

cud some1 kindly help me please

?H ?S ?G Feasibility
-ve +ve Always -ve Feasible
+ve -ve Always +ve Never Feasible
-ve -ve -ve at low temp Feasible at low temp
+ve +ve -ve at high temp Feasible at high temp

Hope this helps :smile:

Original post by intellectual1

Kinetics calculation/half life theory
Equilbria calculation and explanations of the theory
Energetics definitions and calculations
Entropy
Transition metal colours/configurations
More calculations, such as Redox titration ones
Organic from AS/A2 remember it is a third SYNOPTIC!

Isn't that pretty much everything? haha :P

Reply 255

airdoc

3

Original post by sportycricketer

no problem :smile:

.. the thing with maths in the old papers is that it can either easy or very hard. How many qs have you done off the doc then? :smile:

haha yeah. I've done 110 questions :biggrin:

You?

Reply 256

voices1

Original post by sportycricketer

?H ?S ?G Feasibility
-ve +ve Always -ve Feasible
+ve -ve Always +ve Never Feasible
-ve -ve -ve at low temp Feasible at low temp
+ve +ve -ve at high temp Feasible at high temp

Hope this helps :smile:

Isn't that pretty much everything? haha :P

So for exothermic reaction enthalpy outweighs entropy so reaction occurs free energy is less than zero. Correct?
you said -ve +ve Always -ve Feasible
will temperature need to be negative so (-ve)-(-temp*postive entropy) for a negatvie free energy, correct?

I'm confident with all calculation and written work regarding this but apart from the calculations most of it is memorizing that pure understanding with regards to free energy.

e.g for an endothermic reaction, entropy must be high enuf to outwiegh enthalpy and temp must be high.... can apply to particular reactions but have no clue what that means