****Leaving Certificate Chemistry [All Levels] Before and After Discussion****

jellytots95

AtomicKoala wrote: »

I got ΔH = -2877.3 kJ mol^-1, did anyone else?

EDIT: I checked Wikipedia. I think your value is for propane:

http://en.wikipedia.org/wiki/Butane_(data_page)

http://en.wikipedia.org/wiki/Propane_(data_page)

Wikipedia says it -2877.

I got this

EoghanIRL

In equilibrium question did anyone get x as 0.4 and 1.8 as number of moles .

Also I said kc is temperature dependent and pressure independent .

Anyone else get this ??

WoolyAbyss

little sis... wrote: »

Yeh me too haha wasted time going halfway then realised I had no clue what was going on. It was a pitty because all the other parts were nice!
Yeh I did 9 excluding that too

I don't think those kinds of calculations for pH were in the book I used I definitely don't remember it anyway.

MacBizzle

EoghanIRL wrote: »

In equilibrium question did anyone get x as 0.4 and 1.8 as number of moles .

Also I said kc is temperature dependent and pressure independent .

Anyone else get this ??

Pressure independent? an increase/decrease in pressure only has an effect if there are different number of moles on each side of the equation

little sis...

How come? I re-checked it again aswell? I'm 100% sure I did it for butane aswell not propane

EoghanIRL

Other answers I got :

X as 7 in q1
Percetage water crystallisation as 54.0something .cant read my writing .

Q2 i got 45.9 grams for maximum yield .

MacBizzle wrote: »

Pressure independent? an increase/decrease in pressure only has an effect if there are different number of moles on each side of the equation

You are thinking of the completely wrong thing .
It's the value of kc not the reaction. Sorry

Marko1011

MacBizzle wrote: »

Pressure independent? an increase/decrease in pressure only has an effect if there are different number of moles on each side of the equation

No, Kc is completely independent of pressure no matter how many molecules there are on either side of the equilibrium. Kc only ever changes with temperature, in this case it decreased with an increase in temperature.

EoghanIRL

Marko1011 wrote: »

No, Kc is completely independent of pressure no matter how many molecules there are on either side of the equilibrium. Kc only ever changes with temperature, in this case it decreased with an increase in temperature.

This is what i said .
He is thinking of the reaction not kc value .

MacBizzle

EoghanIRL wrote: »

You are thinking of the completely wrong thing .
It's the value of kc not the reaction. Sorry

Change in presurre had no effect on Kc because there were the same number of moles on each side

EoghanIRL

MacBizzle wrote: »

Change in presurre had no effect on Kc because there were the same number of moles on each side

Lul

WoolyAbyss

EoghanIRL wrote: »

Other answers I got :

X as 7 in q1
Percetage water crystallisation as 54.0something .cant read my writing .

Q2 i got 45.9 grams for maximum yield .

Ya I got the same as you for question 1
I can't remember what I got for question two but it looks familiar.

WoolyAbyss

jellytots95 wrote: »

I got this

Damn it :mad: I did it for propane now that I think about it. I'm so happy I did that extra question now.

Inspector Coptoor

-2887.3 kJ/mol

54.6% water crystallization
The value of x was 6.97

4.59g Mac yield for soap.

I still can't believe how straight forward it was.

The Stoichiometry question in 10 b could have been on an OL paper.
12.6g - Mr was 252 so 0.05 moles and away you go from there.

Really hoping my students get a shed load of A1s

accountname

EoghanIRL wrote: »

Other answers I got :

X as 7 in q1
Percetage water crystallisation as 54.0something .cant read my writing .

Q2 i got 45.9 grams for maximum yield .

4.59 grams for the soap, right? :rolleyes:

WoolyAbyss

I can't remember what I got for the Kc but did any one get 18 in the square root part for the quadratic?

Wanderer41

accountname wrote: »

4.59 grams for the soap, right? :rolleyes:

I got 4.59 grams for that question.
Overall I think it was okay, really hoping I got an A1. I think it was quite manageable, just hoping that I didn't omit things or put silly things down in my panic.
I did either 8 or 9 questions, can't remember. Spent loads of time studying the option and I didn't even look at it today.. really should have because just looking at Q11, the b part is really easy and a isn't bad either. Typical me :L No point thinking of what I should have done now though. Just glad it's over

TooMuchStudy

MacBizzle wrote: »

You didn't divide by 2 probably

Ah yes, I multiplied by two at the start to get rid of the half on the o2, will I lose many marks for this?

MacBizzle

TooMuchStudy wrote: »

Ah yes, I multiplied by two at the start to get rid of the half on the o2, will I lose many marks for this?

Nah, 1 or 2 I'd say.

Inspector Coptoor

3 marks I'd say or 0.75%

That question will have 12 or 15 marks and they are Lways awarded in 3s

rocco123

1 54.2% x=7
2 4.59g
3 74 seconds
4 S2O3 iodide one 1.96x10-4 grams
5 -2877.3
10c 3Cd+8H+2NO3= 3Cd+2NO+4H2O
Can anyone tell me if that last one is right?

WoolyAbyss

For the start of question 5 how many people said bohr?

Inspector Coptoor

rocco123 wrote: »

1 54.2% x=7
2 4.59g
3 74 seconds
4 S2O3 iodide one 1.96x10-4 grams
5 -2877.3
10c 3Cd+8H+2NO3= 3Cd+2NO+4H2O
Can anyone tell me if that last one is right?

10 c - that's correct.
Good work

Huell

Got x for q1 but didnt get percentage....a sh|te

TooMuchStudy

Inspector Coptoor wrote: »

3 marks I'd say or 0.75%

That question will have 12 or 15 marks and they are Lways awarded in 3s

One of the questions were to write down the formula and I wrote down the formula multiped by 2, would that be wrong?

MacBizzle

TooMuchStudy wrote: »

One of the questions were to write down the formula and I wrote down the formula multiped by 2, would that be wrong?

Nope, it's bad practice to have non-whole numbers our teacher said so you'll be fine

MacBizzle

WoolyAbyss wrote: »

For the start of question how many people said bohr?

Was it not Bohr?

Inspector Coptoor

No, it's not wrong at all, it's be balanced.
However, you must divide by.2 at the end to get the heat of combustion as it's for 1 mole, according to the definition, not 2.

Make sense?

MacBizzle wrote: »

Nope, it's bad practice to have non-whole numbers our teacher said so you'll be fine

I'll agree to disagree there.

The number of O2 molecules doesn't matter as it's in excess and has a value of 0kJ/mol, so 13/2 O2 is fine as it has no bearing on the answer.

As previously stated, a candidate will lose 3 marks for not diving by 2 at the end

TooMuchStudy

Inspector Coptoor wrote: »

I'll agree to disagree there.

The number of O2 molecules doesn't matter as it's in excess and has a value of 0kJ/mol, so 13/2 O2 is fine as it has no bearing on the answer.

As previously stated, a candidate will lose 3 marks for not diving by 2 at the end

Think he was saying I'll be fine for the question which says to write out the equation but thanks for your feedback!

Ellenom

What was the number of moles of N2 in Q.9?

MacBizzle

Inspector Coptoor wrote: »

I'll agree to disagree there.

The number of O2 molecules doesn't matter as it's in excess and has a value of 0kJ/mol, so 13/2 O2 is fine as it has no bearing on the answer.

As previously stated, a candidate will lose 3 marks for not diving by 2 at the end

Yeah, they're both fine. Our teacher just said at LC level ideally you should keep everything to whole numbers when balancing.