Quantitative equilibria analysis (1 Viewer)

[shazzam]

Hello, if anyone can answer these questions PLZ help. Basically I don't know how to do questions where you need to mind the concentraions of reactants or products for a system at equilibrium...

e.g. 1 mol of CF4 reacts with 1 mole of CO2 to form COF2. At 200degreesC an equilibrium is established in a 5L vessel. At equilibrium 0.4mol of COF4 have been formed., calculate the equilibrium concentrations of the reactamt gases

e.g. for the equilibrium COCl2(g) <--> CO(g) + Cl2(g)
a) Find the concentration of Cl2 when there is 0.2 mol of CO and 0.8mol of COCl2.
b) 0.2mol of CO is injected into the reaction vessel and the system adjusts itself to a new equilibrium. Find the concentration of each gas at the new equilibrium.

My brain hurts from this confusion, please someone enlighten me.

 

[mervvyn]

for 1) you need to write a proper equation before you can do anything else...
2) a) is there any more information in the question? like a value for the equilibrium constant (K) or an initial condition? i think there is 0.2mol Cl2, because there is 0.2mol of CO... it would definitely be the case if it started with 1mol of COCl2 and then it told you that it was at equilibrium with 0.8/0.2, so yeah...
b) need part a) to be able to do it

 

[shazzam]

I did in fact write out the equation for the first question. If the reaction as written were to go to completion, 1 mol of CF4 + 1mol of CO2 --> 2mol of CIF4. However I don't see how I can use this in my calculations, though I know it is neccessary.

For the second equation, yes sorry I neglected K, which you have to find (actually you're meant to do this using the information given), it should be 0.05,. In addition the reactions occur in a 1L flask. That is all the inforamtion you are given, all on a fairly simple graph.

so, any ideas?

 

[mervvyn]

ok, for 1: (i hope that is the right answer)

 

[mervvyn]

For 2:
When there is 0.8 COCl2 and 0.2 CO, and K = 0.05, from PORK (see pic), so [Cl2] = (0.2 x 0.05)/0.8 = 0.0125mol
Except that doesn't seem right.. maybe it is, i don't know
for b), assuming it is right
K= 0.05, new conc of CO is 0.4..... ah...i'm screwed. sorry, i don't know what the next step would be.

 

[xiao1985]

ok, for 1: (i hope that is the right answer)

uhm i have to say that i disagree... since both side have the same amount of gases, then the volumn will not change equilibium posiition at all... basically, all u need is:

[COF2] ^2
-----------------
[CF4][CO2]

@eqlbm...
cof2 => 0.4
cf4 => 0.8
co2 => 0.8

therefore, k should be around 0.125

 

[shazzam]

ehh, nice try but answer is [CF4] = [CO2]=0.16mol/L

this is question 7 on pp226 of Thickett's Chemistry Pathways 2 ,2000 Edition

the other question is q8, so if you wanna take another stab at it...

 

[xiao1985]

For 2:
When there is 0.8 COCl2 and 0.2 CO, and K = 0.05, from PORK (see pic), so [Cl2] = (0.2 x 0.05)/0.8 = 0.0125mol
Except that doesn't seem right.. maybe it is, i don't know
for b), assuming it is right
K= 0.05, new conc of CO is 0.4..... ah...i'm screwed. sorry, i don't know what the next step would be.

uhm isn't 0.2 mol of CO and 0.8 mol of cocl2 present??? so shouldn't cl2 be 0.2 mol???

 

[shazzam]

[COF2] ^2
-----------------
[CF4][CO2]

@eqlbm...
cof2 => 0.4
cf4 => 0.8
co2 => 0.8

therefore, k should be around 0.125

sorry xiao but the k is apparently 0.25 (no idea, does not work with my calculations). Also how do you know the concentration of CF4 and CO2

 

[xiao1985]

ehh, nice try but answer is [CF4] = [CO2]=0.16mol/L

this is question 7 on pp226 of Thickett's Chemistry Pathways 2 ,2000 Edition

the other question is q8, so if you wanna take another stab at it...

didn't i get it right then??? altho i didn't convert it to mol/l...

btw shazzam, in ur q, u put cof4 =p

 

[xiao1985]

sorry xiao but the k is apparently 0.25 (no idea, does not work with my calculations). Also how do you know the concentration of CF4 and CO2

AHAHHAA, lolz, dude, if u'd see my answer, u'd call me an idiot ... i wrote:

0.16/0.64 = 1/8 = 0.125 =p

regardin the conc, my lecturer told us to use ice:

Initial
Change
Equilbrm

cf4 co2 cof2
1 1 0
-x -x + 2x
1-x 1-x 0.4 = 2x

therefore x = 0.2 etc etc

 

[shazzam]

didn't i get it right then??? altho i didn't convert it to mol/l...

btw shazzam, in ur q, u put cof4 =p

uh haha.. sorry i am so exasparated that I can not proof read my typos, but I am quite sure everything is else is correct other than this place where i typed CIF2 instead, nwasys I meant COF2.

um, i don't know how you knew the concentration of the reactant gases, that is my question, cos I don't know how to find that

 

[xiao1985]

concentration = number of moles / volume... that is 1 mole/ 5 litres... whereas, in this q, since both products and reactants have same moles of gaes, u can ignore volumn... but if u want to be accurate, u can always stick the volemn in..
btw, to ignore volumn, simply use mole as concentration...

 

[shazzam]

umm, to quote myself...

ehh, nice try but answer is [CF4] = [CO2]=0.16mol/L

this is question 7 on pp226 of Thickett's Chemistry Pathways 2 ,2000 Edition

the other question is q8, so if you wanna take another stab at it...

but, how did you get your concentrations? it's a pity tht your table didn't show up. I mean you are probably right, but...eh basically does your answer math with answer given at back of book?

 

[mervvyn]

oops... sorry bout the stupid mistakes, lucky we have someone to fix it up. i think i need to do a bit more before my trials...

 

[xiao1985]

hoep this helps... ignore the first line abt p/rt = n/v... but the rest is quite self explanatory...

and also, soz abt the ink goin out bit... @@ my pens are dead =(

 

[shazzam]

eeh, this is soooo confusing, hey do you own a copy of conquering chemistry?
preferably the new edition? there's another question