Unit 4 Questions MEGATHREAD!

[Christiano]

Yeah I did, I'm just having a problem solving the equation algebraically. I can solve it on my CAS using 'solve', but rearranging the equation isn't working..

1.75 x 10^-5 = (2.24 x 10^-4)^2 / [ethanoic acid]

Simple I know ... but I can't wrap my head around it xD

[Graphite]

1.75 x 10^-5 = (2.24 x 10^-4)^2 / [ethanoic acid]
1.75 x 10^-5 x [ethanoic acid]= (2.24 x 10^-4)^2
[ethanoic acid]=(2.24 x 10^-4)^2 /1.75 x 10^-5

[vea]

Can an increase in pressure change the value of K? From what I've learnt, nothing can change the value of K except for temperature changes but TSSM 2008 exam says otherwise :S

[Graphite]

Remember it can change the K but not the Keq

[vea]

Remember it can change the K but not the Keq

Yeah, the concentration fraction will change but it will eventually re-establish equilibrium with the same equilibrium constant. Probably just ambiguity in the definition of 'K' and such...

[luken93]

Hence why you use Q, the Equilibrium Quotient. It's just easier to do these sorts of things, saves you from getting mixed up!

[nacho]

everytime i see this thread, i realise i havent touched chemistry in 2 months.
How can i most effectively study for this subject, given that it bores the crap out of me?

[vea]

The molar volumes of an ideal gas at STP (22.4L/mol) and SLC (24.5L/mol) are not 100% accurate but from suggested solutions of prac exams and stuff, seem to be the more acceptable way of calculating gas related things. Would we actually be penalised if we followed the general gas formula and did

101.325xV=n x 8.31 x 273 (or 298) instead? 

Thanks

EDIT: Inaccurate as in the solutions are sometimes a few digits out of place, don't want to lose SF marks and such now!

[david10d]

For the people using the Heinemann book, how much of chapters 18, 23 and 24 do we have to know? My school is using the Nelson book and we've only covered the 11 industrial steps (w/e they're called).

also

have you guys started exams? the unit 4 checkpoints seems really dodgy and i think i should move away from it lol

[HarveyD]

CH3COOH(aq)+ NaHCO3 (s) ----> NaCH3COO(aq)+ CO2 (g) + H2O(l)
Which of the following properties could best be used to measure the reaction rate?
A. the volume of CO2
B. the volume of H2O
C. the mass of CH3COOH
D. the surface area of NaHCO3

[b^3]

Either A or C, but I am leaning towards Ok lets say C.
A. the volume of CO2
Since the rate that CO² is being produced is proptional to the rate of the reaction, if you use say a syringe to collect the gas, then plot the volume of gas against time, then the gradient will give the rate of reaction. But this is proabably 'less best' (if that makes sense) because the volume of gas will change with pressure that is applied by the syringe.

C. the mass of CH3COOH
As the mass decreases, if you plot the graph of the mass against time, the gradient will give the rate of reaction. Basically you have the beaker/flask placed on a set of scales and record the weight at regular time intervals as the reaction occurs.

Just so I know what was the answer?

The unit 4 checkpoints seems really dodgy and i think i should move away from it lol

Checkpoints wasn't that bad and it can be done in just over a week, but then I have expirenced the horror of methods checkpoints.

EDIT: Post number 666

[HarveyD]

answer is D lol :/
anything wrong if you put A or C?

[b^3]

Quick question, how the hell are we supposed to measure the surface area of a solid while it is undergoing a reaction? I still think C is correct and works, what does everyone else think?

[HarveyD]

i have a feeling its a typo and they meant to ask how to increase the rate?
maybe..

[b^3]

Yeh that makes sense, lets hope so.