prac on modelling equilibrium? (1 Viewer)

[fashionista]

hi there!
we tried to do this prac in class but everyone's screwed up somethin severe and we didnt ever find out wut the outcome was supposed to be.
we did this one where you have two measuring cylinders and two different sized pipettes and u transfer water from one cylinder using the larger pipette and then transfer it back to the original cylinder using the smaller one. im pretty sure thats correct anyway.
so we had to do that i think 30 times and we 'should' have noticed something but that was near impossible for me as i was doing a test at the time and my friends didnt get a result and as mentioned above neither did anyone else.
help would be greatly appreciated!!

oh and the prac that asks you to observe the reactions of sulfuric acid acting as an oxidising agent by testing with Mg, Zn and Fe. This one I don't have the results for either.
If anyone has done this experiment, or any experiment relating to this dot point please help me!!!!!!!!!!
I will be eternally grateful!!

 

[ben7]

Theres a great prac written up on modelling equilibrium in 2002 standards package that I am goin to use becasue yeah ours didnt go to flash either.

Ok so the equilibrium is between NO3 and N2O4 was prepared by getting a flask and putting solid copper in it and a solution of HNO3 around it. The has that evolved was collected in the top of the flask and in a syringe that is connected to the cork in the top of the flask.

The great thing about this experiment is the PRESSUE in the equilibium could be change by pushing the syringe in and out. SO the syringe is pushed in and out and the change in colour of the gass was observed (this is qualitative analysis) showing a shift in equilibrium when the pressure changed.

The syringe was placed in cool and hot water to see what temp did to the equilibrium as well.

The equilibrium is 2NO2 ( g ) <----> N2O4 ( g ) with a brown gas for 2NO2 and colourless for N2O4
at high pressure (ie syringe pushed in) the equilibrium shifted to the side with less moles - the N2O4 side which meant the gas became a lighter brown colour as more N2O4 was made. same story with with lower pressures except shifts the other way.

it could be determined whether it was endothermic or exothermic by the gases reaction in warm or cold water. brown gas lightened when in warm water showing the equilibrium reaction is exothermic.

2NO2 ( g ) <----> N2O4 ( g ) + heat

thats about it i think. remember to mention lechateliers principle.

Hope that helps.

 

[beta-omega]

im not sure if thats the same prac, thats a qualitative analysis of an equilibrium, fasionista wated the modelling of an equlibrium reaction, i've got this one that uses microsoft excel to do it , see u can talk about computer aided technologies .

 

[ben7]

oh modelling of an equilibrium... sorry. well for that i use a guy walking up and escillator in fact i am doing a Q on it right now.

 

[fashionista]

no no, what ben7 said is great! THANK YOU SO MUCH!!!!!! this prac is way better than the one we did, thanks so much for it!!! thank u and good luck tomorrow!!!

 

[ben7]

no worries. good luck to u too!

 

[beta-omega]

looks absolutely lost

 

[Plebeian]

im not sure if thats the same prac, thats a qualitative analysis of an equilibrium, fasionista wated the modelling of an equlibrium reaction, i've got this one that uses microsoft excel to do it , see u can talk about computer aided technologies .

I think you're right, can you explain your one a bit further?

 

[charbar]

hey BETA and TECHIE could u both please go to the 'calculating solvay" please and help me out with the question! pelase guys

 

[beta-omega]

ok, i'll scan the sheet and post it up some time soon, but what we did is program excel so that there is one forward and one reverse reaction. THere was also concentrations of the inital reactants, and the initial products. Then all you had to do was type in the rate of the forward and the rate of the reverse reaction, and then allow the reaction to go for like, wot 50 steps. Eventually, your concentration of reactants equal the concentration of products, and stay like that no matter how much more you proceed the reaction, and thus equilibrium.

 

[charbar]

i meant the 'calculating solvay' thread in industrial chem area (btw sorry for interupting)

 

[beta-omega]

heres, the sheet, u can do it for fun

 

[ben7]

OK fashista the thing i wrote up is on quantivly measuring changes in equilibrium not modeling it. I copied this straight out of John Mu's chem summary, all credit to him

identify data, plan and perform a first-hand investigation to model an equilibrium
reaction
A person walking backwards on a escalator could be seen as a equilibrium reaction
When the person walks forward at the same speed as the escalator is moving he/she appears
stationary from a macroscopic perspective
However, his feet which are hidden from view are still moving, thus there are still
microscopic changes
If the escalator speeds up, the person walking will also speed up to minimise the disturbance
But this change will result in him stoping at a different part of the escalator, thus the position
of equilibrium has changed

 

[fashionista]

oh i figured that one out...with the measuring cylinders and pipettes, eventually the amount of water u transfer in a cycle doesnt change the amount in wither cylinder therefore equilibrium is established and this demonstrates that equilibrium can be established from either end..but its bad because it doesnt show a closed system.