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July 11, 2026, 04:47:01 am

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Toothpaste

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Sample exam 2008 question
« on: October 20, 2008, 08:26:54 pm »
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Page 15 [b]question 3ci[/b]

"increase in volume" - deeper green or lighter green.

cea answers say : lighter
kilbaha says: darker

I put the latter.

Wizard

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Re: Sample exam 2008 question
« Reply #1 on: October 20, 2008, 08:38:36 pm »
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If you increase the volume, you are actually decreasing the pressure. The system will attempt to offset this change by increasing the pressure of the system. It does this by going to the side which has more gaseous atoms. Looking at the equation, the forward reaction is favoured, and the equilibrium shifts to the right. Therefore, You will get a higher yield of chlorine than you started with, so I would say darker :) (as the chlorine is green)

Collin Li

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Re: Sample exam 2008 question
« Reply #2 on: October 20, 2008, 08:42:05 pm »
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An increase in volume initially lowers the concentration. Le Chatelier's principle states that the change will only be partially offset, which means the final equilibrium concentration will still be lower than the initial equilibrium concentration (despite Le Chatelier's principle working to increase the concentration from the disequilibrium). The answer is in fact: lighter.

Mao

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Re: Sample exam 2008 question
« Reply #3 on: October 20, 2008, 08:44:32 pm »
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lighter.

remember that LCP only partially oppose a change [this is always true, there was a thread on this a while ago when coblin proved this]

hence, increase in volume is a decrease in concentration (colour is lighter)
and the subsequent shift to the right (more green) only partially opposes this, and overall the colour is still lighter.
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Toothpaste

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Re: Sample exam 2008 question
« Reply #4 on: October 20, 2008, 08:46:19 pm »
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An increase in volume initially lowers the concentration. Le Chatelier's principle states that the change will only be partially offset, which means the final equilibrium concentration will still be lower than the initial equilibrium concentration (despite Le Chatelier's principle working to increase the concentration from the disequilibrium). The answer is in fact: lighter.

oh shit.

thanks

like the resulting change in the attached picture doesn't go back to the way it was (maroon line) yeah?

ice_blockie

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Re: Sample exam 2008 question
« Reply #5 on: October 20, 2008, 08:48:31 pm »
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Quote
like the resulting change in the attached picture doesn't go back to the way it was (maroon line) yeah?

Yes, the concentration of chlorine gas never returns to its original concentration.

Toothpaste

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Re: Sample exam 2008 question
« Reply #6 on: October 20, 2008, 08:50:04 pm »
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Quote
like the resulting change in the attached picture doesn't go back to the way it was (maroon line) yeah?

Yes, the concentration of chlorine gas never returns to its original concentration.
etched into mind now :)

yay for mistakes and learning.

Wizard

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Re: Sample exam 2008 question
« Reply #7 on: October 20, 2008, 08:50:28 pm »
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Sorry, I overlooked that it returns to less than its original concentration, so it is lighter! Tricky :)

ice_blockie

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Re: Sample exam 2008 question
« Reply #8 on: October 20, 2008, 08:56:27 pm »
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anyway, i would have assumed cea was right as those answers have been around for a while now...

shinny

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Re: Sample exam 2008 question
« Reply #9 on: October 20, 2008, 08:59:38 pm »
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In addition to the fact that kilbaha is KILBAHA.
MBBS (hons) - Monash University

YR11 '07: Biology 49
YR12 '08: Chemistry 47; Spesh 41; Methods 49; Business Management 50; English 43

ENTER: 99.70


Toothpaste

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Re: Sample exam 2008 question
« Reply #10 on: October 20, 2008, 09:00:28 pm »
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I lack -risk assessment- haha

Collin Li

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Re: Sample exam 2008 question
« Reply #11 on: October 20, 2008, 09:24:24 pm »
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I don't remember doing this proof Mao, but I do remember using a really cumbersome method to prove some acidity constant question. (Then finding an elegant method ;D)

But yes, using the theory of equilibrium, we can prove this with mathematics (which you don't need to do or know for VCE Chemistry!):



Take a reaction: with

Suppose that the initial concentrations (at equilibrium) are: , , and , where .



Now, half the volume so that every concentration is doubled. Now,

The system is now thrown into dis-equilibrum, and must decrease in order to return to .

Thus, and must decrease and must increase (via the backward reaction of the chemical equation above).

Following the reaction, the system will re-establish the equilibrium as follows:

,

,

,

where



Since :



          (***)





Since :









Similar working from line (***) can be done to conclude as well.



This proves that the final equilibrium and is greater than the initial equilibrium and , despite the principles of equilibrium working to reduce both and from and respectively.
« Last Edit: October 20, 2008, 10:49:45 pm by coblin »

onlyfknhuman

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Re: Sample exam 2008 question
« Reply #12 on: November 01, 2008, 08:56:15 pm »
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coblin your FKN genius wat the holly
English - VCD - Methods - Physics - Chemistry - Art - Japanese

give me the name list of all the hot chicks u know  ;)

Collin Li

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Re: Sample exam 2008 question
« Reply #13 on: November 01, 2008, 11:22:36 pm »
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:D

I'm only fkn human too! SO YOU CAN DO IT TOO (after VCE exams are over, since this is irrelevant)!