2012 Final #6B

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Shirley Wong 2E
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Joined: Fri Sep 25, 2015 3:00 am

2012 Final #6B

Postby Shirley Wong 2E » Thu Dec 03, 2015 10:52 pm

The question is: The equilibrium constant, Kc, equals 0,045 at 250C for the decomposition reaction: PCl5 (g) <=> PCl3 (g) + Cl2 (g). Calculate the percentage of PCl5 that dissociates if 0.05 mole of PCl5 is placed in a closed vessel (constant volume) at 250C and 2.00 atm pressure.

In the solutions, the Kc=(x/1.072)^2/((0.05-x)/1.072)). Why don't we just find molarity by dividing 0.05 mol PCl5 with the volume we found and then put that into the ICE chart? Why do we have to divide all the concentrations at equilibrium with the volume in the Kc?

Suraj Palaparty 2F
Posts: 27
Joined: Fri Sep 25, 2015 3:00 am

Re: 2012 Final #6B

Postby Suraj Palaparty 2F » Fri Dec 04, 2015 12:48 am

I believe that the volume was 1.072L, so that is essentially what they were doing. In the answers it was just all left in there in order to not break up the (0.05-x).

Posts: 35
Joined: Wed Sep 21, 2016 2:58 pm

Re: 2012 Final #6B

Postby Skolli20 » Sat Dec 03, 2016 12:12 am

When you do it with the ICE chart, you get 61% but it's off by the decimals... is there a reason for this? Or is doing it with an ICE chart a correct way of doing it?

Fengting Liang 1F
Posts: 23
Joined: Sat Jul 09, 2016 3:00 am

Re: 2012 Final #6B

Postby Fengting Liang 1F » Sat Dec 03, 2016 8:24 pm

Can someone explain how he goes from Kc=(x/1.072)^2/((0.05-x)/1.072)) and gets x=0.03059? I keep getting x=0.049 when I plug in Kc...

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