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liv · « **on:** August 01, 2010, 04:46:16 pm »

well
for Fe3+(aq) + SCN-(aq) <--> Fe(SCN)-(aq)

if you add Fe(NO3)3, then it increases the concentration of the Fe3+ so the system goes in the forward direction to oppose the change, right?

if i have a question that asks 'use le chatelier's principle to account for the way in which the position of eqilibrium shifts in this test', is that asking me to explain that the reaction goes forward, or something else...?

i am so confused. and tired. and exam results come out tomorrow. *sigh*

+ karma for a good answer.

98.40_for_sure · « **Reply #1 on:** August 01, 2010, 04:53:21 pm »

Adding Fe(NO3)3 is addition of reactants thus a net forward reaction to oppose the up in concentration (thus down, by turning it into products). Basically if it asks you to use le chatelier's principles, mention the buzzwords, such as "partially oppose" "net forward".

You might want to explain that although it is a net forward reaction, the concentration of Fe3+ overall increases, as the net forward reaction cannot fully compensate for the physical change of increasing Fe3+ initially. As Fe(SCN)- is a red colour, and reactants are colourless and pale yellow respectively, you can mention that addition of Fe(NO3)3 causes the colour to darken, a more intense red?

stonecold · « **Reply #2 on:** August 01, 2010, 04:54:53 pm »

^Yep, you are 100% right.

Does every school do this experiment haha?

vexx · « **Reply #3 on:** August 01, 2010, 04:55:02 pm »

Sorry i just realised i read your question weirdly,
Yeah as 99.95 said, adding the Fe(NO3)3 will increase the concentration of Fe3+ and so the system will try and oppose the change by a net forward reaction..

98.40_for_sure · « **Reply #4 on:** August 01, 2010, 04:56:06 pm »

Quote from: stonecold on August 01, 2010, 04:54:53 pm

^Yep, you are 100% right.

Does every school do this experiment haha?

Lol yeah i think so... my teacher even made the sac centred around results from this prac. fill in a huge table about what goes up, what goes down etc

liv · « **Reply #5 on:** August 01, 2010, 05:05:52 pm »

so the reaction goes forward, but does that mean the position of the equilibrium changes? or does that mean the same thing?

98.40_for_sure · « **Reply #6 on:** August 01, 2010, 05:09:11 pm »

Quote from: liv on August 01, 2010, 05:05:52 pm

so the reaction goes forward, but does that mean the position of the equilibrium changes? or does that mean the same thing?

The position of equilibrium shifts (same as net forward reaction), but the value of K, the equilibrium constant does not change.

vexx · « **Reply #7 on:** August 01, 2010, 05:20:25 pm »

Quote from: 99.95_for_sure on August 01, 2010, 05:09:11 pm

Quote from: liv on August 01, 2010, 05:05:52 pm
so the reaction goes forward, but does that mean the position of the equilibrium changes? or does that mean the same thing?

The position of equilibrium shifts (same as net forward reaction), but the value of K, the equilibrium constant does not change.

K remains and only changes with temperature, but since there is a net forward reaction, the 'concentration fraction' increases above the value for K which is similar to the equilibrium constant but it is for a specific point in time where the reaction is not at equilibrium.

liv · « **Reply #8 on:** August 01, 2010, 05:25:06 pm »

OH I SEE

i am now not confused. thanks!

physics · « **Reply #9 on:** August 01, 2010, 08:42:42 pm »

lol this experiment was our sac.

Martoman · « **Reply #10 on:** August 01, 2010, 10:29:49 pm »

Our's too!

Maybe its a morbid fetish amoung chemists or some kind of crude, ridiculously intellectual inside joke we fail to comprehend?

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