Equilibrium Question

[HarveyD]

We are given this reaction:
Fe3+ + SCN- ----> Fe(SCN)

1) If NaF is added, which reactant would it react with? Would it be right to say that if it was with SCN- then the concentration of SCN would initially decrease. Then a net back backward reaction would occur?

2) If an equal amount of water was added (dilution), what would be the effect? Would it just be a net back reaction? Or would I have to say more? My teacher was saying that there wasn't in fact a net shift since they're diluted proportionally to one another...is that right/something I should include?

[jane1234]

1) Yes, the backward reaction would increase because the system is trying to compensate for the lost SCN- ions which were removed when they reacted with the NaF. Initially the concentration of the Fe(SCN) would decrease in order to increase the concentration of SCN- ions to restore equilibrium.

2) Not too sure on this, but I think your teacher is right in that there won't be a net change in that the water will be interacting with both the reactants and the product. There may be a small change, but I think this is negligible so I wouldn't worry about it. Might want to double check though.

[Greatness]

We just did a prac that involved this stuff
1) The F- ions react with the Fe3+, so there will be a decrease in the amount of Fe3+. Hence a net back reaction will occur to compensate for that change.
2) When you dilute a solution, the reactoin goes towards the side which has a greater no. of particles. So it will be a back reaction. The concentrations of everything decreases as well i think - but the no. of particles remains the same.

[HarveyD]

can i just confirm the answer for 2
is there a net shift? :S

[HarveyD]

bump :S
sorry this is urgent
got a sac on friday D:

[Greatness]

Ok so im looking at A+ notes, it says specifically for this reaction: 'there is a net shift to the left, i.e. the colour lightens if:
-the solution is diluted. herre the system adjusts iteslf to the left to produce more particles to make up for the dilution.
NOTE: take care with dilution. in the net shift to the left the concentration of Fe(III) and the thiocyanate ion both decrease but the actual no. of moles increases'
This is probably a very reliable answer

[HarveyD]

alright thanks heaps
easier to explain than the no shift as well xD

hmm can you explain the no. of moles things?
thought it would stay the same since nothings being added/taken away

nvm

[HarveyD]

ohh btw
with the addition of AgNO3 and NaF
would both Fe and SCN react with one of ions, i.e FeNO3 and AgSCN or NaSN or FeF
or just one? :S
if so which one would it be D:

[Vincezor]

ohh btw
with the addition of AgNO3 and NaF
would both Fe and SCN react with one of ions, i.e FeNO3 and AgSCN or NaSN or FeF
or just one? :S
if so which one would it be D:

Addition of NaF decreases the amount of Fe3+ because F- ions react with Fe3+ ions to form

Addition of AgNO3 decreases the amount of SCN- because Ag+ ions react with SCN- ions to form a white preciptitate of AgSCN

[HarveyD]

thanks for that

just wondering if any of guys would be able to check my explanation for what happens when more reactant is added to a system in equilibrium (my teacher says we need to be concise and specific rather than writing essays so i really want to get it right for the SAC tomorrow)

According to Le Chatelier's principle the system will move to oppose this change caused by the addition of reactant. Hence as it re-adjusts to this change, it will consume the extra reactant, creating more products and hence undergoing a net forward reaction. By doing so, it will be able to re-establish equilibrium once more. (And then I will link this to the colour change we saw)

Does that sound alright?

[jasoN-]

According to Le Chatelier's principle the system will move to oppose this change caused by the addition of reactant. Hence as it re-adjusts to this change, it will by consuming the extra reactant, creating more products and hence undergoing a net forward reaction. By doing so, it will be able to re-establish equilibrium once more.

IMO answer is too long, unnecessary words added for minimal/no benefit, although I doubt you'll be marked down for doing this

According to Le Chatelier's principle the system will oppose this change caused by the addition of reactant. It re-adjusts to this change, by consuming the extra reactant, creating more products and hence undergoing a net forward reaction. By doing so, it will re-establish equilibrium once more.

[thatricksta]

For the record, this information can actually be found in your chemistry "work book"... I assume most people don't like it, but it does have some useful information so don't feel like its a useless source of info