Le Chatelier's principle with Fe3+

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In summary: The third latex code is just like the first, but with x replaced by SCN0. So it looks like this: \frac{x}{(SCN_0)}=\frac{Q(Fe3_0)}{Q(Fe3_0)+1}
  • #1
alingy1
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"The Beer-Lambert relationship must be solved using a FeSCN2+ standard solution. This standard solution can be prepared by mixing a SCN- solution that has a very low concentration with a Fe3+ solution that has avery high concentration. In this situation, the reaction is driven to completion instead of equilibrium, according to Le Châtelier [...]. "

I do not see how Le Châtelier applies here. Q=[FeSCN2+]/([SCN-][Fe3+]) How does having a low and a very high concentration help...
 
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  • #2
The equilibrium still applies, but, since the SCN is mixed with an overabundance of Fe3, virtually all the SCN gets consumed. So the number of moles of FeSCN2 in the final solution is virtually identical to the number of moles of SCN that was present in the original SCN solution.

Chet
 
  • #3
I am not able to picture myself this with calculations. In my head, when we calculate Q, the bottom part becomes a normal value (product of big value with small value)...
 
  • #4
alingy1 said:
I am not able to picture myself this with calculations. In my head, when we calculate Q, the bottom part becomes a normal value (product of big value with small value)...
Q is not calculated. Q is the equilibrium constant.

Let SCN0 be the initial concentration of SCN in the mixture and Fe30 be the initial concentration of Fe3 in the mixture. Let x be the number of moles per liter of SCN that react with Fe3 to produce x moles /liter of FeSCN2. Then:

[tex]\frac{x}{(SCN_0-x)(Fe3_0-x)}=Q[/tex]
Since Fe30 is going to be much greater than SCN_0, we can neglect x compared to Fe30. So the above equation becomes:
[tex]\frac{x}{(SCN_0-x)}=Q(Fe3_0)[/tex]
So,
[tex]\frac{x}{(SCN_0)}=\frac{Q(Fe3_0)}{Q(Fe3_0)+1}[/tex]
So, if Fe3_0 is high enough such that Q(Fe30)>>1,

x -->SCN0

This is the final concentration of FeSCN2 in the solution.
 
  • #5
Wow, this is really clear! Thank you. One small question though. What is the algebra behind your third latex code and your second latex code. I do not understand how you got rid of the -x and divided the left side by Q(Fe30)+1.
*gulp* Sorry, my math is really weak. I admit it. EDIT: IT'S FINE. I COULD FIND IT! :)
 

What is Le Chatelier's principle with Fe3+?

Le Chatelier's principle states that when a system in equilibrium is subjected to a change, the system will adjust itself in order to counteract the effect of the change and maintain equilibrium. In the case of Fe3+, this principle applies to chemical reactions involving iron (III) ions.

How does Le Chatelier's principle apply to Fe3+?

Fe3+ ions can shift the equilibrium of a chemical reaction by either accepting or donating electrons. This can affect the overall concentration of reactants and products, and therefore alter the direction of the reaction according to Le Chatelier's principle.

What factors can affect the equilibrium involving Fe3+?

The concentration of Fe3+ ions, temperature, and pressure can all affect the equilibrium of a reaction involving Fe3+. Changes in any of these factors can shift the equilibrium and cause the reaction to proceed in a different direction.

How can Le Chatelier's principle be used to predict the direction of a reaction involving Fe3+?

By understanding how changes in concentration, temperature, and pressure can affect the equilibrium of a reaction involving Fe3+, we can use Le Chatelier's principle to predict the direction in which the reaction will proceed. For example, if the concentration of Fe3+ ions increases, the reaction will shift towards the side with fewer Fe3+ ions in order to maintain equilibrium.

Can Le Chatelier's principle be applied to all reactions involving Fe3+?

Yes, Le Chatelier's principle can be applied to any reaction involving Fe3+ ions. However, the magnitude of the effect on the equilibrium may vary depending on the specific reaction and the concentrations of the reactants and products.

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