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### Topic: Utilizing Le Chatelier's Principle to calculate the equilibrium constant  (Read 6570 times)

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#### tiny101

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• Mole Snacks: +0/-1 ##### Utilizing Le Chatelier's Principle to calculate the equilibrium constant
« on: May 28, 2008, 02:02:52 AM »
Find the equilibrium constant Kc for O2 (g) + O(g)

#### cliverlong

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• Mole Snacks: +60/-14 ##### Re: Utilizing Le Chatelier's Principle to calculate the equilibrium constant
« Reply #1 on: May 28, 2008, 02:54:02 AM »
Hi

If you want to calculate a value, I believe you need

1. a chemical equation
2. some concentrations or partial pressures of reactant and products at equilibrium

If you just want a value for Kc then there might be tables to look that up.

On the idea of "Utilizing Le Chatelier's Principle to calculate the equilibrium constant" the following thread (lower down)

http://www.chemicalforums.com/index.php?topic=26589.0

courtesy of Borek ,suggests the "idea" should be the other way round to what you have stated, Le Chat is a simplification of the equation for Kc

#### tiny101

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• Mole Snacks: +0/-1 ##### Re: Utilizing Le Chatelier's Principle to calculate the equilibrium constant
« Reply #2 on: May 28, 2008, 10:39:20 PM »
Sorry, there was something wrong with the original post - the question I cut & paste did not appear. Here is the question in full, I hope.

Find the equilibrium constant KC for O2 (g) + O(g) -> O3 (g) given that NO2 (g) -> NO(g) + O(g) has KC = 6.8E-49 mol/L and O3 (g) + NO(g) -> NO2 (g) + O2 (g) has KC = 5.8E-34. If the overall reaction is initially at equilibrium with [O2 (0)] = 8 mol m−3 and [O3 (0)] = 1.25 mol m−3, and .25 mol m−3 of O3 is added at constant temperature, what are the new final concentrations of O3 , O2 and O? Are these in accord with Le Chatelier’s principle?

*NOTE: All the arrows -> mean that the reaction can proceed forward or backwards... I just don't know how to do a double-headed arrow.

#### Astrokel

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« Reply #3 on: May 28, 2008, 11:11:22 PM »
hey!

Write out the Kc expression for the 3 reversible reactions and do you see something?

Part 2: Draw up an ICE table!

You don't have to use qualitative explanation using Le Chatelier's principle here, but indirectly, you are using it in the ICE table.

Try it out No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

#### tiny101

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• Mole Snacks: +0/-1 ##### Re: Utilizing Le Chatelier's Principle to calculate the equilibrium constant
« Reply #4 on: May 29, 2008, 12:13:29 AM »
I just tried using ICE tables, but there are so many unknowns. How should I apply ICE tables to the NO2 -> NO + O and O3 + NO -> NO2 + O2 equations when I do not know any of the concentration information?

Thanks again =)

#### Astrokel

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« Reply #5 on: May 29, 2008, 12:44:02 AM »
hey,

O2 (g) + O(g) <---> O3 (g)

Use this reaction. The other two reactions are in the question because you do need them to find the Kc value of the above reaction in part 1.
No matters what results are waiting for us, it's nothing but the DESTINY!!!!!!!!!!!!

#### cliverlong

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• Mole Snacks: +60/-14 ##### Re: Utilizing Le Chatelier's Principle to calculate the equilibrium constant
« Reply #6 on: May 29, 2008, 05:12:54 PM »
Sorry, there was something wrong with the original post - the question I cut & paste did not appear. Here is the question in full, I hope.

Find the equilibrium constant KC for O2 (g) + O(g) -> O3 (g) given that NO2 (g) -> NO(g) + O(g) has KC = 6.8E-49 mol/L and O3 (g) + NO(g) -> NO2 (g) + O2 (g) has KC = 5.8E-34. If the overall reaction is initially at equilibrium with [O2 (0)] = 8 mol m−3 and [O3 (0)] = 1.25 mol m−3, and .25 mol m−3 of O3 is added at constant temperature, what are the new final concentrations of O3 , O2 and O? Are these in accord with Le Chatelier’s principle?

*NOTE: All the arrows -> mean that the reaction can proceed forward or backwards... I just don't know how to do a double-headed arrow.
I find it difficult to follow your question because of the layout. I think a solution may be clearer if you adopt the following layout and write the equations in the following order

NO2 <-> NO + O   Kc1 = . some expression using the data you have ...

O2 + O <-> O3    Kc2 = . some expression using the data you have ...

NO + O3 <-> NO2 + O2    Kc3 = . some expression using the data you have ...

Then build an ICE table for each and start by saying at equlibrium the change in equation 1 is due to a loss of "x" amount of NO2. What does equation 1 give you by applying ICE as suggested above?

Then do the same for  equation 2 but try to link it to the change in equation 1.

Then do the same for  equation 3 but try to link it to the change in equation 1 (and 2?).

Now you should have equations in "x". Try and eliminate things and find "x". I haven't actually waded through this but it might work (no guarantees express or implied ... )

Interesting that you are given concentrations to work with when all the reactants are in the gas phase. I thought Kp is more appropriate in such a situation but I guess concentrations and Kc will work ...

Clive