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**VexedPig**:

Question 9: Answer BOTH parts (a) and (b).

The Kc at a particular temperature for the following reaction is 1.6x10-6 M.

2NOCl(g) ⇌ 2NO(g) + Cl2(g)

Calculate the concentrations of all the species at equilibrium for the following original mixtures:

a) 3.0 mol pure NOCl in a 3.0 Litre container

b) 2.5 mol NO and 1mol Cl2 in a 1Litre container

**sjb**:

Any thoughts of your own on how to start?

**VexedPig**:

--- Quote from: sjb on May 02, 2019, 02:16:45 AM ---Any thoughts of your own on how to start?

--- End quote ---

Tried doing ICE method a hundred times and get some weird cubic equation at the end of it. I just want someone to acknowledge I'm not going completely insane.

**mjc123**:

Why don't you show your working so we can see whether you're insane or not?

Yes, you do get a cubic equation. But in this case you can use the fact that Kc is very small to predict that the equilibrium is well over to the left. For part a, using the ICE table, I get

Kc = 4x3/(1-2x)2, where x is the equilibrium concentration of Cl2. Is this what you get?

But since K is so small, we can try making the simplification that x << 1, so (1-2x) ≈ 1. Then it's easy to solve, and you can (should) then check whether the assumption x << 1 is true.

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