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# Equilibrium Constant Question watch

1. Hello everyone. I'm currently doing some revision for the Edexcel Unit 4 exam on Wednesday, but it's proving rather difficult to practice the numerical stuff seeing as the textbook provides questions, but no answers.

"The reaction CH3COOC2H5(l) +H2O(l) <-> CH3COOH(l) + C2H5OH(l) has a Kc value pf 0.25. 0.2 moles of CH3COOC2H5 is mixed with 0.6 moles of water in a stoppered bottle. The mixture is kept at 323K until equilibrium is reached. How many moles of ethanoic acid will be in the equilibrium mixture?"

I got 0.107 moles (3s.f.). Would anyone mind checking that for me please? I'd be really grateful.

(Or if anyone just happens to have a gigantic list of answers for the new Edexcel A2 book, that would also be incredible!!)
2. I'm getting 0.173 ??
3. Oh, well I'm glad I checked it here then!!

Did you form a quadratic, 0.75x^2+0.2x-0.03=0, or equivalent?

4. Or am I talking out of my arse?
5. Yup, that's what I got.

I said, at equlibrium, there are (0.2-x) moles of the ester, (0.6-x) of water, x of the acid, and x of the alcohol.

So 0.25=(x^2)/((0.2-x)(0.6-x))?
6. Ah yes indeed you are correct.

Solve using formula.

=0.107 mol
7. Awesome, thanks. That's reassuring.
8. (Original post by StandardCarpet)
Awesome, thanks. That's reassuring.
No worries. Sorry for the ******** answer to begin with and taking ages to reply. Good luck with your exam.

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Updated: January 25, 2010
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