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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tabularasa on September 24, 2008, 06:34:47 PM

Title: Equilibrium Concentrations
Post by: tabularasa on September 24, 2008, 06:34:47 PM

On my practice quiz, this is my question: Consider the following reaction, equilibrium concentrations, and equilibrium constatn at a particular temperature. Determine the equilibrium concentration of CO2(g).

NH2COONH4(s) <--> 2NH3(g) + CO2(g)

Kc = 1.58 x 10^-8

[NH3]eq = 2.9 x 10^-3 M

I know an ICE table is supposed to be used, but how can I find the initial concentrations of all 3 species and find the other two equilibrium concentrations?  Or am I making this more complicated than it has to be?

Title: Re: Equilibrium Concentrations
Post by: enahs on September 24, 2008, 08:07:30 PM

ICE is not required.

If you were given this reaction and asked to write the equilibrium constant expression for it, what would it look like?
What do we give solids in the equilibrium constant?

Now that you have done all that, and you are given the constant, you have one equation and one unknown, solve for your concentration of CO2.

Title: Re: Equilibrium Concentrations
Post by: tabularasa on September 24, 2008, 10:02:31 PM

Solids are not expressed in the expression!

I was overthinking it. Thank you for your help, I got the right answer!

Title: Re: Equilibrium Concentrations
Post by: enahs on September 24, 2008, 10:07:02 PM

Well, they are expressed as 1 (which is a simplification). But anything *1 or /1 is still the same thing.