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AR15.COM
3/11/2007 6:43:11 PM EDT
In an experiment, 0.100 mol H2 and 0.100 mol I2 are mixed in a 1.00 liter container and the reaction forms HI. If Kc = 0.0200 for the reaction,
2HI(g) ->  I2(g) + H2(g)
what is the equilibrium concentration of HI?
A.0.200 M         C. 0.156 M
B.0.0780 M D. 0.0384 M

I know the answer is C (I solved it earlier) but I can't remember how I did it. I have spent an hour on this damn thing already.

It has to do with this formula:

Kc= (conc. of products^exponent)/(conc. of reactants^exponent)

So, it could look like this:

Kc=.02=((HI)^2)/(.1*.1)

OR, the numbers could go into the "delta molarity"chart to get a quadratic eqn.

This is the quadratic I get from it:

.0002 -.0004X - .98X^2 = 0

PLEASE SHARE YOUR WISDOM!