Posted by Dan on Saturday, November 3, 2007 at 6:15pm.
A container initially has 0.0186 M ammonia at a certain temperature. When the system reaches equilibrium the concentration of ammonia is 0.0035 M. Calculate Kc for the following reaction as written.
N2(g) + 3H2(g) > 2NH3(g)

Chemistry  DrBob222, Saturday, November 3, 2007 at 6:26pm
Write the Kc expression from the equation..
N2 + H2 ==> 2NH3
Then 0.0186 M NH3 initially.
At equilibrium H2 must be 3x, N2 must be 2x, and NH3 must be 0.01862x. Plug those values in and solve for Kc. 
Chemistry  Dan, Saturday, November 3, 2007 at 6:58pm
Thanks, that's what I got :)