Solution
Given data
Kc =4.0*10-2
Initial moles of NH3 = 1220
Equilibrium concentration of H2= ?
Lets make the ICE table
   2NH3 ------ > N2 + 3H2
IÂ Â 1220
MÂ Â Â Â Â Â Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â Â Â Â Â Â
CÂ Â
-2x                   Â
+x          Â
+3x
EÂ Â
1220-x             Â
x            Â
3x
Lets write the equilibrium constant expression
Kc =[N2][H2]3/[NH3]2
Now lets out the values in the formula
4.0*10-2 =
[x][3x]3/[1220-2x]2
4.0*10-2
*[1220-2x]2=[x][3x]3
By solving this equation we get
X= 1.16
Therefore the equilibrium concentration of H2 = 3x =
3*1.16 = 3.48 M
