Question

The equilibrium constant Kc for the reaction

C <--> D + E

is 7.90 * 10^-5. The initial composition of the reaction mixture is [C]=[D]=[E]=1.10*10^-3. What is the equilibrium concentrations of C, D, and E?

C=?
D=?
E=?

Answer 1

K = 7.9E-5 = (D)(E)/(C)
Qc = (0.0011)(0.0011)/(0.0011) = 0.0011
Qc > Kc; therefore, products are too large and reactants too small. The reaction most go to the left to reach equilibrium.

..........C ==> D ...+... E
I......0.0011..0.0011..0.0011
C.........x.....-x.......-x
E...0.0011+x..0.0011-x.0.0011-x

Substitute the equilibrium line from the ICE chart into Kc expression and solve for x, then 0.0011+x and 0.0011-x.