Question

A mixture initially contains A, B, and C in the following concentrations: [A] = 0.500 M , [B] = 1.20 M , and [C] = 0.700 M .

The following reaction occurs and equilibrium is established: A+2B⇌C At equilibrium, [A] = 0.390 M and [C] = 0.810 M . Calculate the value of the equilibrium constant, Kc.

Answer 1

A      +     2B   <----> C
0.500      1.20            0.700   (Initial)
0.500-x   1.20-2x     0.700+x (at equilibrium)

given,
[C] = 0.700+x
0.810 = 0.700 + x
x = 0.110 M

So,
[B] = 1.20 - 2x = 1.20 - 2*0.110 = 0.980 M

Kc = [C] / {[B]^2 [A]}
Kc = 0.810 / (0.980^2 * 0.390)
Kc = 2.16

Answer: 2.16