Question

The equilibrium constant Kc for the reaction below is 0.00967 at a certain temperature.

Br2(g) ⇌ 2Br(g)

If the initial concentrations are [Br2] = 0.0427 M and [Br] = 0.0554 M, calculate the concentrations of these species at equilibrium.

Answer 1

.........Br2(g) ⇌   2Br(g)

initial ...0.0427.....0.0554

at eq. (0.0427-x)...(0.0554 + x)

Kc = [Br]^2/[Br2]

given Kc is 0.00967

0.00967 = (0.0554 + x)^2 / (0.0427-x)

0.000413 - 0.00967x = (0.0554 + x)^2

0.000413 - 0.00967x = 0.00306916 +x^2 + 0.1108x

X^2 + 0.12047x + 0.00265616 = 0

X = -0.02905

at equilibrium

[Br2] = 0.0427 -x = 0.0427 -(-0.02905)

         = 0.0717 M

[Br2] = 0.0554 + x = 0.0554 - 0.0290 = 0.0264

Kc