Hey Guys, I'm having a really hard time with this one.

Consider the reaction H2(g) + I2(g) ---> 2HI(g). Starting with a concentration of 0.040 M HI, calculate the concentrations of HI, H2, and I2 at equilibrium. The Kc for the reaction is 54.3.

2HI ----> H2 + I2

0.040 M 0 0

-x +x +x

0.040 -x x x

Kc = [H2][I2] / [HI]^2

54.3 = x^2 / (0.040 - x)^2

7.37 = x / (0.040 - x)

0.2948 - 7.37x = x

x = 3.5 x 10^-2

[HI]0.040 - 2 x (3.5 x 10^-2) = 0.03

[H2] = 3.5 x 10^-2

[I2] = 3.5 x 10^-2

I have no idea where I'm going wrong. The answers in the book are: [HI] = 0.031 M [H2] = 4.3 x 10^-3 [I2] = 4.3 x 10^-3

Can somebody please help me out with this one?