5I.3 book problem

[305797394]

In a gas-phase equilibrium mixture of H2, I2, and HI at 500. K, (HI)=2.21×10−3 mol⋅L−1and [I2]=1.46×10−3 mol⋅L−1.Given the value of the equilibrium constant in Table 5G.2, calculate the equilibrium molar concentration of H2.
Does anyone know how to solve this? When I used the quadratic equation to solve it, it came up as undefined so im not sure what im doing wrong.

[Martha Tuna 1K]

Hi,

I was having trouble with this problem too until I realized that the chemical equation was not balanced. H2 + I2 --> 2HI. To find the concentration of H2, your set up must be Kc = [HI]^2 / [H2][I2]. My mistake was not squaring the [HI] to account for the coefficient.

Hope this helps!

[305797394]

hey, i balanced the equation too and i still cant seem to get the right answer. did you use k=160?

[Sally_Luo_3F]

For this question I used K=160 and set up the equilibrium constant equation.
K=[HI]^2/[I2][H2]
160=[2.21*10^-3]^2/[1.46*10^-3]x

you would have to solve for x to get the molar concentration of H2

[305797394]

would i not need to add the "+2x" and "-x" to the HI and I2?