Use K and initial concentrations to calculate equilibrium concentrations

Question

Consider the equilibrium system involving the decomposition of hydrogen iodide.

2HI(g) H2(g) + I2(g)	K =	[H2] [I2]	= 2.68×10-2 at 1140 K
[HI]2

A flask originally contains 0.247 M hydrogen iodide. Calculate the equilibrium concentrations of the three gases.

[HI]	=
[H2]	=
[I2]	=

Answer 1

Set up an ICE table:

2HI(g) <===> H₂(g) + I₂(g)

0.247...............0.............0..........Initial

-2x..................+x...........+x.........Change

0.247-2x..........x.............x..........Equilibrium

K = [H₂][I₂] / [HI]²

2.68x10^-2 = (x)(x) / (0.247-2x)²

Use the quadratic formula to solve for x

When you find the value of x, go back to the equilibrium line of the ICE table and plug in x and solve for the concentrations of each gas.