A student ran the following reaction in the laboratory at 636 K:

2HI(g) -> H2(g) + I2(g)

When she introduced 0.316 moles of HI(g) into a 1.00 liter container, she found the equilibrium concentration of I2(g) to be 3.12×10-2 M.

Calculate the equilibrium constant, Kc, she obtained for this reaction.

Kc =

Explanation:

1. Calculate the iniital concentration of HI(g) introduced

The initial concentration of HI(g), [HI(g)], is the number of moles per liter:

2. Build the ICE (initial, change, equilibrium) table

ICE table:

          2HI(g)          →        H₂(g)      +       I₂(g)

I          0.316                         0                   0

C         - 2x                         +x                   +x      

E         0.316 - 2x                 x                    x       (x =  3.12×10⁻²M)

3. Find the equilibrium constant, Kc