Question

Hydrogen iodide reacts with itself to give hydrogen and iodine. The equilibrium constant is about
2.0 x 10─3 at a particular temperature. If you were to place some hydrogen iodide in a container and
seal the container, what would you expect to find at equilibrium: mostly hydrogen iodide or mostly
hydrogen and iodine?

Answer 1

2HI ==> H2 + I2

K = 2E-3 = (H2)(I2)/(HI)^2
You look at K. With a small number you know the numerator must be small and the denominator must be large. That's the only way you can have a value less than 1. Therefore, you know that H2 and I2 must be small and HI must be large (relatively speaking). So HI must predominate.