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?
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.
To determine whether the equilibrium mixture will mostly contain hydrogen iodide or mostly hydrogen and iodine, we can use the equilibrium constant (K).
In this case, the equilibrium constant is 2.0 x 10─3.
If the equilibrium constant (K) is less than 1, it means that the reactants are favored at equilibrium. On the other hand, if K is greater than 1, it means the products are favored at equilibrium.
In this case, the equilibrium constant (K) is very small (less than 1), which indicates that the reactants (hydrogen iodide) are favored at equilibrium. Hence, we would expect to find mostly hydrogen iodide in the container at equilibrium.
To determine what would be present at equilibrium (mostly hydrogen iodide or mostly hydrogen and iodine), we need to compare the value of the equilibrium constant (K) with the initial concentrations of the reactants.
In this case, the equilibrium constant is given as 2.0 x 10⁻³. This value indicates that the reaction favors the products (hydrogen and iodine) over the reactant (hydrogen iodide).
If the initial concentration of hydrogen iodide is relatively high, there will be a higher concentration of hydrogen and iodine at equilibrium. On the other hand, if the initial concentration of hydrogen iodide is relatively low, there will be a higher concentration of hydrogen iodide at equilibrium.
So, based on the equilibrium constant and the reaction favoring the products, we can expect that at equilibrium, there will be mostly hydrogen and iodine present rather than mostly hydrogen iodide.