How does the value of an equilibrium constant relate to the relative quantities of reactants and products at equilibrium?

Question

matt101 · Answer

Look at how the equilibrium constant is calculated. In general:

$$K={[P] \over [R]}$$
Concentration of products over concentration of reactants.

If K is a very big number, the NUMERATOR on the other side must be much larger than the DENOMINATOR. The numerator is the product concentration, so for a big K, the products must be favoured at equilibrium.

On the other hand, If K is a very small number, the DENOMINATOR on the other side must be much larger than the NUMERATOR. The denominator is the reactant concentration, so for a small K, the reactants must be favoured at equilibrium.