The Equilibrium Constant Expression

The position or extent of a chemical equilibrium can be expressed quantitatively using the equilibrium constant (K_eq).

The equilibrium constant may be written as the following, which is based on the ratio of products to reactants of an equilibrium system at a specific temperature:

K_{\text {eq}} = \frac{ [\text{products}]}{[\text{reactants}] }

But more specifically, it is calculated using the equilibrium constant expression. For the reaction below:

a\text A + b\text B ⇌ c\text C + d\text D

the equilibrium expression is:

K_{\text{eq}} = \frac{[\text C]^c[\text D]^d}{[\text A]^a[\text B]^b}

A change in temperature is the only factor that will cause the equilibrium constant to change. Factors such as pressure, concentration and volume will simply affect the position of equilibrium.