Does the equilibrium constant (K) have units?

The equilibrium constant ( K ) is a unitless quantity because it is defined as the ratio of the concentrations (or partial pressures) of products to the reactants, each raised to the power of their respective stoichiometric coefficients. In a chemical equilibrium expression, you typically have the form:

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

where brackets denote concentration in moles per liter (mol/L), and a, b, c, and d are the coefficients from the balanced chemical equation. When you calculate ( K ), the concentrations of the products in the numerator are divided by the concentrations of the reactants in the denominator.

If the number of moles of products and reactants are balanced (i.e., the sum of the coefficients of products equals the sum of the coefficients of reactants), the units cancel out, resulting in a dimensionless number. However, if there is an imbalance, then there will be a certain concentration or pressure unit associated with ( K ).

In summary, while the equilibrium constant can sometimes appear to have units based on the specific reaction, it is considered unitless in terms of its fundamental definition, particularly in standardized units commonly referenced