Equilibrium Constant

The equilibrium constant compares how much product and reactant is present once a reversible reaction has settled into a steady state at a given temperature. Each concentration is raised to its stoichiometric coefficient because the balance condition from the reaction quotient is derived from the reaction’s stoichiometry, so changing the coefficients changes the sensitivity of the ratio. A very large or very small value tells you which side is favored at equilibrium, but the value itself is only meaningful for a specific temperature.

Use this when analyzing reversible reactions in chemistry, especially to predict the equilibrium position or to compare a measured mixture with the expected equilibrium composition. It is also used in equilibrium calculations, such as finding an unknown concentration from known species at equilibrium.

• Using initial concentrations instead of equilibrium concentrations
• Forgetting to raise concentrations to their stoichiometric powers
• Including pure solids or pure liquids in the equilibrium expression