Equilibrium Constant Calculator
Calculate the equilibrium constant (Kc) from equilibrium concentrations and coefficients.
Enter the equilibrium concentration (mol/L) for each species and its stoichiometric coefficient. Leave a species blank if it is not part of the reaction; it will be treated as a factor of 1. Coefficients default to 1.
Reactants
concentration · coefficient a
concentration · coefficient b
Products
concentration · coefficient c
concentration · coefficient d
Equilibrium Constant (Kc)
Calculation Steps
What Is the Equilibrium Constant?
The equilibrium constant Kc describes the ratio of product concentrations to reactant concentrations, each raised to the power of its stoichiometric coefficient, once a reversible reaction has reached equilibrium. A large Kc means the equilibrium favors the products, while a small Kc means it favors the reactants. Kc is constant at a given temperature.
The Kc Formula
For the reversible reaction aA + bB ⇌ cC + dD, the equilibrium constant is:
Kc = ( [C]^c × [D]^d ) / ( [A]^a × [B]^b )
- • [A], [B], [C], [D] = equilibrium concentrations (mol/L)
- • a, b, c, d = stoichiometric coefficients
- • Pure solids and liquids are omitted from the expression
Note: Kc uses molar concentrations and applies only to species in solution or gas phase; pure solids and liquids are excluded. The value of Kc depends on temperature, so it must be evaluated at the temperature of interest. For gas-phase reactions you may instead use Kp, which is based on partial pressures.