Equilibrium Constant Calculator (Kc & Kp)

Equilibrium Constant Calculator (Kc & Kp). The Equilibrium Constant Calculator finds how far a chemical reaction proceeds before it reaches a stable, balanced state — a value chemists use to predict whether products or reactants dominate at equilibrium. Select your Calculation Type — calculate Kc from molar concentrations, Kp from partial pressures, or convert between the two — then enter your reactant/product values and stoichiometric coefficients. The calculator returns the Equilibrium Constant, along with the Converted Constant, Δn (change in moles), and Reaction Direction. Also try the Rate Constant (k) — Rate Constant.

Results

Equilibrium Constant

Converted Constant

Δn (Change in moles)

Reaction Direction

What is the difference between Kc and Kp?

Kc is the equilibrium constant expressed in terms of molar concentrations, while Kp is expressed in terms of partial pressures. Kc is used for reactions in solution, while Kp is used for gas-phase reactions. See also our use the Mass Balance Calculator.

How do I convert between Kc and Kp?

Use the relationship Kp = Kc(RT)^Δn, where R is the gas constant (0.0821 L·atm/mol·K), T is temperature in Kelvin, and Δn is the change in moles of gas (products - reactants).

What does it mean if K > 1 or K < 1?

If K > 1, the equilibrium favors products (forward reaction is favored). If K < 1, the equilibrium favors reactants (reverse reaction is favored). K = 1 means equal concentrations of reactants and products.

How do stoichiometric coefficients affect the equilibrium constant?

Stoichiometric coefficients become exponents in the equilibrium expression. For aA + bB ⇌ cC + dD, K = [C]^c[D]^d/[A]^a[B]^b. Larger coefficients increase the impact of that species on the equilibrium.

What factors change the equilibrium constant?

Only temperature changes the equilibrium constant. Concentration, pressure, and catalysts do not change K, but they can shift the equilibrium position to reach the same K value.

How do I calculate Δn for the Kc to Kp conversion?

Δn = (sum of coefficients of gaseous products) - (sum of coefficients of gaseous reactants). Count only gas-phase species; exclude solids and liquids from the calculation. You might also find our Kp Calculator useful.