The equilibrium constant in concentration units: Kc = [products]^coefs / [reactants]^coefs. It is constant at a given temperature.

What is the difference between Q and Kc?

Q has the same form but uses the current (not necessarily equilibrium) concentrations. If Q Kc, backward; if Q = Kc, it is at equilibrium.

Why don't solids and pure liquids appear in Kc?

Their activities are taken as 1 because their concentrations are fixed. Only gases and species in solution appear.

Does Kc change with temperature?

Yes. Kc is constant only at a fixed temperature. Heating an endothermic reaction increases Kc; cooling decreases it. Concentration or pressure changes shift the position of equilibrium but do not change Kc.

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NSW · HSCChemistry

Equilibrium constant calculator

Enter the coefficients and equilibrium concentrations for any reaction aA + bB ⇌ cC + dD. Get Kc.

Inputs

Reaction: aA + bB ⇌ cC + dD. Enter the stoichiometric coefficients and the equilibrium concentrations.

abcd

[A] (mol/L)[B] (mol/L)[C] (mol/L)[D] (mol/L)

Result

1.000

Kc = [C]^c [D]^d / ([A]^a [B]^b). The same formula gives Q if the concentrations are not at equilibrium (Q < Kc means reaction shifts forward).

How this calculator works

Kc = [C]^c [D]^d / ([A]^a [B]^b). The calculator raises each equilibrium concentration to its stoichiometric coefficient and multiplies/divides as the formula requires.

Common questions

What is Kc?: The equilibrium constant in concentration units: Kc = [products]^coefs / [reactants]^coefs. It is constant at a given temperature.
What is the difference between Q and Kc?: Q has the same form but uses the current (not necessarily equilibrium) concentrations. If Q < Kc the reaction goes forward; if Q > Kc, backward; if Q = Kc, it is at equilibrium.
Why don't solids and pure liquids appear in Kc?: Their activities are taken as 1 because their concentrations are fixed. Only gases and species in solution appear.
Does Kc change with temperature?: Yes. Kc is constant only at a fixed temperature. Heating an endothermic reaction increases Kc; cooling decreases it. Concentration or pressure changes shift the position of equilibrium but do not change Kc.