Calculator
For aA + bB ⇌ cC + dD, enter equilibrium concentrations and coefficients to calculate Kc = [C]^c[D]^d / [A]^a[B]^b.
Formula and assumptions
Kc = [products]^coefficients / [reactants]^coefficients
Enter equilibrium concentrations for the species included in the expression. The generic four-term form represents aA + bB ⇌ cC + dD.
Assumption: Entries represent equilibrium concentrations for the species included in the expression.
Variables and units
Worked example
For A + B ⇌ C with [A] = 1, [B] = 1 and [C] = 2, Kc = 2.
Writing the Kc expression
For N₂ + 3H₂ ⇌ 2NH₃, Kc = [NH₃]² / ([N₂][H₂]³): each concentration is raised to its coefficient in the balanced equation. With [N₂] = 0.50 M, [H₂] = 1.50 M and [NH₃] = 0.30 M, Kc = 0.09 / (0.50 × 3.375) ≈ 0.0533. Pure solids and liquids are left out of the expression, and Kc applies only at the temperature it was measured at.
Important limits
Activities, solids, pure liquids, temperature dependence and reaction balancing are not evaluated.
Reference and related tools
OpenStax: Equilibrium constants. Return to Chemistry Calculators for the other tools in this group.