Equilibrium Constant Calculator
Determine the equilibrium constant for reactions of the form aA + bB ⇌ cC + dD, with optional conversion between Kc and Kp.
Kc
0.25
How to Use This Calculator
Identify stoichiometry
Balance the reaction and record coefficients for each species.
Provide concentrations or partial pressures
Enter equilibrium values of reactants and products (mol/L or atm).
Select Kc or Kp mode
Choose Kp for gas-phase reactions where partial pressures are known and supply temperature and Δn.
Review results
The calculator displays Kc and optionally Kp, offering quick insight into reaction equilibrium.
Formula
Kc = Π([products]^{stoichiometry}) / Π([reactants]^{stoichiometry})
Kp = Kc (RT)^{Δn}
Δn = Σ ν_products(g) − Σ ν_reactants(g). R is 0.082057 L·atm·mol⁻¹·K⁻¹ when working with atm and liters.
Example
For N₂ + 3H₂ ⇌ 2NH₃ (Δn = −2) with concentrations 0.2, 0.3, 0.15, 0.1 M, Kc = (0.15²)/(0.2 × 0.3³) ≈ 1.39.
Full Description
Equilibrium constants quantify the composition of mixtures at equilibrium. Kc uses molar concentrations, while Kp relies on partial pressures for gas-phase systems.
This calculator assists with coursework and practical chemistry by handling stoichiometric exponents and converting between Kc and Kp when temperature and Δn are known.
Frequently Asked Questions
Do I need to include pure solids or liquids?
No. Pure solids and liquids have activity 1 and are omitted from the expression.
Why are coefficients exponents?
Derived from the law of mass action, each species concentration is raised to its stoichiometric coefficient.
Can I mix concentration units?
All concentrations or pressures must use consistent units (e.g., mol/L or atm) for the ratios to be dimensionless.
What if Δn is zero?
Then Kp = Kc. The equilibrium constant is independent of temperature scaling factors in that case.
Does this handle more than four species?
This version covers a generic four-species reaction. For more species, extend the formula accordingly.