Chemistry

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Kp Equilibrium Constant Calculator.

Calculate Kp from explicit partial pressures, stoichiometry, and a standard pressure.

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Kp: 1

Kp

1.00

How to Use

Kp = product(p/P°)^ν ÷ reactant(p/P°)^ν. All pressures use the same unit and P° is visible.

Use a named source for any material-specific coefficient. This page does not infer local rates, species tables, laboratory methods, or safety guidance.

Use Cases

Check equilibrium position

Determine whether products or reactants are favored at equilibrium by comparing the calculated Kp to 1. A Kp > 1 indicates products are favored, while Kp < 1 indicates reactants are favored.

Example: For N2 + 3H2 ⇌ 2NH3, if Kp = 4.5, products are favored.

Verify experimental data

Use measured partial pressures from an experiment to calculate Kp and compare with literature values to validate your results.

Example: Enter pressures from a lab run to see if Kp matches the known value.

Frequently Asked Questions

What is Kp in chemistry?
Kp is the equilibrium constant expressed in terms of partial pressures of gases. It relates the pressures of products and reactants at equilibrium, each raised to the power of their stoichiometric coefficients, and is dimensionless when divided by standard pressure.
How do I use this Kp calculator?
Enter the partial pressures of up to two products and two reactants, along with their stoichiometric coefficients from the balanced equation. Also provide the standard pressure (P°) in bar. The calculator computes Kp using the formula: (P_productA/P°)^coeffA * (P_productB/P°)^coeffB divided by (P_reactantA/P°)^coeffA * (P_reactantB/P°)^coeffB.
What units should I use for pressures?
All pressures (product and reactant partial pressures, and standard pressure) should be entered in bar. The calculator uses these values directly, so ensure consistency to get a correct dimensionless Kp.

Tips & Common Mistakes

Tips

  • Ensure the balanced chemical equation is correct before entering coefficients; they must match the stoichiometry.
  • Use consistent units: all pressures must be in bar, including the standard pressure P°.
  • If a species is not present, enter 0 for its pressure and coefficient, but note that a zero pressure will make Kp zero or undefined; ensure your reaction includes all species.
  • Double-check that you have assigned product and reactant pressures correctly; swapping them will invert Kp.

Common Mistakes to Avoid

  • Forgetting to divide each partial pressure by the standard pressure P°, which is essential for a dimensionless Kp.
  • Using coefficients that do not match the balanced equation, leading to incorrect exponents in the Kp expression.
  • Entering pressures in different units (e.g., atm instead of bar) without converting, which skews the result.

Last updated: August 13, 2026