Kp to Kc Calculator

Convert between Kp (pressure-based) and Kc (concentration-based) equilibrium constants using Kp = Kc*(RT)^(delta-n). Find delta-n from the balanced equation.

⚖️ Equilibrium📐 Kp = Kc(RT)Δn🧪 Chemistry

Kc or Kp (value to convert from)

Δn (moles gas products - reactants)

Temperature T (K)

Convert direction

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Kp to Kc Calculator	See formula	Kp = Kc(RT)Δn	dimensionless

Step-by-Step Examples

Example 1

N2+3H2 to 2NH3

delta-n = 2-4 = -2. Kc=6.02 at 500 K. Find Kp.

Kp = Kc(RT)^delta-n
Kp = 6.02 x (0.08206x500)^(-2)
Kp = 6.02 x (41.03)^(-2) = 6.02/1683.5 = 0.00358

✓ Kp = 3.58x10^-3

Example 2

CO+H2O to CO2+H2

delta-n = 2-2 = 0. Kc=Kp (always when delta-n = 0).

Kp = Kc(RT)^0 = Kc x 1 = Kc
Kp = Kc for all temperatures

✓ Kp = Kc when delta-n = 0

Example 3

H2O(g) Decomposition

2H2O(g) to 2H2+O2. delta-n = 3-2 = +1. Kp = 1.00x10^-10 at 1000 K. Find Kc.

Kc = Kp/(RT)^1 = 1.00x10^-10/(0.08206x1000)
Kc = 1.00x10^-10/82.06 = 1.22x10^-12

✓ Kc = 1.22x10^-12

Real-World Applications

🏭

Gas-Phase Reactions

Kp is natural for gas-phase equilibria; Kc for solution reactions. Must convert between when needed.

📊

Thermodynamics

Standard Gibbs energy uses Kp: dG-deg = -RT ln Kp (for gas-phase reactions).

🧪

Physical Chemistry

Understanding the Kp/Kc relationship deepens knowledge of ideal gas behavior.

⚗️

Atmospheric Chemistry

Gas-phase equilibria (ozone, NOx) are described using Kp in pressure units.

Common Mistakes to Avoid

⚠️

Calculate delta-n from balanced equation

delta-n = moles of gaseous products - moles of gaseous reactants. Ignore solids and liquids.

⚠️

R must match pressure units

R=0.08206 L-atm/mol-K when Kp uses atm. R=8.314 J/mol-K when using Pa. Keep units consistent.

⚠️

When delta-n = 0, Kp = Kc

This is a useful check: for CO+H2O to CO2+H2, delta-n=0, so Kp always equals Kc.

Frequently Asked Questions

Why are there two forms of equilibrium constant? ▾

Kc uses molar concentrations (mol/L); Kp uses partial pressures (atm). Both are valid; the relationship is Kp = Kc(RT)^delta-n.

Which should I use? ▾

Kp is more convenient for gas-phase reactions. Kc for reactions in solution. Both give the same equilibrium position.

What is the standard state for Kp? ▾

Kp uses pressures relative to 1 atm standard. So Kp is dimensionless when written as p_i/p-deg.

How does Kp relate to dG? ▾

For gas-phase: dG-deg = -RT ln Kp. For solution: dG-deg = -RT ln Kc. They differ when delta-n is not zero.

What if some species are not gases? ▾

Only gaseous species appear in Kp. Pure solids and liquids, and dissolved species, appear in Kc but not Kp.

Related Chemistry Calculators

Formula Explorer connections

Interpretation: This formula describes how reactants, products, ions or phases distribute when opposing processes reach equilibrium. Assumption: Use equilibrium rather than initial concentrations, correct stoichiometric exponents, and the specified temperature; activities may replace concentrations in nonideal systems.

Langmuir Adsorption Isotherm Calculator →Le Chatelier's Principle Calculator →Le Chatelier Principle Calculator →Chemistry Formula Explorer →