Kp Calculator

Difference in moles of gaseous products vs gaseous reactants.
°C
Converted to Kelvin internally.
Chemistry

Convert between Kp (equilibrium constant in terms of partial pressures) and Kc (equilibrium constant in terms of concentrations).

Formula

Kp = Kc × (RT)^Δn
  • R = 0.08206 L·atm/(mol·K); T in Kelvin.
  • Δn = moles of gaseous products − moles of gaseous reactants.
  • If Δn = 0, Kp = Kc.
  • Valid for ideal gas mixtures.

N₂ + 3H₂ ⇌ 2NH₃ at 25°C, Kc = 0.5

Inputs
  • Kc (concentration equilibrium constant): 0.5
  • Δn (moles gas products − reactants): -2
  • Temperature: 25 °C

Δn = 2 − 4 = −2. RT = 0.08206 × 298.15 = 24.46. Kp = 0.5 × (24.46)^−2 = 8.35×10⁻⁴.

Frequently asked questions

When is Kp = Kc?
When Δn = 0 (equal moles of gas on both sides of the equation).
What is the difference between Kp and Kc?
Kp uses partial pressures; Kc uses molar concentrations. They are related by (RT)^Δn.