Kp Calculator

Kp Calculator

The Kp Calculator converts between equilibrium constants expressed in molar concentration ($K_c$) and partial pressure ($K_p$), or calculates $K_p$ directly from the partial pressures of gaseous reactants and products.

For a gaseous reaction $aA + bB \rightleftharpoons cC + dD$, the relationship between $K_c$ and $K_p$ is:

$$K_p = K_c \cdot (R \cdot T)^{\Delta n}$$

where $R$ is the gas constant, $T$ is temperature in kelvin, and $\Delta n$ is the change in moles of gaseous products minus gaseous reactants. When $\Delta n = 0$, $K_p$ equals $K_c$.

The equilibrium constant in terms of partial pressure is:

$$K_p = \frac{P_c^c \cdot P_d^d}{P_a^a \cdot P_b^b}$$

Solids and liquids are omitted from this expression because their activities are taken as 1. For the Haber process example with $K_c = 0.0227$ at 298 K and $\Delta n = -2$, $K_p \approx 3.8 \times 10^{-5}$ atm.

Related tools: Equilibrium Constant Calculator, Concentration Calculator, and Arrhenius Equation Calculator.