# Pressure Constant Kp from Kc

Calculator of the pressure constant Kp of a gas phase chemical reaction from the equilibrium constant Kc.

**Enter 'x' in the field to be calculated.**

## Answer

This tool calculates the Pressure Constant Kp of a chemical reaction from its Equilibrium Constant Kc.

`K_p = K_c * (R*T)^(\Delta_n)`

Kp: Pressure Constant

Kc: Equilibrium Constant

R: Ideal gas constant

T: temperature in Kelvin.

Δ_{n}: difference between the sum of the coefficients of gaseous products and the sum coefficients of gaseous reactants.

Pay attention to the consistency between the pressure unit and R (Ideal gas constant).

Kp has no unit but is always 'accompanied' by a standard pressure P_{0} which must be specified (rigorously `P_0` = 1 bar).

If P_{0} = 1 bar then R = 0.083144 l * bar/K* mol

If P_{0} = 1 atm then R = 0.082057 l*atm/K* mol

## Example of calculation of Kp

We consider the following chemical reaction:\(\ce{N2_{(g)}+3H2_{(g)} <=> 2NH3_{(g)}}\)

How to to calculate the pressure constant Kp of this chemical reaction knowing that Kc = 0.78 at T = 700 °C ?.

We enter the following data in the calculator:

- Pressure constant (Kp): x (unknown to calculate)

- Standard pressure: 1 bar

- Kc = 0.78

- Δ_{n} = -2 (since the sum of the coef. of the products = 2 and the sum of the coef. of the reactants = 1 + 3 = 4 therefore, Δ_{n} = 2 - 4 = -2)

- T = 700

- Unit T: °C (degree celcius)

Then, we get the following calculator: `Kp = 1.19*10^(-4)`

Note: As P_{0} = 1 **bar**, we've converted R (ideal gas constant) to the right unit R = 0.08314463 l.**bar**/ (K.mol)

## See also

Calculator of the equilibrium constant from partial pressures

Conversion of pressure units

Temperature unit conversion

Solution and Equilibrium Calculators

Chemistry Calculators