# Pressure Constant Kp from Kc

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

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.
Δn: 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 P0 which must be specified (rigorously P_0 = 1 bar).
If P0 = 1 bar then R = 0.083144 l * bar/K* mol
If P0 = 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
- Δn = -2 (since the sum of the coef. of the products = 2 and the sum of the coef. of the reactants = 1 + 3 = 4 therefore, Δn = 2 - 4 = -2)
- T = 700
- Unit T: °C (degree celcius)

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

Note: As P0 = 1 bar, we've converted R (ideal gas constant) to the right unit R = 0.08314463 l.bar/ (K.mol)