Pressure Constant Kp

Chemical reaction :
\(\ce{aA_{(g)} + bB__{(g)} <=> cC_{(g)} + dD_{(g)}}\) where molecules A and B are the reactants, C and D are the products of the reaction.
a, b, c and d are the coefficients of molecules A, B, C,D and `P_A, P_B, P_C, P_D` are partial pressures of A, B, C, D in bar (`P_0 = 1` bar).

Pressure Constant Kp formula : `K_p = \frac{(P_C/P_0)^c*(P_D/P_0)^d}{(P_A/P_0)^a*(P_B/P_0)^b}`

This tool calculates the equilibrium constant Kp for a chemical reaction in the gas phase. We assume that the standard pressure (or reference pressure) `P_0` = 1 bar.

We consider the following chemical reaction :
\(\ce{aA_{(g)} + bB_{(g)} <=> cC_{(g)} + dD_{(g)}}\)

- A, B, C and D are gaseous reactants and products
- a, b, c, d are the equation coefficients

Equilibrium Constant:
`K_p = \frac{(P_C/P_0)^c*(P_D/P_0)^d}{(P_A/P_0)^a*(P_B/P_0)^b}`

P₀: standard pressure is 1 bar
P_A: partial pressure of reactant (gas) A in bar
P_B: partial pressure of reactant (gas) B in bar
P_C: partial pressure of product (gas) C in bar
P_D: partial pressure of product (gas) D in bar

Note:
When a liquid or solid element is present in a gaseous reaction, the partial pressure is not significant for that element. In this case, the partial pressure P is replaced by 1 in the calculation formula of Kp.

Example of use

Consider the chemical reaction with the following gaseous components: oxygen, nitrogen and nitric oxide.
\(\ce{N2_{(g)} + O2_{(g)} <=> 2NO_{(g)}}\)

There are 2 reactants and one product.

Reactants:
A = `N_2`
B = `O_2`

The product:
C = `NO`

Coefficients:
a = 1
b = 1
c = 2

Then, the following values should be entered in the calculator:
- Field "Coefficients of Reactants" : 1 1
- Field "Coefficients of Products" : 2

Suppose that the partial pressures at equilibrium are (in bar):
`P_{N_2}` = 2.25
`P_{O_2}` = 8.2
`P_{NO}` = 5.2

So, the field "Partial pressure of reactants (in bar)" should be : 2.25 8.2
- the field "Partial product pressure (bar)" should be : 5.2

That leads to the following calculator : `Kp = 1.47`

See also

Conversion of pressure units
Equilibrium constant Kc calculator
Ionic Force Calculator
Solution and Equilibrium Calculators
Chemistry Calculators