# Pressure Constant Kp

**Calculator of the pressure constant of a gas phase of a chemical reaction.**

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}`

Do not enter molecules symbols like O2, H2 ... Enter data separated by space(s).Powers of 10 : input

**2.5*10^-3**or

**2.5e-3**for [A] = `2.5*10^(-3)` mol/l

## Answer

Steps

Step 1. Chemical equation

\(\ce{A + B <=> 2C}\)

Step 2. Partial pressures are reported to reference pressure `P_0` = 1 bar

`P_A/P_0 = 2.25`

`P_B/P_0 = 8.2`

`P_C/P_0 = 5.2`

Step 3. Calculation Formula

`K_p = \frac{(P_C/P_0) ^2}{(P_A/P_0) (P_B/P_0) }`

Step 4. Calculation

`K_p = \frac{ (5.2)^2}{ (2.25)^1* (8.2)^1}`

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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}`

P_{0}: 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