# 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

K_p = 1.47

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}

input P_A P_B ... (spaces separated)
input P_C P_D ... (spaces separated)
a b ... (spaces separated)
c d ... (spaces separated)

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
PA: partial pressure of reactant (gas) A in bar
PB: partial pressure of reactant (gas) B in bar
PC: partial pressure of product (gas) C in bar
PD: 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