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Equilibrium Constant Formula

If the concentrations of reactants and products are same, one can call this reaction as equilibrium reaction. If A and B are the reactants, C and D are products, then an equilibrium reaction can be written as, A+B → C+D. From this reaction equation, we can calculate the equilibrium constant, $K_{c}$.
The formula for the equilibrium constant is,

where A, B, C and D are the molar concentrations

a, b, c and d are the respective coefficients

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Equilibrium Constant Problems

Problems related to equilibrium constant are given below:

Solved Examples

Question 1: Calculate the equilibrium constant of the following equation.
Na2O+H2O→2NaOH; the concentration of each reactants are NaOH = 0.23M, Na2O = 0.015M and H2O = 0.1M
Solution:

Given equation is,
Na2O+H2O→2NaOH
The molar concentration is,
NaOH = 0.23M, Na2O = 0.015M and H2O = 0.1M
The formula for equilibrium constant is given by,

$K_{c}$ = $\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$

$K_{c}$ = $\frac{[0.23]^{2}}{[0.015]^{1}[0.1]^{1}}$

$K_{c}$ = 35.266

Question 2: Calculate the equilibrium constant for the following equation
2HNO3 → N2O5+H2O; the molar concentration is HNO3 = 0.05, N2O5 = 0.3 and H2O = 0.1
Solution:

Given equation is,
2HNO3 → N2O5+H2O
The molar concentration is HNO3 = 0.05, N2O5 = 0.3 and H2O = 0.1
The formula for equilibrium constant is given by,

$K_{c}$ = $\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$

$K_{c}$ = $\frac{[0.3]^{1}[0.1]^{1}}{[0.05]^{2}}$

$K_{c}$ = 12

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