1. Education
You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum

Equilibrium Constant Example Problem

Calculating Equilibrium Constant


This example problem demonstrates how to find the equilibrium constant of a reaction from equilibrium concentrations of reactants and products.


For the reaction

H2(g) + I2(g) ↔ 2 HI(g)

At equilibrium, the concentrations are found to be

[H2] = 0.106 M
[I2] = 0.035 M
[HI] = 1.29 M

What is the equilibrium constant of this reaction?


The equilibrium constant (K) for the chemical equation

aA + bB ↔ cC + dD

can be expressed by the concentrations of A,B,C and D at equilibrium by the equation

K = [C]c[D]d/[A]a[B]b

For this equation, there is no dD so it is left out of the equation.

K = [C]c/[A]a[B]b

Substitute for this reaction

K = [HI]2/[H2][I2]
K = (1.29 M)2/(0.106 M)(0.035 M)
K = 4.49 x 102


The equilibrium constant of this reaction is 4.49 x 102.

©2014 About.com. All rights reserved.