wwwwwwwwwwwwwwww

Problem:

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?

Solution

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

Example: Initially, a mixture of 0.100 M NO, 0.050 M H2, 0.100 M H2 O was allowed to reach equilibrium (initially there was no N2 ). At equilibrium the concentration of NO was found to be 0.062 M. Determine the value of the equilibrium constant, Kc , for the reaction:

Write the equilibrium expression for the reaction.

Check to see if the amounts are expressed in moles per liter (molarity) since Kc is being . In this example they are.
Create an ICE chart that expresses the initial concentration, the change in concentration, and the equilibrium concentration for each species in the reaction. From the chart you can determine the changes in the concentrations of each species and the equilibrium concentrations. From the example, we start with the folowing information. NO
H2
N2
H2O
Initial Concentration (M)
0.100
0.0500
0
0.100
Change in Concentration (M)
- 2 x
- 2 x
+ x
+ 2 x
Equilibrium Concentration (M)
0.062

The change in concentration of the NO was (0.062 M - 0.100M) = - 0.038 M. Thus -2 x = - 0.038 and x = 0.019. Note: the negative sign indicates a decreasing concentration, not a negative concentration. The changes in the other species must agree with the stoichiometry dictated by the balance equation. The hydrogen will also change by - 0.038 M, while the nitrogen will increase by + 0.019 M and the water will