E - Equilibrium Calculations and ICE Tables (Lesson)

Equilibrium Calculations and ICE Tables

In the previous lessons, concepts involving the equilibrium constant and the equilibrium expression were described as well as how to calculate the value of the equilibrium constant if provided with the concentrations (or partial pressures) of substances in a system at equilibrium. Because the equilibrium constant remains the same at a given temperature, it is also possible to determine the value of the equilibrium constant when the concentration of only one component of the system is known.

For example, consider the hypothetical equilibrium shown below:

A (g)  $\rightleftharpoons$  2 B (g)

Suppose that a reaction mixture exists where the initial concentrations of A and B are 0.50 M and 0.00 M, respectively. After equilibrium is reached, it is determined that the concentration of A decreased to 0.10 M. To calculate the equilibrium constant, an organization technique known as an ICE table (shown below) is frequently used:

ICE TABLE

	[A]	[B]
Initial	0.50	0.00
Change	-0.40	+0.80
Equilibrium	0.10	0.80

As indicated in the table, the acronym ICE refers to Initial, Change, and Equilibrium concentrations. Notice that stoichiometry is utilized to determine the change in concentrations between the initial and equilibrium conditions. If the [A] decreases by 0.40 M (0.50 - 0.10), then the [B] will increase by twice that amount due to the 2:1 mol-to-mol ratio. Now that the equilibrium concentrations are known, it is possible to determine the equilibrium constant for this reaction:

$K=\frac{\left\lbrack B\right\rbrack^2}{\left\lbrack A\right\rbrack}=\frac{\left(0.80\right)^2}{\left(0.10\right)}=6.4$

You Try It!

In the following self-assessment activity, find the equilibrium constant. Click on the plus sign to check your answer!

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