Untitled - Kelly Walsh High School

214 CHEMISTRY FOR THE UTTERLY CONFUSED
Quick Tip
Don’t Forget!
The coefficients of the x’s will be the same as the coefficients in the equilibrium
reaction equation.
In order to complete the table we need to add each column to get the equilibrium
values:
I 2
Initial 0.500
I
0
Change x 2 x
Equilibrium 0.500 x 2 x
This type of table is an Initial/Change/Equilibrium (ICE) table. The acronym
comes from the first letter of the names for each row of the table. The bottom
row of the ICE table goes into your equilibrium expression:
K = 3.76 105 [2 x] 2
[I]
[0.500 x]
2
[I2 ]
There are two ways to complete the problem from this point. Your instructor
may specify one method or the other in which case you should do what your
instructor wishes. We will show you both methods.
The first method involves an assumption. Any time the value of the equilibrium
constant is very large or very small, an assumption is possible. In this case, the
constant is very small. A small equilibrium constant indicates that only a small
number of iodine molecules will break apart to become iodine atoms. This
means that x will be small. A small x value means that 0.500 x will be close to
0.500 M. As an assumption, we will assume that 0.500 x is 0.500 M.
Any time you make an assumption, you will need to check the validity of the
assumption. Your instructor will tell you what determines a valid assumption.