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Untitled - Kelly Walsh High School

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214 CHEMISTRY FOR THE UTTERLY CONFUSED<br />

Quick Tip<br />

Don’t Forget!<br />

The coefficients of the x’s will be the same as the coefficients in the equilibrium<br />

reaction equation.<br />

In order to complete the table we need to add each column to get the equilibrium<br />

values:<br />

I 2<br />

Initial 0.500<br />

I<br />

0<br />

Change x 2 x<br />

Equilibrium 0.500 x 2 x<br />

This type of table is an Initial/Change/Equilibrium (ICE) table. The acronym<br />

comes from the first letter of the names for each row of the table. The bottom<br />

row of the ICE table goes into your equilibrium expression:<br />

K = 3.76 105 [2 x] 2<br />

[I]<br />

[0.500 x]<br />

2<br />

[I2 ]<br />

There are two ways to complete the problem from this point. Your instructor<br />

may specify one method or the other in which case you should do what your<br />

instructor wishes. We will show you both methods.<br />

The first method involves an assumption. Any time the value of the equilibrium<br />

constant is very large or very small, an assumption is possible. In this case, the<br />

constant is very small. A small equilibrium constant indicates that only a small<br />

number of iodine molecules will break apart to become iodine atoms. This<br />

means that x will be small. A small x value means that 0.500 x will be close to<br />

0.500 M. As an assumption, we will assume that 0.500 x is 0.500 M.<br />

Any time you make an assumption, you will need to check the validity of the<br />

assumption. Your instructor will tell you what determines a valid assumption.

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