Chemistry Reference
In-Depth Information
Step 2. Insert the required conversion factors to change between units. The
conversion factors will be in fraction form, and they will be orientated in
such a way that we can cross-cancel the units that we don't want, and keep
the units that we do want. In this particular example, we will only need
one conversion factor, 1 hour = 60 minutes. We will put the unit for
hours on the top, so that we will end with hours on the top. We will put
the unit for minutes on the bottom, because we want to cross-cancel
the minutes that we already have on the top.
1 h
60 min
90 min ×
= h
Step 3. Cancel the units that appear on both the top and bottom, and solve the
math. Notice how we have minutes on both the top and the bottom?
We can cross-cancel them, because minutes divided by minutes would
give us the number “1”.
1 h
60 min
90 h
60
90 min ×
=
= 1.5 h
Now, I am sure that this example didn't convince you of the necessity
of the factor-label method, because you can do the conversion in your head.
Remember that we started with an easy example, just to show you how it
works. As the examples get more difficult, the usefulness of the method
will become clearer. Let's try a slightly harder example now.
Example 2
If a snail moves with a constant velocity of 2.38 inches/minute, how
many yards could it travel in 1 hour?
Step 1. Show what you are given on the left side of your workspace, and the units
that you want on the right side of your workspace.
2.38 in
min
yd
h
=
Step 2. Insert the required conversion factors to change between units. The
conversion factors will be in fraction form, and they will be orientated in
such a way that we can cross-cancel the units that we don't want and keep
the units that we do want. In this example, we will need either 2 or 3
conversion factors, depending on how you choose to solve it. If you
convert inches to yards directly, you will only need 2 conversion factors.
For the sake of clarity, I will use two steps to convert inches to yards
and will use a total of 3 conversion factors.
