Calculations with Chemical Equations

Now that we understand the mole concept and mol-mol conversion factors, we're ready to do quantitative calculations. Consider the rusting of oxygen:

Method I:

Step 1	Determine moles of iron:
Step 2	Convert from moles of iron to moles of rust:
Step 3	Convert from moles of rust to mass of rust:

Method 2: Steps 1-3 above can be accomplished in one overall calculation by treating the problem like a dimensional analysis problem:

The second method is somewhat easier since it can be accomplished in one line. Let us do one more example:

Consider the combustion of butane:

If we need to recover 150 g of water, what mass of butane is necessary? The method 2 result is:

Most chemical calculations involving masses are carried out in a similar manner.