Stoichiometry . Silicon to be used in computer chips is manufactured by a process represented by the following reaction:
A sample of 225 g of silicon tetrachloride, SiCl_{4} , is reacted with an excess (more than necessary) of Mg. How many moles of Si are produced?
Strategy : To solve this example, we first convert grams of SiCl_{4} to moles of SiCl_{4} , then moles of SiCl_{4} to moles of Si.
Step 1: First, we convert grams of SiCl_{4} to moles of SiCl_{4} . For this calculation we use the conversion factor 1 mol SiCl_{4} = 170 g SiCl_{4} :
255 \cancel{g SiCl_{4} }\times \frac{1 mol SiCl_{4}}{170 \cancel{g SiCl_{4} } } = mol SiCl_{4}
Step 2: To convert moles of SiCl_{4} to moles of Si, use the conversion factor 1 mol SiCl_{4} = 1 mol Si, which we obtain from the balanced chemical equation. Now we do the arithmetic and obtain an answer of 1.32 mol Si:
255 g SiCl_{4} \times \frac{1 \cancel { mol SiCl_{4}}}{170 \cancel{g SiCl_{4} } }\frac{1 mol Si}{1 \cancel { mol SiCl_{4}}} =1.32 mol Si