Reaction Equations and the Molar Ratio

The mole can be used to quantify reactions. For instance, imagine eating a giant cookie containing 1.20 mol of sucrose (sugar). This would be metabolised in our bodies to produce carbon dioxide and water:

Because we know how many moles of sucrose we have, stoichiometry can be used to determine the relative amounts of other reactants and products - but only if the equation is first balanced.

In order to balance an equation, the number of atoms of each element must be the same on both sides of the equation. So, for the metabolism of sucrose, the balanced reaction equation is given by...

Now that we have a balanced equation, we can determine the amount of carbon dioxide and water that is produced by the metabolism of 1.20 mol of sucrose.

In the equation for the metabolism of sucrose, the molar ratios are 1:12:12:11, respectively. This means that 1.20 mol of sucrose will react with 14.4 mol of oxygen to produce 14.4 mol of carbon dioxide and 13.2 mol of water. Thus, balanced equations and molar ratios enable us to quantify chemical reactions.