# Question #19ea3

Jan 16, 2014

Mole ratios are central to stoichiometric calculations because they bridge the gap when we have to convert between the mass of one substance and the mass of another.

Stoichiometry refers to the coefficients of a balanced chemical reaction equation. The chemical equations show the proportions of reactant and product molecules. For example, if we have a reaction such as

• ${N}_{2}$ + $3 {H}_{2}$ $\to$ $2 N {H}_{3}$

• We know that hydrogen and nitrogen molecules react in a 3:1 proportion.

The coefficients in the balanced chemical equation show the relative numbers of moles of the substances in the reaction. As a result, you can use the coefficients in conversion factors called mole ratios. The mole ratio of hydrogen to nitrogen is also 3:1.

• When you balance equations, you are using moles to correspond the number of molecules in the reaction. Moles aren’t grams, because every substance has its own molar mass. Therefore, we have to convert the grams of each substance to the corresponding number of moles.

Mole ratios bridge the gap when we have to convert from grams of one substance to grams of another.