# What conversion factor is always used in stoichiometry problems?

Apr 27, 2015

The conversion factor that is always used in stoichiometry problems is the mole to mole ratio for elements or compounds in the balanced equation. Another conversion factor that is commonly used in stoichiometry is the molar mass, or g/mol.

For example, the reaction between hydrogen and oxygen gas to form water can be represented by the balanced equation "2H"_2("g") + "O"_2("g")$\rightarrow$$\text{2H"_2"O(g)}$ .

The mole to mole ratio for oxygen and water is $\left(1 \text{mol O"_2)/(2 "mol H"_2"O}\right)$ or $\left(2 {\text{mol H"_2"O")/(1 "mol O}}_{2}\right)$ .

If you are given the mass of one or more reactants or products, you can use its molar mass to convert its mass to moles. The molar mass can be used as a conversion factor as $\left(\text{grams")/(1 "mol}\right)$ or $\left(1 \text{mol")/("grams}\right)$ .

For example, if the mass of oxygen is 8.35 g, you can use its molar mass of 15.999 g/mol to convert its mass to moles.

8.35 cancel("g O"_2)xx(1 "mol O"_2)/(15.999 cancel("g O"_2))=0.522 "mol O"_2