How do you convert grams of a substance to moles?

To convert grams of a substance to moles, you divide the mass of the substance (in grams) by its molar mass (in grams per mole). This process relies on the definition of a mole, which represents a specific number of particles (Avogadro's number, approximately (6.022 \times 10^{23})). The molar mass is the weight of one mole of a substance and is unique for each compound, reflecting its molecular composition.

When you divide the mass of the substance by its molar mass, you effectively determine how many "mole units" are contained in that mass. For example, if you have 18 grams of water (with a molar mass of about 18 g/mol), dividing gives you 1 mole of water. This conversion is foundational in stoichiometry, allowing chemists to relate the amounts of reactants and products in a chemical reaction.