Molecular mass

Definition

Molecular mass is the sum of the atomic masses of all atoms in a molecule, typically expressed in atomic mass units (amu). It represents the total mass of a single molecule of a substance.

5 Must Know Facts For Your Next Test

1. Molecular mass is calculated by adding up the atomic masses of each atom in the molecular formula.
2. The unit for molecular mass is atomic mass units (amu), where 1 amu is defined as one-twelfth of the mass of a carbon-12 atom.
3. Molecular mass can be used to determine the molar mass, which is the mass of one mole of a substance and expressed in grams per mole (g/mol).
4. In chemical formulas, subscripts indicate how many times each element's atomic mass should be counted when calculating molecular mass.
5. Molecular mass is critical for stoichiometric calculations in chemical reactions to ensure proper reactant and product ratios.

Review Questions

• What units are used to express molecular mass?
• How do you calculate the molecular mass from a given chemical formula?
• Why is knowing the molecular mass important for stoichiometric calculations?

Related terms

Atomic Mass:

The weighted average mass of an atom of an element based on its isotopes, measured in atomic mass units (amu).

Mole:

A unit that measures an amount of substance containing Avogadro's number ($6.022 \times 10^{23}$) entities, such as atoms or molecules.

Stoichiometry:

The calculation of reactants and products in chemical reactions using balanced chemical equations.