The key difference between molar mass and molecular mass is that the molar mass gives the average mass of the molecule whereas the molecular mass gives the mass of a single molecule.
Atoms can join together in various combinations to form molecules and other compounds. Molecular structures give the exact ratios of atoms; thus, we can write molecular formulas for compounds. These are important in determining the molecular masses or molar masses. We can characterize molecules with their masses. Knowing this is really useful in laboratory work when measuring the compounds for reactions.
