What is the difference between gram formula mass and formula mass?

The terms "gram formula mass" and "formula mass" refer to similar concepts but may be used in slightly different contexts.

Formula Mass: This term generally refers to the sum of the atomic masses of all the atoms in a chemical formula. It is used to calculate the mass of a single molecule or formula unit of a substance. The units for formula mass are atomic mass units (amu) or unified atomic mass units (u). Formula mass is often used in chemistry to determine the relative mass of compounds or molecules.

Gram Formula Mass: Gram formula mass specifically refers to the formula mass of a substance expressed in grams per mole. It's essentially the molar mass of a substance, where the formula mass is expressed in grams. For example, the gram formula mass of water (H2O) is approximately 18 grams per mole. This term is more commonly used in the context of stoichiometry and chemical calculations involving masses.

In summary, while both terms refer to the mass of a chemical formula, "formula mass" is a more general term referring to the sum of atomic masses in a formula, while "gram formula mass" specifically denotes this mass expressed in grams per mole.