How is molar mass defined?

Molar mass is defined as the mass of one mole of a substance, measured in grams per mole. This concept is fundamental in chemistry because it allows for the conversion between the amount of a substance in moles and its mass in grams, which is essential for stoichiometric calculations in chemical reactions.

When you have a chemical formula, the molar mass can be calculated by adding up the atomic masses of each element in that formula, taking into account the number of atoms of each element. For example, the molar mass of water (H2O) is calculated as the sum of the molar masses of two hydrogen atoms and one oxygen atom, resulting in approximately 18 grams per mole.

The other options do not accurately define molar mass. The first option discusses the total mass in liters, which relates to volume and does not address the concept of moles. The third option refers to the mass of a single atom in atomic mass units, which is a different measurement and does not represent the concept of moles. The fourth option addresses the average mass of isotopes of an element, which pertains to atomic mass and not specifically to the molar mass relevant for moles in a chemical context.