The molar mass of a substance is defined as the mass of one mole of that substance. It is typically expressed in units of grams per mole (g/mol). The molar mass can be calculated by summing the average atomic masses of the constituent atoms in the substance.
The average atomic mass of an element is the weighted average of the masses of its isotopes, taking into account their relative abundances. Each isotope contributes to the average atomic mass based on its mass and its abundance in nature.
To calculate the molar mass of a substance, you add up the average atomic masses of all the atoms present in the chemical formula of that substance. For example, in the chemical formula for water (H₂O), you have two hydrogen atoms and one oxygen atom. You would look up the average atomic masses of hydrogen and oxygen from the periodic table and add them together to get the molar mass of water.
The molar mass is a conversion factor that allows you to convert between the mass of a substance and the number of moles of that substance, using Avogadro's number (6.022 × 10^23) as the bridge between atoms and moles.
So, in summary, the molar mass of a substance is the sum of the average atomic masses of the atoms in that substance, which allows you to convert between mass and moles in chemical calculations.