Final answer:
Avogadro's Number is the term used to express the number of molecules without considering their weight, essentially counting particles in a mole, which is different from molecular mass.
Step-by-step explanation:
The expression of the number of molecules without regard to their weight is referred to as Avogadro's Number. This concept is fundamental in chemistry, particularly when discussing stoichiometry and the measurement of substances. Avogadro's Number, which is approximately 6.02 x 1023, represents the number of particles found in one mole of a substance and provides a way to count molecules through a process known as "counting by weighing". The coefficient in a chemical equation also gives the number of molecules of a substance but does not provide information on the weight of the molecules.
Unlike molecular mass, which combines the average masses of the atoms in a molecule, Avogadro's Number allows chemists to discuss and work with the number of molecules in a sample directly. Calculating the number of molecules in a given mass of compound involves determining the number of moles and then multiplying by Avogadro's Number to achieve a count.