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Molecular weight (M.W.) (for molecular compounds) and formula weight (F.W.) (for non-molecular compounds), are older terms for what is now more correctly called the relative molar mass (M r). [8] This is a dimensionless quantity (i.e., a pure number, without units) equal to the molar mass divided by the molar mass constant .
The definition of molecular weight is most authoritatively synonymous with relative molecular mass; however, in common practice, use of this terminology is highly variable. When the molecular weight is given with the unit Da, it is frequently as a weighted average similar to the molar mass but with different units.
This template calculates the molecular mass (or molar mass) of a chemical compound. It is designed to be embedded in infoboxes {{ Infobox drug }} and {{ Chembox }} , but it can be used in-line just as well.
The molar mass constant, usually denoted by M u, is a physical constant defined as one twelfth of the molar mass of carbon-12: M u = M(12 C)/12. [1] The molar mass of an element or compound is its relative atomic mass (atomic weight) or relative molecular mass (molecular weight or formula weight) multiplied by the molar mass constant.
The mass-average molecular mass, M w, is also related to the fractional monomer conversion, p, in step-growth polymerization (for the simplest case of linear polymers formed from two monomers in equimolar quantities) as per Carothers' equation: ¯ = + ¯ = (+), where M o is the molecular mass of the repeating unit.
Graham's law can also be used to find the approximate molecular weight of a gas if one gas is a known species, and if there is a specific ratio between the rates of two gases (such as in the previous example). The equation can be solved for the unknown molecular weight.
The atomicity of homonuclear molecule can be derived by dividing the molecular weight by the atomic weight. For example, the molecular weight of oxygen is 31.999, [3] while its atomic weight is 15.879; [4] therefore, its atomicity is approximately 2 (31.999/15.879 ≈ 2).
The molar mass of a substance depends not only on its molecular formula, but also on the distribution of isotopes of each chemical element present in it. For example, the molar mass of calcium-40 is 39.962 590 98 (22) g/mol, whereas the molar mass of calcium-42 is 41.958 618 01 (27) g/mol, and of calcium with the normal isotopic mix is 40.078(4 ...