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Heptane or n-heptane is the straight-chain alkane with the chemical formula H 3 C(CH 2) 5 CH 3 or C 7 H 16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating scale (the 100 point is 100% iso-octane ).
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 terms "molecular mass", "molecular weight", and "molar mass" may be used interchangeably in less formal contexts where unit- and quantity-correctness is not needed. The molecular mass is more commonly used when referring to the mass of a single or specific well-defined molecule and less commonly than molecular weight when referring to a ...
The interest stems from that accurate measurements of the unit cell volume, atomic weight and mass density of a pure crystalline solid provide a direct determination of the Avogadro constant. [3] The CODATA recommended value for the molar volume of silicon is 1.205 883 199 (60) × 10 −5 m 3 ⋅mol −1, with a relative standard uncertainty of ...
The mass average molar mass (often loosely termed weight average molar mass) is another way of describing the molar mass of a polymer. Some properties are dependent on molecular size, so a larger molecule will have a larger contribution than a smaller molecule.
For example, Paraffin has very large molecules and thus a high heat capacity per mole, but as a substance it does not have remarkable heat capacity in terms of volume, mass, or atom-mol (which is just 1.41 R per mole of atoms, or less than half of most solids, in terms of heat capacity per atom).
In SI units, number density is measured in m −3, although cm −3 is often used. However, these units are not quite practical when dealing with atoms or molecules of gases, liquids or solids at room temperature and atmospheric pressure, because the resulting numbers are extremely large (on the order of 10 20).
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.