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In chemistry, the molar mass (M) (sometimes called molecular weight or formula weight, ... As an example, the average molar mass of dry air is 28.96 g/mol. [5]
is the molecular mass of dry air, approximately 4.81 × 10 −26 in kg. [note 1], the specific gas constant for dry air, which using the values presented above would be approximately 287.050 0676 in J⋅kg −1 ⋅K −1. [note 1] Therefore:
The molecular mass (m) is the mass of a given molecule. Units of daltons (Da) are often used. [1] ... The terms "molecular mass", "molecular weight", and "molar mass ...
ISO TR 29922-2017 provides a definition for standard dry air which specifies an air molar mass of 28,965 46 ± 0,000 17 kg·kmol-1. [2] GPA 2145:2009 is published by the Gas Processors Association. It provides a molar mass for air of 28.9625 g/mol, and provides a composition for standard dry air as a footnote. [3]
for dry air Unit 287.052874 J⋅kg −1 ⋅K −1: ... so can the specific gas constant by dividing the Boltzmann constant by the molecular mass of the gas: ...
The average molecular weight of dry air, which can be used to calculate densities or to convert between mole fraction and mass fraction, is about 28.946 [16] or 28.96 [17] [18] g/mol. This is decreased when the air is humid. The relative concentration of gases remains constant until about 10,000 m (33,000 ft). [19]
Air is given a vapour density of one. For this use, air has a molecular weight of 28.97 atomic mass units, and all other gas and vapour molecular weights are divided by this number to derive their vapour density. [2] For example, acetone has a vapour density of 2 [3] in relation to air. That means acetone vapour is twice as heavy as air.
The mean molecular mass of dry air is 28.97 g/mol. The content of the gas may undergo significant variations from time to time or from place to place. The concentration of CO 2 and CH 4 vary by season and location.