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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.
The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear counter-intuitive. This occurs because the molar mass of water vapor (18 g/mol) is less than the molar mass of dry air [ note 2 ] (around 29 g/mol).
The saturation vapor density (SVD) is the maximum density of water vapor in air at a given temperature. [1] The concept is related to saturation vapor pressure (SVP). It can be used to calculate exact quantity of water vapor in the air from a relative humidity (RH = % local air humidity measured / local total air humidity possible ) Given an RH percentage, the density of water in the air is ...
Continental and superior air masses are dry, while maritime and monsoon air masses are moist. Weather fronts separate air masses with different density (temperature or moisture) characteristics. Once an air mass moves away from its source region, underlying vegetation and water bodies can quickly modify its character. Classification schemes ...
Water vapor and dry air density calculations at 0 °C: The molar mass of water is 18.02 g/mol, as calculated from the sum of the atomic masses of its constituent atoms. The average molar mass of air (approx. 78% nitrogen, N 2; 21% oxygen, O 2; 1% other gases) is 28.57 g/mol at standard temperature and pressure .
The density of air at sea level is about 1.2 kg/m 3 (1.2 g/L, 0.0012 g/cm 3). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law). Atmospheric density decreases as the altitude increases.
Relative density with respect to air can be obtained by =, where is the molar mass and the approximately equal sign is used because equality pertains only if 1 mol of the gas and 1 mol of air occupy the same volume at a given temperature and pressure, i.e., they are both ideal gases. Ideal behaviour is usually only seen at very low pressure.
The ideal gas equation can be rearranged to give an expression for the molar volume of an ideal gas: = = Hence, for a given temperature and pressure, the molar volume is the same for all ideal gases and is based on the gas constant: R = 8.314 462 618 153 24 m 3 ⋅Pa⋅K −1 ⋅mol −1, or about 8.205 736 608 095 96 × 10 −5 m 3 ⋅atm⋅K ...