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Air density, like air pressure, decreases with increasing altitude. It also changes with variations in atmospheric pressure, temperature and humidity. At 101.325 kPa (abs) and 20 °C (68 °F), air has a density of approximately 1.204 kg/m 3 (0.0752 lb/cu ft), according to the International Standard Atmosphere (ISA).
1 Nm 3 of any gas (measured at 0 °C and 1 atmosphere of absolute pressure) equals 37.326 scf of that gas (measured at 60 °F and 1 atmosphere of absolute pressure). 1 kmol of any ideal gas equals 22.414 Nm 3 of that gas at 0 °C and 1 atmosphere of absolute pressure ... and 1 lbmol of any ideal gas equals 379.482 scf of that gas at 60 °F and ...
The volume of air displaced at experimental temperature and pressure is calculated. Then volume of air displaced at standard temperature and pressure is calculated. Using this, mass of air displaced at 2.24 × 10 −2 m 3 of vapour at STP is calculated. This value represents the molecular mass of the substance.
Only certain lighter than air gases are suitable as lifting gases. Dry air has a density of about 1.29 g/L (gram per liter) at standard conditions for temperature and pressure (STP) and an average molecular mass of 28.97 g/mol, [1] and so lighter-than-air gases have a density lower than this.
The table below displays densities and specific volumes for various common substances that may be useful. The values were recorded at standard temperature and pressure, which is defined as air at 0 °C (273.15 K, 32 °F) and 1 atm (101.325 kN/m 2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr). [4]
= specific heat of air at constant pressure, [MJ kg −1 °C −1], = ratio molecular weight of water vapor/dry air = 0.622. Both and are constants. Since atmospheric pressure, P, depends upon altitude, so does .
Where ρ is mass density, M is average molecular weight, P is pressure, T is temperature, and R is the ideal gas constant. The gas is held in place by so-called "hydrostatic" forces. That is to say, for a particular layer of gas at some altitude: the downward (towards the planet) force of its weight, the downward force exerted by pressure in ...
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 .