Molecular weights of gases

Italian chemist and physicist Amadeo Avogadro (1776-1856) proposed a correct molecular explanation for Gay-Lussac s law of combining volumes. His work provided a simple way to determine atomic weights and molecular weights of gases. 

The deviations from the mean value 22-412 are very insignificant, and are probably due to unavoidable experimental errors, above all to the uncertainty in the molecular weight on which the calculation of pv is based. For this reason it has been suggested of late to use the values of pv at zero pressure for the determination of the molecular weights of gases. If pv is the limiting value of pv for 1 gr. of the gas, and M its molecular... 

The standard entropies of monatomic gases are largely determined by the translational partition function, and since dris involves the logarithm of the molecular weight of the gas, it is not surprising that the entropy, which is related to tire translational partition function by the Sackur-Tetrode equation,... 

Concentration The amount of a substance present in a given volume of a gas or liquid, in parts per million (ppm) or jLg m . In the case of gases, the ppm is proportional to the molecular concentration, hence the relationship between ppm and pg m " depends on the molecular weight of the gas concerned. 

Tlic density (p) of a substance is tlic ratio of its mass to its volume and may be expressed in units of pounds per cubic foot (Ib/ft ) or kilograms per cubic meter (kg/nv ). For solids, density can be determined easily by placing a known mass of the substance in a liquid and measuring tlie displaced volume. The density of a liquid can be measured by weighing a known volume of the liquid in a gradmitcd cylinder. For gases, tlie ideal gas law (to be discussed in Section 4.6) can be used to calculate tlie density from tlie temperature, pressure, and molecular weight of tlie gas. 

Va = molecular volume for component A, diffusing gas Vg = molecular volume for component B, diffused gas (See chapter on Packed Towers, Volume 2, 3rd Ed. for further discussion.) Compute from atomic volumes kj = diffusivity, fL/hr p/ = total pressure, atm Tg = absolute temperature, ° Kelvin Ma and Mg = molecular weights of the gases... 

These results and many similar ones led Avo-gadro to propose his famous hypothesis, as discussed in Section 2-2.3. The hypothesis states that equal volumes of gases contain equal numbers of molecules (at the same temperature and pressure). Therefore, the molecular weight of a gas... 

A gas well contains hydrocarbon gases with an average molecular weight of 24, which can be assumed to be an ideal gas with a specific heat ratio of 1.3. The pressure and temperature at the top of the well are 250 psig and 70°F, respectively. The gas is being produced at a slow rate, so conditions in the well can be considered to be isentropic. 

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