Aerospace engineers sometimes write the gas law in terms of the mass of the gas rather than

Question:

Aerospace engineers sometimes write the gas law in terms of the mass of the gas rather than the number of moles:

In such a formulation, the molar mass of the gas must be incorporated into the value of the gas constant, which means that the gas constant would differ from one gas to another. (We have written the gas constant here as R_specific to emphasize this point. Many engineering texts use different notations to distinguish between the universal and specific gas constants.)

(a) Suggest a reason why this approach might be particularly attractive in aerospace engineering.

(b) Assume that the mole fractions of O₂ and N₂ in air are 0.21 and 0.79, respectively. Calculate the average molar mass of air (i.e., the mass of one mole of air).

(c) Use your result from part (b) to determine the value of R_specific for air, and express it in SI units of m² s^-2 K^-1