ESS55
Prof. Jin-Yi Yu
Applications of the Gas law
qQuestion: Calculate the density of water vapor which exerts a pressure of 9 mb at 20°C.
Answer:
Use the ideal gas law:       Pv= rRvT
                    and   Pv = 9 mb = 900 Pa (a SI unit)
                             Rv = R* / Mv = 461 J deg-1 kg-1
                             T = 273 + 20 (°C) = 293 K.
So we know the density of water vapor is:
        r = Pv/ (RvT) = 900 / (461*293) = 6.67 x 10-3 kg m-3
(from Atmospheric Sciences: An introductory Survey)