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