In: Chemistry
Show that the density of moist air is less than that of dry air both at the same temperature and pressure. Does this difference between the densities of moist air and dry air, for given pressure and temperautre have any relevance to atmospheric processes?
Density of air will vary as the temperature and moisture content in the air varies
The amount of water vapor in the air also effects the density. Water vapor is a relatively light gas when compared to diatomic Oxygen and diatomic Nitrogen. Thus, when water vapor increases, the amount of Oxygen and Nitrogen decrease per unit volume and thus density decreases because mass is decreasing.
The two most abundant elements in the troposphere are Oxygen and
Nitrogen. Oxygen has an 16 atomic unit mass while Nitrogen has a 14
atomic units mass. Since both these elements are diatomic in the
troposphere (O2 and N2), the atomic mass of diatomic Oxygen is 32
and the diatomic mass of Nitrogen is 28.
Water vapor (H2O) is composed of one Oxygen atom and two Hydrogen
atoms. Hydrogen is the lightest element at 1 atomic unit while
Oxygen is 16 atomic units. Thus the water vapor atom has an atomic
mass of 1 + 1 + 16 = 18 atomic units. At 18 atomic units, water
vapor is lighter than diatomic Oxygen (32 units) and diatomic
Nitrogen (28 units). Thus at a constant temperature, the more water
vapor that displaces the other gases, the less dense that air will
become.