Q5.34P - Chemistry: Molecular Nature Of Matter And Change

Question

Why is moist air less dense than dry air?

Step-by-Step Solution

Answer

The density of moist air is less than dry air because moist air has a lower molecular mass.

Step 1: Dry air and moist air

Dry air is the combination of approx.  $78\%$  nitrogen (molecular mass is $\text{28\hspace{0.17em}g/mol}$  ) and  $21\%$  oxygen (molecular mass is  $\text{32\hspace{0.17em}g/mol}$ ).

Moist air consist of water vapour and its molecular mass is  $\text{18\hspace{0.17em}g/mol}$ .

Therefore, the mass of moist air is very less than that of dry air.

Step 2: Density of moist air and dry air

The density is the ratio of mass to the volume.

It means that, if the mass is greater, density will be greater and vice versa.

As the mass of moist air is less than the mass of dry air.

Thus, the density of moist air is less than that of dry air.