Question

The relative humidity of air is equal to the ratio of the partial pressure of water in the air to the equilibrium vapor pressure of water at the same temperature. If the relative humidity of the air is 30.% and its temperature is 23°C, how many molecules of water are present in a room measuring 13 m ✕ 6.5 m ✕ 6.0 m? (The vapor pressure of water at 23°C is 21.07 torr.)

Ii believe we have to use the Clausius-
Clapeyron Equation

Answer 1

I don't know how the Clausius-Clapeyron equation fits. I would do this.
0.3 = pH2O/21.07 torr
Solve for pH2O in torr and convert to atm.
Then find the volume of the room, convert to L, then use PV = nRT. Solve for n = number of mols.
Then remember 1 mole of anything contains 6.02E23 molecules.