# Physical chemistry help

A mole of air (80% Nitrogen, and 20% Oxygen by volume) at 298.15K is brought into contact with liquid water which has a vapor pressure of 3168 Pa at this temperature.

a) what is the volume of the dry air if the pressure is 1 bar?

b) what is the final volume of the air saturated with water vapor if the total pressure is maintained at 1 bar?

c) what are the mole fractions of N2, O2, and H20 in the moist air? Assume all gases are ideal

I need help setting up the problem, I have no clue on where to start. I started with PV=nRT but I don't know if thats right. At my school we do not have a tutor for this class so any help is greatful. thank you

chemisttree
Homework Helper
Gold Member
Vtot = ntot RT/Ptot

The number of moles of the system is the sum of the number of moles of each component. This can be determined if you know the pressure, temperature and volume of the system.

The sum of the partial pressures of all of the components equals the total pressure of the system. It can be determined from the ideal gas equation if you know moles, temperature and volume.

Final volume of the system is the sum of the volumes of each component. Volume can be determined from the ideal gas equation if you know moles, temperature and pressure.