Question

A stream of water vapor and air has a dew point of 60C. If the total pressure is 760 mm
of Hg, calculate the mole fraction of oxygen in the stream.

Answer 1

the actual vapor pressure (p) can be

calculated using the formula listed below:

p= $6.11*10^{(7.5*T_d)/(237.3+T_d)}$

where T_d is dew point and unit of p is millibar

so p at dew point is

p= $6.11*10^{7.5*60/(237.3+60)}$

so p = 199.3 milli bar

and 1 millibar = 0.75 mm Hg

so p will be 149.5 mm Hg

so mole fraction will be p/P_o

where P_o = 760 mm Hg

so mole fraction = 149.5/760 = 0.196

this is the mole fraction of water vapour.

mole fraction of oxygen = 1-0.196 = 0.804