Question

Using Raoult’s law or Henry’s law for each substance (whichever one you think appropriate),
calculate the pressure and gas-phase composition (mole fractions) in a system containing a liquid that
is 0.3 mole% N2 and 99.7 mole% water in equilibrium with nitrogen gas and water vapor at 80°C.

Answer 1

Given liquid that is 0.3% N2 and 99.7% water

So Xa = 0.003

Xb = 0.997

Given 80 C

Pb of water = 354.70 mm Hg

Pa of Nitrogen = 734456.25 mm of Hg

Total pressure = 0.003 x 734456.25 + 0.997 xx 354.70

Total pressure = 2557.00 mm of Hg

total pressure P = 2557/760 atm

total pressure P = 3.36 atm

ya = XaPa/P

= 0.003 x 734456.25/ 2557

= 0.8617

yb = Xb Pb /P

=0.997 x 354.70/ 2557

= 0.1383

mole fraction of nitrogen and water in vapour phase are 0.8617 and 0.1383