What is the composition of the vapour which is in equilibrium at `30@C` with a benzene-toluene solution with a mole fraction of benzene of (a) `0.400` and (b) `0.600`?
`P_(b)@ = 119` torr ,`P_(t)@ = 37.0` torr

Explanation

`p_(b) = 0.400 xx 119` torr = `47.6` torr
`p_(t) = 0.600 xx 37.0` torr = `22.2` torr
`p_("total") = (47.6 + 119 "torr" = 22.2) = 69.8` torr
The composition of vapour is determined by applying Dalton's law of partial pressures:
`chi_(b) = p_(b)/p_("total") = 47.6/69.8 =0.682`
`chi_(b) = 22.2/69.8 = 0.318 = 1.000 - 0.682`
Similarly, for the case of the solution in which the mole fraction of toluence is `0.400`,
`chi_(b) = 71.5/86.3 = 0.829`, `chi_(t) = 14.8/86.3 = 0.171`