Let us consider a binary solution of two volatile liquids and denote the
two components as 1 and 2 When taken in a closed vessel, both the
components would evaporate and eventually an equilibrium would be
established between vapour phase and the liquid phase Let the total
vapour pressure at this stage be ptotal and p1 and p2 be the partial
vapour pressures of the two components 1 and 2 respectively These
partial pressures are related to the mole fractions x1 and x2 of the two
components 1 and 2 respectively