2.2.2 Vapor-pressure lowering If the solute is nonvolatile p. is the total vapor pressure of the solution. Because the mole fraction of solvent in a solution is always less than that for the pure solvent; the vapor pressure is lowered2.2.2 Vapor-pressure lowering If the solute is nonvolatile, pA is the total vapor pressure of the solution. Because the mole fraction of solvent in a solution is always less than that for the pure solvent; the vapor pressure is lowered