solution, irrespective of its nature. For example, decrease in the vapour pressure of water by adding . mol of sucrose to one kg of water is nearly similar to that produced by adding . mol of urea to the same quantity of water at the same temperature.
Raoult’s law in its general form can be stated as, for any solution the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction . In a binary solution, let us denote the solvent by and solute by . When the solute is non-volatile, only the solvent molecules are present in vapour phase and contribute to vapour pressure. Let p be .
. Raoult’s Law as a special case of Henry’s Law . . Vapour Pressure of Solutions of Solids in Liquids Fig.
. : Decrease in the vapour pressure of the solvent on account of the presence of solute in the solvent (a) evaporation of the molecules of the solvent from its surface is denoted by , (b) in a solution, solute particles have been denoted by and they also occupy part of the surface area. the vapour pressure of the solvent, x be its mole fraction, p i be its vapour pressure in the pure state. Then according to Raoult’s law p µ x and p = x ( .
) The proportionality constant is equal to the vapour pressure of pure solvent, p . A plot between the vapour pressure and the mole fraction of the solvent is linear (Fig. . ).
Liquid-liquid solutions can be classified into ideal and non-ideal solutions on the basis of Raoult’s law. The solutions which obey Raoult’s law over the entire range of concentration are known as ideal solutions . The ideal solutions have two other important properties. The enthalpy of mixing of the pure components to form the solution is zero and the volume of mixing is also zero, i.e., D mix H = , D mix V = ( .
) It means that no heat is absorbed or evolved when the components