RAOULT'S LAW

Hello everyone,

Today's topic is RAOULT'S LAW.

VAPOUR PRESSURE : 

When a solvent is kept in container it gets evaporated and finally equilibrium is achieved.The pressure is exerted by vapour at equilibrium condition is called Vapour Pressure.

Vapour pressure changes with the temperature of the surroundings and the nature of the liquid.    

RAOULT'S LAW OF VAPOUR PRESSURE :

CASE.1: For solution containing volatile components :  Partial pressure of a component is directly proportional to mole fraction of the components.                                                        P_A ∝ x_A

                                                PA = P_A⁰ x_A

where P_A⁰ is the vapour pressure of pure liquid component A. Similarly partial pressure of B will be

                                                 P_B ∝ x_B

                                                 P_B = P_B⁰ x_B

where P_B⁰ is the vapor pressure of pure liquid component B. Now, we will apply Dalton’s law of partial pressures. This law tells us that the total pressure ( P_total) of the solution placed in a container is the sum of partial pressures of its respective components. That is

                                                 P_total = P_A + P_B

                                              P_total = P_A⁰ x_A + P_B⁰ x_B

Also since, x_A + x_B = 1 , we can write the relation as:

                                           P_total = P_A⁰ + (P_B⁰ – P_A⁰) x_B

CASE.2: For solution containing non- volatile components: Total vapour pressure of solution is directly proportional yo mole fraction of the solvent.

                                                    P_total = P_A + P_B = P_A

                                                         P_total    = P_A⁰ x_A = P⁰ X(solvent).