--%>
Assignment Help - homework help

Explain vapour pressure of liquid solutions.

Liquid solutions are obtained when the solvent is liquid. The solute can be a gas, liquid or a solid. In this section we will discuss the liquid solutions containing solid or liquid solutes. In such solutions the solute may or may not be volatile. We shall limit our discussion to the binary solution of the solid in liquid and liquid in liquid. Before we discuss the properties of these solution let us study about the vapour pressure of liquid.

When a liquid is taken in a beaker covered from above at certain temperature, a part of the liquid evaporates and its vapours fill the space available to them. The vapours formed will have an inclination to change back to its liquid state by the procedure of condensation. Gradually, equilibrium will be established between liquid and vapour phases. The pressure exerted by the vapours above the liquid surface in equilibrium with the liquid surface in equilibrium with the liquid at a given temperature is called vapour pressure of the liquid.

The vapour pressure of a liquid depends on Nature of liquid

Liquid which have weak intermolecular forces, are volatile and have greater vapour pressure. For instance, dimethyl ether has higher vapour pressure than ethyl alcohol.
    
Temperature 

Vapour pressure increases with the increase in temperature. This is due to the increase in temperature through which more molecules of the liquid can go into vapour phase.

The variation of vapour pressure of a liquid with temperature is given by the Claussius Clapeyron's equation.

2181_Liquid pressure.png   where, p1 and p2 are vapour pressures at temperature T1 and T2 respectively. Δvap.H is enthalpy of vaporization of liquid and R is universal gas constant.

Vapour pressure of the solution of solids in liquids

Let us consider the addition of a small amount of non-volatile solute such as glucose, sucrose, sodium chloride etc. to the liquid (solvent such as water) to form a solution. In such a case the vapour pressure of the solution is solely due to the solvent, as the solute is non-volatile. It is found that the vapour pressure of the solution is lower than that of the pure solvent.

Explanation: the lowering of vapour pressure can be explained on the basis of the surface area of the liquid from which evaporation occurs. In the case of the solution, a part of the liquid surface is occupied by solute particles, which are non-volatile. Therefore, evaporation of the liquid will take place from a lesser surface area. In other words, the particles (or molecules) of the liquid will now have a less tendency to escape into vapour state. This shall, therefore, result in lowering of vapour pressure.

   Related Questions in Chemistry

  • Q : Diffusion Molecular View When the

    When the diffusion process is treated as the movement of particles through a solvent the diffusion coefficient can be related to the effective size of diffusing particles and the viscosity of the medium.To see how the experimental coefficients can be treat

    		•
  • Q : Illustrations of the reversible reaction

    What are the various illustrations of the reversible reaction? Explain briefly?

    		•
  • Q : Determining Mole fraction of water Can

    Can someone please help me in getting through this problem. The mole fraction of water in 20% aqueous solution of H2O2 is: (a) 77/68 (b) 68/77 (c) 20/80  (d) 80/20

    		•
  • Q : Procedure for separating the components

    Briefly describe the procedure for separating the components of the gun-powder?

    		•
  • Q : Problem on reversible and irreversible

    The second law states that  dS ≥ (dQ/T), where dS = dQ/T for a reversible process and dS > dQ/T for an irreversible process.   a. Show that since dW12 = -dW21 (dWreverse = -dWforward) for a r

    		•
  • Q : Explain Solid Compound Formation. In

    In some two component, solid liquid systems, a solid compound forms.In systems in which the components have an interaction for such other, a solid state compound of the two compounds of the two components can form.Formic acid and formaide form a solid state, one-to-one com

    		•
  • Q : Strength of dilute acid of Sulfuric acid

    Select the right answer of the question.10ml of conc.H2SO4 (18 molar) is diluted to 1 litre. The approximate strength of dilute acid could be: (a)0.18 N (b)0.09 N (c) 0.36 N (d)1800 N

    		•
  • Q : Molar concentration of Iron chloride

    Provide solution of this question. A certain aqueous solution of FeCl3 (formula mass =162) has a density of 1.1g/ml and contains 20.0% Fecl. Molar concentration of this solution is: (a) .028 (b) 0.163 (c) 1.27 (d) 1.47

    		•
  • Q : From where the tin is obtained From

    From where the tin is obtained? Briefly illustrate it.

    		•
  • Q : What are Vander Waal's Radii? Vander

    Vander Waal's radii can be assigned to the atoms of molecules on the basis of the closeness of approach of these atoms in crystalline substances. Diffraction studies of crystals give information about hoe molecules can approach each other and can pack

    		•