--%>
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 : What is Henry law constant and its

    1. The units of Henry Law constant are same as those of pressure, i.e. torr or h bar. 2. Different gases have dissimilar values of Henry law constant. The values of KH for some gases in water are given in tabl

    		•
  • Q : HCl is an acid or a base Illustrate is

    Illustrate is HCl an acid or a base ?

    		•
  • Q : Molarity 20mol of hcl solution requires

    20mol of hcl solution requires 19.85ml of 0.01 M NAOH solution for complete neutralisation. the molarity of hcl solution

    		•
  • Q : Organic and inorganic substances living

    living beings are made up of organic and inorganic substances.according to their complexity of their molecules how can ach of these substances be classified?

    		•
  • Q : Amines arrange in decreasing order of

    arrange in decreasing order of basicity pi pyridine,pyridine,pyrrole, morphine

    		•
  • Q : Hydroxide is highly insoluble in

     : 1) Chromium(III) hydroxide is highly insoluble in distilled water but dissolves readily in either acidic or basic solution. Briefly explain why the compound can dissolve in acidic or in basic but not in neutral solution. Write appropriate equations to

    		•
  • Q : Value of molar solution Select the

    Select the right answer of the question. Molar solution contains: (a)1000g of solute (b)1000g of solvent (c)1 litre of solvent (d)1 litre of solution

    		•
  • Q : Explain Photoelectron Spectroscopy. The

    The energies of both the outer and inner orbitals of atoms and molecules can be determined by photoelectron spectroscopy.Energy changes of the outermost or highest energy electron of molecules were dealt with here in a different passion. The energies of ot

    		•
  • Q : Molality of Sulfuric acid Choose the

    Choose the right answer from following. The molality of 90% H2SO4 solution is: [density=1.8 gm/ml]  (a)1.8 (b) 48.4 (c) 9.18 (d) 94.6

    		•
  • Q : Solution problem What is the correct

    What is the correct answer. To made a solution of concentration of 0.03 g/ml of AgNO3, what quantity of AgNO3 must be added in 60 ml of solution: (a) 1.8  (b) 0.8  (c) 0.18  (d) None of these

    		•