Ideal solution and non ideal solution

ideal and non ideal solutions are well explained in these slides.

1. Ideal solution and non ideal solution with their deviations by: S aloni G oyal Himanshi M udgil

2. Before we start

3. Ideal gases It is a gas  composed of many randomly moving point particles that do not interact except when they collide elastically.  RAOULTS LAW PV= nRT a gas behaves more like an ideal gas at higher temperature and lower  pressure  potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them .

4. The ideal gas model tends to fail at lower temperatures or higher pressures, when intermolecular forces and molecular size become important. It also fails for most heavy gases, such as many  refrigerants  and for gases with strong intermolecular forces, notably water vapour.

5. Ideal solutions An ideal solution is that solution that follows raoults law under all standard temp. and conc. It satisfy that Δ V mixing =0 ΔH MIXING =0 we can also say that it is the solution of two components A and B in which the A---B interactions are of same magnitude as A---A and B----B interaction Only solutions with low conc of solute behave ideally. Ex. benzene+toluene chlorobenzene + bromobenzene

6. Non -ideal solutions The solution which do not follow raoults law. ΔV mixing = 0 and Δ H mixing = 0 It is the solution in which solute and solvent molecules interact with one another with a different force than forces of interaction between the molecules of the pure compounds. Ex: S ulphuric acid(solute) and water(solvent) the amount of heat is evolved is large and thus change in volume is also seen .

7. deviations + ve deviation: In mixtures showing a positive deviation from Raoult's Law, the vapour pressure of the mixture is always higher than you would expect from an ideal mixture.

8. The deviation can be small - in which case, the straight line in the last graph turns into a slight curve. Notice that the highest vapour pressure anywhere is still the vapour pressure of pure A. Cases like this, where the deviation is small, behave just like ideal mixtures as But some liquid mixtures have very large positive deviations from Raoult's Law, and in these cases, the curve becomes very distorted .

9. mixtures over a range of compositions have higher vapour pressures than either pure liquid. The maximum vapour pressure is no longer that of one of the pure liquids .

10. Explaining the deviations The fact that the vapour pressure is higher than ideal in these mixtures means that molecules are breaking away more easily than they do in the pure liquids. That is because the intermolecular forces between molecules of A and B are less than they are in the pure liquids. We can see that when we mix the liquids. Less heat is evolved when the new attractions are set up than was absorbed to break the original ones. Heat will therefore be absorbed when the liquids mix. The enthalpy change of mixing is endothermic. The classic example of a mixture of this kind is ethanol and water. This produces a highly distorted curve with a maximum vapour pressure for a mixture containing 95.6% of ethanol by mass.

11. - ve deviations In exactly the same way, you can have mixtures with vapour pressures which are less than would be expected by Raoult's Law. In some cases, the deviations are small, but in others they are much greater giving a minimum value for vapour pressure lower than that of either pure component.

12. Explaining the deviations These are cases where the molecules break away from the mixture less easily than they do from the pure liquids. New stronger forces must exist in the mixture than in the original liquids. we can recognise this happening because heat is evolved when we mix the liquids - more heat is given out when the new stronger bonds are made than was used in breaking the original weaker ones. this involve actual reaction between the two liquids. example of a major negative deviation that we are going to look at is a mixture of nitric acid and water. These two covalent molecules react to give hydroxonium ions and nitrate ions. You now have strong ionic attractions involved.

13. THANKYOU