Ideal solutions

Non-ideal solutions

      Positive deviation from Raoult's law

Negative deviation from Raoult's law

1. Obey Raoult's law at every range of concentration.

1. Do not obey Raoult's law.

1.             Do not obey Raoult's law.

2. ΔH_mix = 0; neither heat is evolved nor    absorbed during dissolution. 

2.  ΔH_mix > 0 Endothermic dissolution; heat is absorbed. 

2.  ΔH_mix < 0  Exothermic dissolution; heat is evolved. 

3.  ΔV_mix = 0; total volume of solution is equal to sum of volumes of the components.

3.  ΔV_mix > 0 Volume is increased after dissolution.

3.  ΔV_mix < 0  Volume is decreased during dissolution.

4.    i.e.,

4.                

4.               

5. A-A, A-B, B-B interactions should be same, i.e., 'A' and 'B' are identical in shape, size and character.

5. A-B attractive force should be weaker than A-A and B-B attractive forces. 'A' and 'B' have different shape, size and character.  

5. A-B attractive force should be greater than A-A and B-B attractive forces. 'A' and 'B' have different shape, size and character.

6. Escaping tendency of 'A' and 'B' should be same in pure liquids and in the solution.

6. 'A' and 'B' escape easily showing higher vapour pressure than the expected value.

6. Escaping tendency of both components 'A' and 'B' is lowered showing lower vapour pressure than expected ideally.

     Examples:

     Dilute solutions;

     benzene + toluene:

     n-hexane + n-heptane;

     chlorobenzene + bromobenzene;

     ethyl bromide + ethyl iodide;

     n-butyl chloride + n-butyl bromide

     Examples:

     Acetone +ethanol

     acetone +CS₂:

     water + methanol;

     water + ethanol;

     CCl4 + toluene;

     CCl₄ + CHCl₃;

     acetone + benzene;

     CCl₄+CH₃OH;

     cyclohexane + ethanol

     Examples:

     Acetone + aniline;

     acetone + chloroform;

     CH₃OH+CH₃COOH;

     H₂O+HNO₃

     chloroform + diethyl ether;

     water + HCl;

     acetic acid + pyridine;

     chloroform + benzene