Solutions - Ideal and Non-ideal Solutions

Ideal Solutions: These are solutions that obey Raoult's law over the entire range of concentration. For an ideal solution formed by components $A$ and $B$, the intermolecular attractive forces between $A-A$ and $B-B$ are nearly equal to those between $A-B$.

Thermodynamics of Ideal Solutions: For these solutions, the enthalpy of mixing is zero, i.e., $\Delta_{mix}H = 0$, and the volume of mixing is zero, i.e., $\Delta_{mix}V = 0$.

Non-Ideal Solutions (Positive Deviation): Occurs when $A-B$ interactions are weaker than $A-A$ or $B-B$ interactions. In this case, $P_A > P_A^0 \chi_A$ and $P_B > P_B^0 \chi_B$. These solutions show $\Delta_{mix}H > 0$ and $\Delta_{mix}V > 0$. Example: Ethanol and Acetone.

Non-Ideal Solutions (Negative Deviation): Occurs when $A-B$ interactions are stronger than $A-A$ or $B-B$ interactions. In this case, $P_A < P_A^0 \chi_A$ and $P_B < P_B^0 \chi_B$. These solutions show $\Delta_{mix}H < 0$ and $\Delta_{mix}V < 0$. Example: Chloroform and Acetone.

Azeotropes: These are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature. Minimum boiling azeotropes are formed by solutions showing large positive deviation, while maximum boiling azeotropes are formed by solutions showing large negative deviation.