In Class 12 Chemistry (Solutions chapter), liquid-liquid solutions are broadly classified into two categories based on how they obey Raoult's Law: Ideal Solutions and Non-Ideal Solutions.
Ideal Solution: Obeys Raoult's Law, ΔH=0, ΔV=0.
Non-Ideal Solution: Disobeys Raoult's Law, ΔH≠0, ΔV≠0.
Positive Deviation: Mixture forces are weaker (vapor pressure increases).
Negative Deviation: Mixture forces are stronger (vapor pressure decreases).
An ideal solution is one that strictly obeys Raoult's Law at all concentrations and temperatures.
A non-ideal solution does not obey Raoult's Law.
| Property | Ideal Solution | Non-Ideal Solution |
|---|---|---|
| Raoult's Law | Obeys strictly | Does not obey |
| ΔH (Enthalpy of mix) | Zero | Not Zero (Endo/Exothermic) |
| ΔV (Volume of mix) | Zero | Not Zero (Expands/Contracts) |
| Interactions | A-B = A-A & B-B | A-B ≠ A-A & B-B |
An ideal solution is a mixture that exactly obeys Raoult's Law at all concentrations. When mixed, there is no change in volume and no heat is released or absorbed.
Ideal solutions obey Raoult's Law (ΔH=0, ΔV=0) because solute-solvent interactions are identical to pure states. Non-ideal solutions do not obey Raoult's Law (ΔH≠0, ΔV≠0) because the new interactions are either stronger or weaker.
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