Ideal Solution
Definition and meaning of Ideal Solution in chemistry.
An ideal solution is a mixture in which the intermolecular forces between unlike molecules are essentially identical to those between like molecules, so the solution obeys Raoult's law across its entire range of composition.
In more detail
Because solute-solute, solvent-solvent, and solute-solvent interactions are effectively equal, mixing the components produces no enthalpy change (delta H mix = 0) and no volume change (delta V mix = 0). The only driving force for mixing is the increase in entropy from the greater number of ways molecules can be arranged, the same statistical effect seen in ideal gas mixing. Real mixtures approach ideal behavior when the components are chemically and structurally similar, since this minimizes differences in intermolecular attraction. Most real solutions show positive or negative deviations from Raoult's law when the components differ significantly in polarity or molecular size.
Key facts
| Field | Physical Chemistry |
|---|---|
| Governing Law | Raoult's Law, P_A = X_A * P_A° |
| Enthalpy of Mixing | delta H_mix = 0 |
| Volume of Mixing | delta V_mix = 0 |
A mixture of benzene and toluene behaves nearly ideally because the two molecules are similar in size, shape, and polarity, so each component's vapor pressure closely follows Raoult's law, P = X times P degree, across the full composition range.
Frequently asked questions
What causes a solution to deviate from ideal behavior?
Deviations arise when the attraction between unlike molecules is stronger or weaker than between like molecules, producing negative or positive deviations from Raoult's law, respectively.
Is an ideal solution the same concept as an ideal gas?
They are analogous but not identical: an ideal gas assumes no intermolecular forces at all, while an ideal solution assumes the forces exist but are equal between all pairs of molecules.