$word_{count}$: 220

Raoult's law states that the partial vapour pressure of each volatile component in an ideal solution is proportional to its mole fraction: $P_A$ = $x_A$ * P_A_{std} and $P_B$ = $x_B$ * P_B_{std}. Total pressure: $P_{total}$ = $x_A$P_A_{std} + $x_B$P_B_{std} = P_B_{std} + (P_A_{std} - P_B_{std})$x_A$, which is linear in $x_A$. The vapour composition: $y_A$ = $\frac{P_A}{P_total}$ = $x_A$P_A_{std}/$P_{total}$ (Dalton's law). The more volatile component (higher $P_{std}$) is enriched in the vapour phase — this is the principle behind fractional distillation. Ideal solutions satisfy: delta_H_{mix} = 0 $\frac{no heat absorbed}{released}$, delta_V_{mix} = 0 (no volume change), and A-B interactions ≈ average of A-A and B-B. Examples: benzene + toluene, n-hexane + n-heptane, chlorobenzene + bromobenzene — all pairs with similar molecular structures. $P_{total}$ vs $x_A$ is a straight line for ideal solutions. $P_{total}$ vs $y_A$ gives a curve. On T-x and T-y diagrams, the liquid line (bubble curve) and vapour line (dew curve) enclose the two-phase region. The lever rule gives the ratio of liquid to vapour phases at any point in this region. Understanding ideal solutions provides the baseline for analysing deviations.