For an ideal solution, the partial vapor pressure of the volatile solvent above the liquid is proportional to its mole fraction in the liquid phase — Raoult's Law:
P_solvent = x_solvent · P°_solvent
x_solvent = 1 − x_solute
ΔP = P°_solvent − P_solvent = x_solute · P°_solvent
Physically, a non-volatile solute occupies a fraction xsolute of the liquid surface, blocking that fraction of solvent molecules from escaping into the vapor phase per unit time — this simulator renders that surface directly: solute spheres (green) sit among solvent spheres (blue), and only solvent molecules that reach an unblocked surface site evaporate. The pure-solvent vapor pressure P°(T) itself grows with temperature following the Clausius-Clapeyron relation:
ln(P°) = ln(P°_ref) − (ΔH_vap/R)·(1/T − 1/T_ref)
- xsolute slider — raises the fraction of surface sites occupied by solute, lowering P linearly (Raoult's Law) and visibly thinning the vapor cloud above the liquid.
- Temperature slider — rescales P° via Clausius-Clapeyron, so both P° and P rise together while the ratio P/P° = x_solvent stays fixed — this ratio is the pure colligative signature of the law, independent of temperature.
- +Deviation — adds a small positive deviation from ideality (solute-solvent interactions weaker than solvent-solvent), so P sits slightly above the ideal Raoult's-Law line, as real solutions like ethanol-water often do.
Real-world relevance: Raoult's Law underlies distillation, boiling-point elevation, freezing-point depression, and how antifreeze or salt lowers a liquid's tendency to evaporate — the same x·P° relation this simulator visualizes molecule by molecule.