Raoult's Law
The partial vapour pressure of each component of an ideal solution equals its mole fraction times its pure vapour pressure.
Formula / equation
p_A = x_A p°_A
Unit
Pa
In depth
The law holds exactly for ideal solutions in which all intermolecular interactions are equivalent, and approximately for the solvent in any dilute solution. Plotting total vapour pressure against composition gives a straight line for an ideal mixture, and departures from it define non-ideality.
Examples in the real world
Benzene and toluene follow Raoult's law closely because their intermolecular forces are almost identical.