For a binary solution of two volatile liquids 1 and 2, Raoult's law gives the partial vapour pressure of component 1 as:

1. Raoult's law: the partial vapour pressure of each component is proportional to its mole fraction in solution. 2. For component 1, $p_1 = p_1^0 x_1$, where $p_1^0$ is the vapour pressure of pure component 1. 3. The mole fraction used is that of the same component (x1), not the other component. _Source: syllabus Chemistry Ch 1 "Solutions", p.9_