# Raoult's law

Raoult's law states that the vapour pressure of an ideal solution of $N$ components is:

$P_v = \sum_{i=1}^{N} X_i P^*_{v,i}$

where $X_i$ is the molar fraction of component $i$, and $P^*_{v,i}$ is the vapour pressure of pure $i$. More generally, Raoult's law describes the partial pressure of component $A$ in the vapour coexisting with a liquid mixture as:

$P_A = X_A P^*_{v,A}$.

This law is obeyed for all components of an ideal solution, and is also obeyed for the solvent of an ideal dilute solution. The solute's partial pressure of such solutions then obey Henry's law. Ideal dilute solutions describe the limiting behaviour of a mixture of infinite dilution. Therefore, all solutions in the limit of infinite dilution obey Raoult's law, i.e.:

$\lim_{X_A \rightarrow 1} P_A = X_A P^*_{v,A}$.