When do you use Henry's law and when do you use Raoult's law?
Henry's law gives a relationship between the solubility of gases in liquids and their corresponding pressure above the solution. It is given by:
Therefore, the solubility of the gas is proportional to its pressure above the liquid. When the pressure increases, the solubility increases and vice versa.
Henry's law and Raoult's law generally are associated with the vapor pressures of the pure solution, of the solution with stuff in it, and of the mole fraction of stuff in the would-be pure solution.
- Henry's law works best at low concentration of the solute (close to
- Raoult's law works best at non-low concentration of the solute (
#10 - 50%#or so).
This is all in the context of a liquid-vapor equilibrium, i.e. the process of vaporization.
For ideal binary mixtures, it helps to compare Henry's law with Raoult's law.
For Raoult's law, the vapor pressure
#\mathbf(P_j = chi_jP_j^"*")#
#color(blue)(lim_(chi_j->1) (P_j)/(chi_j) = P_j^"*")#
For Henry's law, the vapor pressure
#\mathbf(P_j = chi_jk_(H,j))#
#color(blue)(lim_(chi_j->0) (P_j)/(chi_j) = k_(H,j))#
Therefore, a low mole fraction