Thermodynamics/Process Calculation: Partial Pressure and deviation

There are three law’s which are used to calculate pressure of a component in a mixture.

Raoult’s Law: gives the partial pressure of a component from its vapor pressure (function of temperature) by multiplying it with its mole fraction in liquid phase: p_A=x_APAv

Henry Law: gives the partial pressure of a component from its mole fraction in liquid phase multiplied by a constant (H: Henry constant) which depends on temperature and the presence of other component: p_A=x_AH_A

Dalton law: gives the partial pressure of a component from its vapor phase mole fraction multiplied by total pressure: p_A=y_AP_T

The question arises where to apply Raoult’s Law and where Henry Law. 

The difference between the two is Raoult’s law is applicable to the pure component i.e. xi close to 1, while the Henry law is applied to a very dilute component i.e. xi is close to 0.

At any concentration other than the limiting values of 0 and 1, the partial pressure of solute A will be different from the Henry Law and it shows a deviation. The positive deviation shows that the component A has more tendency to go in vapor phase. While the negative deviation shows that the component A has more tendency of being in the liquid phase.