Question

why Raoult's law is considered special case of henry's law but not vice versa????

Answer 1

According to Raoult’s law, the vapour pressure of a volatile component in a given solution is given by pi = xi pi0. In the solution of a gas in a liquid, one of the components is so volatile that it exists as a gas and we have already seen that its solubility is given by Henry’s law which states that

p = KH x.

If we compare the equations for Raoult’s law and Henry’s law, it can be seen that the partial pressure of the volatile component or gas is directly proportional to its mole fraction in solution. Only the proportionality constant KHdiffers from p10. Thus, Raoult’s law becomes a special case of Henry’s law in which KHbecomes equal to p10.