Raoults and Henrys Laws

In the development of physical chemistry, investigations of dilute solutions have been very important. A dilute solution consists of the main constituent, the solvent, and one or more solutes, which are the diluted species. As early as in 1803 William Henry showed empirically that the vapour pressure of a solute i is proportional to the concentration of solute i  

More than 80 years later Francois Raoult demonstrated that at low concentrations of a solute, the vapour pressure of the solvent is simply 

Raoult s law is obeyed for a solvent at infinite dilution of a solute. Mathematically this implies 

A solute B obeys Henry s law at infinite dilution if the slope of the activity curve aB versus xB has a nonzero finite value when xB - 0  

The finite value of the slope when xB — 0, yB, is the activity coefficient at infinite dilution defined earlier. In terms of activity coefficients eq. (3.46) becomes 

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