Vapor Pressure Methods

Vapor pressure measurement provides a simple method for determination of activity of any component that is directly related with its partial pressure. If pi is the partial pressure of the component, i in the solution and \( {p}_i^o \) is the partial pressure of i in pure state at the same temperature, the ratio \( {p}_i/{p}_i^o \) will give activity, ai of the component in the solution. The activities are related to the equilibrium constant that can be used to calculate free energy of a reaction. The experimental methods available for vapor pressure measurement can be broadly classified into three main groups: static, dynamic and effusion. Isoteniscope technique under direct static, and vapor weight, thermal conductivity, vapor ionization, tracer, optical absorption technique, phase change and isopiestic methods under indirect static categories have been discussed. Under dynamic methods, boiling point and transpiration methods have been covered. Knudsen effusion and torsion effusion cell have been focused under effusion methods.