Activity from Measurements of Vapor Pressure

If the vapor pressure of a substance in solution is sufficiently great to be determined experimentally, the activity can be calculated directly. As the standard state differs for the solvent and solute, each must be considered separately. 

The activity of the solvent is related directly to the vapor pressure when the vapor is an ideal gas. As the pure solvent is the standard state, the chemical potential p,i of the solvent in any solution is given by the expression [Equation (16.1)] 

Chemical Thermodynamics Basic Concepts and Methods, Seventh Edition. By Irving M. Klotz and Robert M. Rosenberg 

DETERMINATION OF NONELECTROLYTE ACTIVITIES AND EXCESS GIBBS FUNCTIONS 

The chemical potential of the solvent in the liquid phase in equilibrium with its vapor is equal to the chemical potential of the solvent vapor. Thus, 

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