Vapor-Pressure P-x Diagrams Raoult and Henry Limits

1 Vapor-Pressure (P-x) Diagrams Raoult and Henry Limits 

Let us now consider the general P-x dependence (vapor-pressure curve) of the binary A/B solution under fixed isothermal conditions (e.g., T = 25°C), with 

As indicated, we often drop the subscript B on the concentration variable x, with the understanding that x ranges from 0 (pure solvent A) to 1 (pure solute B) in the P-x diagram. Initially, we focus on x = xhq = Xsq, the concentration of the liquid phase, in accord with the usual convention for labeling solution concentration. 

We first define the concept of an ideal solution. This is the ultrasimplified limiting case in which the partial pressure of each component is simply proportional to its concentration in the liquid, 

The dotted lines represent the component partial pressures (7.45a, b) and the heavy solid line the total vapor pressure (7.45c). 

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