This question addresses the two piston-cylinder assemblies depicted on the left of Figure 1.8 that illustrate the concept of saturation pressure. The piston on the right is at twice the pressure of the system on the left; however, if you count molecules of species a, there are less than twice the number on the right (i.e., the number does not increase directly proportional to temperature). Is this a mistake? Explain.

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Saturation Pressure: Psat is defined for a system of pure a P = psat a m T=T Saturated vapor a a a a a Saturated liquid a a m m T = T >T Saturated vapor a a a a a a a a a Saturated liquid a a 1 Vapor Pressure: pa is defined for a vapor mixture of a and b P = P+ Pb = Pat + Pb T=T b a E m Saturated vapor b a a a b b b a a b a b b m a m m b ba T=T > T Saturated vapor a ba a a ba a b a Liquid a a a ba Liquid a 1. The case depicted assumes ideal gas behavior and that species b does not condense into the liquid phase: Figure 1.8 Graphical representation of the saturation pressure of pure a and the vapor pres- sure of a in a mixture of a and b. Two temperatures, T and T are shown.