Real versus Ideal Solution

In Section 1.13.3, we used the difference between the properties of a real fluid and an ideal gas to describe the effect of intermolecuiar forces on the thermodynamic properties of the fluid. Here we use the difference between real and ideal solution behavior of a fluid, at the same T, P and compositions, to describe the effect of the differences in  

The comparison is done at the same temperature, pressure, and composition, and the resulting difference is called the excess Junction (Chapter 11)  

Excess Function = Real solution property (7, P, x) -Ideal solution property (T, P, x) 

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For an ideal solution, then, a plot of n,ic versus c should be a straight line at constant temperature. But, as you might expect, there is a variation with concentration (Figure 12-7). Just as with real gases, however, the data can be fit to the polynomial we call a virial equation. But, what do we do about polymers that have a distribution of molecular weights ... 

For ideal solutions the ratio ly p/c (called the reduced viscosity) is independent of solution concentration. In real solutions the reduced viscosity varies with concentration owing to molecular interactions and it is usual to extrapolate plots of j p/c versus c to zero concentration. The extrapolated value is called the intrinsic viscosity [jy]. 

Figure 9.7-3 Solute fugacity in real and ideal Henry s law solutions, (ri) Solute fugacity versus mole fraction. (b) Solute fugacity versus molality.

A Gaussian bandshape results when the partition coefficient, K (= Cs/Cm), is independent of the concentration of solute on the column. In real columns, K changes as the concentration of solute increases, and bandshapes are skewed.10 A graph of Cs versus Cm (at a given temperature) is called an isotherm. Three common isotherms and their resulting bandshapes are shown in Figure 23-20. The center isotherm is the ideal one, leading to a symmetric peak. 

Figure 39.2 The graphs show plots of (a) /r(i)

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