Solutions, perfect total vapour pressures

The case of benzene-toluene mixture discussed above is an example of a solution which follows Raoult s law sufficiently closely. Solutions which obey Raoult s law are called ideal or perfect solutions. According to this law, the total vapour pressure, P, of an ideal solution gets expressed by the relation ... 

Fig. 21.1 shows the partial vapour pressures and the total pressure of a perfect solution as a function of composition. In the case of a binary solution (21.8) may be written... 

Fig. 21.1. Total and partial vapour pressure of a perfect solution at constant T.

Greater physical insight into a particular problem may often be obtained by making direct application, not of the phase rule itself, but of the conditions of equilibrium on which it is based. As an example consider the system discussed under case (c) above. Let T and p be the temperature and total pressure respectively and let partial pressures in the vapour and let etc., be the mole fractions in the liquid phase. If the gas phase may be assumed for simplicity to be a perfect mixture and if the liquid phase is an ideal solution, then the eight variables are related by the following six equations Pa+Pb+Pc=P. 

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See also in sourсe #XX -- [ ]

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