Phase change boiling point

In general, at the phase interface the components with the higher boiling points preferentially change from vapour to condensate. As a result of this the vapour mixture at the phase interface contains more of the more volatile component than at a large distance away from it. A concentration profile like that presented in Fig. 4.19d develops. The concentration of the more volatile component increases towards the phase interface. At steady-state, the molecules of the more volatile... 

If the fluid is at its boiling point, then volume is generated through the phase change that occurs upon vaporization ... 

Boiling point The temperature at which the vapor pressure of a liquid is equal to the external pressure, and the liquid changes phase into the vapor state. 

Just as the solid/liquid phase equilibria in the systems HX/H2O show several points of interest, so too do the liquid/gas phase equilibria. When dilute aqueous solutions of HX are heated to boiling the concentration of HX in the vapour is less than that in the liquid phase, so that the liquid becomes progressively more concentrated and the bp progressively rises until a point is reached at which the liquid has the same composition as the gas phase so that it boils without change in composition and at constant temperature. This mixture is called an azeotrope (Greek a, without zein, to boil rpo7tr, trope, change). 

Table 11-4 lists values of A, A / vap, melting points, and boiling points for different chemical substances. Example provides practice in using enthalpies of phase changes. 

Phase diagrams are constructed by measuring the temperatures and pressures at which phase changes occur. Approximate phase diagrams such as those shown in Figures 11-39 and 11-40 can be constmcted from the triple point, normal melting point, and normal boiling point of a substance. Example illustrates this procedure. 

Elevation of boiling point and depression of freezing point of the solution. Within certain limits, the change in temperature of these phase transitions obeys the eqnation... 

This example is based on the model description of Sec. 3.3.4, and involves a multicomponent, semi-batch system, with both heating and boiling periods. The compositions and boiling point temperatures will change with time. The water phase will accumulate in the boiler. The system simulated is based on a mixture of n-octane and n-decane, which for simplicity will be assumed to be ideal but which has been simulated using detailed activity coefficient relations by Prenosil (1976). 

What is unique about these three properties of water boiling point, specific heat capacity, and density change over phase change ... 

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