Phase diagram pure substances

Fig. 2. PT diagram for a pure substance that expands on melting (not to scale). For a substance that contracts on melting, eg, water, the fusion curve. A, has a negative slope point / is a triple state point c is the gas—Hquid critical state (—) are phase boundaries representing states of two-phase equiUbrium ...

Figure 2-78. Typical phase diagram for a pure substance showing P-V-T surface and its projections [60],...

Vapor—Liquid Systems. The vapor-liquid region of a pure substance is contained within the phase or saturation envelope on a P-V diagram (see Figure 2-80), A vapor, whether it exists alone or in a mixture of gases, is said to be saturated if its partial pressure (P.) equals its equilibrium vapor pressure (P, ) at the system temperature T. This temperature is called the saturation temperature or dew point T ... 

Figure 2-80. Typical P-V diagram for a pure substance showing isotherms and saturation (phases) envelope.

Quality of a Wet Vapor, in the vapor-liquid region of a pure substance, the composition of a two-phase system (at given T and P) varies from pure saturated liquid at the bubble jjoint M to pure saturated vapor at the dew point N along the line MQN on the P- V diagram (Figure 2-80). For a wet vapor represented by an intermediate... 

Chapters 7 to 9 apply the thermodynamic relationships to mixtures, to phase equilibria, and to chemical equilibrium. In Chapter 7, both nonelectrolyte and electrolyte solutions are described, including the properties of ideal mixtures. The Debye-Hiickel theory is developed and applied to the electrolyte solutions. Thermal properties and osmotic pressure are also described. In Chapter 8, the principles of phase equilibria of pure substances and of mixtures are presented. The phase rule, Clapeyron equation, and phase diagrams are used extensively in the description of representative systems. Chapter 9 uses thermodynamics to describe chemical equilibrium. The equilibrium constant and its relationship to pressure, temperature, and activity is developed, as are the basic equations that apply to electrochemical cells. Examples are given that demonstrate the use of thermodynamics in predicting equilibrium conditions and cell voltages. 

The schematic phase behaviour of C02 depicted in Figure 8.1 is only valid for the pure compound. The phase behaviour of mixtures is much more complex [6], being a function of composition, and the actual phase diagram can vary considerably even for seemingly similar components. Reaction systems contain at least three substances (substrate, product and catalyst), but in most cases more components are present and a... 

Most hydrophobic substances have low solubilities in water, and in the case of liquids, water is also sparingly soluble in the pure substance. Some substances such as butanols and chlorophenols display relatively high mutual solubilities. As temperature increases, these mutual solubilities increase until a point of total miscibility is reached at a critical solution temperature. Above this temperature, no mutual solubilities exist. A simple plot of solubility versus temperature thus ends at this critical point. At low temperatures near freezing, the phase diagram also become complex. Example of such systems have been reported for sec-butyl alcohol (2-butanol) by Ochi et al. (1996) and for chlorophenols by Jaoui et al. (1999). 

Freeze drying is mostly done with water as solvent. Fig. 1.1 sows the phase diagram of water and the area in which this transfer from solid to vapor is possible. This step is difficult, even for pure water. If the product contains two or more components in true solutions or suspensions, the situation can become so complicated that simplified model substances have to be used. Such complex systems occur ubiquitously in biological substances. 

The conditions that apply for the saturated liquid-vapor states can be illustrated with a typical p-v, or (1 /p), diagram for the liquid-vapor phase of a pure substance, as shown in Figure 6.5. The saturated liquid states and vapor states are given by the locus of the f and g curves respectively, with the critical point at the peak. A line of constant temperature T is sketched, and shows that the saturation temperature is a function of pressure only, Tsm (p) or psat(T). In the vapor regime, at near normal atmospheric pressures the perfect gas laws can be used as an acceptable approximation, pv = (R/M)T, where R/M is the specific gas constant for the gas of molecular weight M. Furthermore, for a mixture of perfect gases in equilibrium with the liquid fuel, the following holds for the partial pressure of the fuel vapor in the mixture ... 

Fig. 3.2. A stylized phase diagram for a simple pure substance. The dashed line represents 1 atm pressure and the intersection with the solid-liquid equilibrium line represents the normal boiling point and the intersection with the liquid-vapor equilibrium line represents the normal boiling point.

Draw a phase diagram of water. What is called a phase, component, and degree of freedom How many phases and degrees of freedom are there at different points of the phase diagram of water What is known as the freezing (boiling) point of pure substances ... 

The primary tool for representing the phase behavior of a chemical system is the phase diagram, a graphical roadmap of phase stability domains. For a pure substance, with... 

Surprising behavior of liquid and ice phases is found if we follow various 7, P paths in this extended phase diagram. Sidebar 7.4 illustrates how to determine the expected phase transitions and properties of H20 for various temperatures and pressures far outside the realm of ordinary experience. It is remarkable that such multiplicity of forms and properties can result from a pure substance composed of only a single type of molecule. 

In order to gain a better understanding of the usefulness of phase diagrams, consider a cylinder in which temperature can be controlled and volume varied by injection or removal of mercury as shown in Figure 2-2. Figure 2-2A shows that a pure substance has been trapped in the... 

Fig. 2-4, Typical phase diagram of a pure substance with two lines of isobaric temperature change 123below critical pressure, 45 above critical pressure.

We will first consider phase diagrams. Then we will define the critical point for a two-component mixture. This will be the correct definition for multicomponent mixtures. Also, we will look at an important concept called retrograde condensation. Then the pressure-volume diagram will be discussed, and differences between pure substances and two-component mixtures in the two-phase region will be illustrated. Finally, the effects of temperature and pressure on the compositions of the coexisting liquid and gas will be illustrated. 

Phase Diagram for a Pure Substance — Use of Phase Diagrams — Vapor Pressure of a Pure Substance Pressure-Volume Diagram for a Pure Substance -Density-Temperature Diagram for a Pure Substance Two-Component Mixtures 61... 

Stability Limit 1, With the exception of helium and certain apparent exceptions discussed below. Fig. I gives a universal phase diagram liir all pure compounds The triple point of one P and one T is the single point at which all three phases, crystal, liquid, and gas. are in equilibrium. The triple point pressure is normally below atmospheric. Those substances, c.g.. CO . / - 3H85 mm. 7, = -5ft.fi C. for which it lies above, sublime without melting ai atmospheric pressure. 

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