Phase diagram equilibrium states

The science dealing with phase transitions is thermodynamics. Using thermodynamics, we may discuss which phase will eventually be formed when a material (of composition c and phase p) is maintained under the same conditions for an infinite time, and the phase reaches the minimum energy state (equilibrium state) under given thermodynamic conditions (temperature and pressure). Experimentally, a phase diagram (equilibrium phase diagram) is prepared, and we may use the data... 

The equilibrium state of a system can be represented by a point in a (c + 2)-dimensional diagram. Phase diagrams are state diagrams for open systems, in which a particular state of equilibrium is specihed by the values of c + 2 independent state variables (the rest ate hxed dependent variables), with additional information on the phases present under various conditions. Although one typically sees phase diagrams with potentials (T) P, /a) chosen as the state variables, there are actually many possible ways to select the set of independent variables. 

A one-component system (C = 1) has two independent state variabies (T and p). At the tripie point three phases (soiid, iiquid, vapour) coexist at equiiibrium, so P = 3. From the phase ruie f = 0, so that at the tripie point, T and p are fixed - neither is free but both are uniqueiy determined. If T is free but p depends on T (a sloping line on the phase diagram) then f = 1 and P = 2 that is, two phases, solid and liquid, say, co-exist at equilibrium. If both p and T are free (an area on the phase diagram) F = 2 and P = 1 only one phase exists at equilibrium (see Fig. A1.18). 

The shaded region is that part of the phase diagram where liquid and vapor phases coexist in equilibrium, somewhat in analogy to the boiling line for a pure fluid. The ordinary liquid state exists on the high-pressure, low-temperature side of the two-phase region, and the ordinary gas state exists on the other side at low pressure and high temperature. As with our earlier example, we can transform any Type I mixture... 

Fig. 8.8 The principle of the Dyson model. Each point in the phase diagram represents a possible composition of a molecular population. The horizontal axis is a, where (a+ 1) is the number of monomer types. On the vertical axis, b represents the quality factor of the polymeric catalysis. The transition region consists of populations which can have both an ordered and a disordered equilibrium state. In the death region there are only disordered states, while in the immortal region (in the Garden of Eden ), there is no disordered state (Dyson, 1988)...

An equilibrium exists between a liquid and its vapor. This is just one of several equilibria that exist between the states of matter. A phase diagram is a graph representing the relationship of all the states of matter of a substance. One type of phase diagram relates the states to temperature and pressure. This type allows us to predict which state of matter will exist at a certain temperature and pressure combination. Figure 11-1 shows a general form of a phase diagram. 

The triple point is the combination of temperature and pressure on a phase diagram where all three states of matter exist in equilibrium. 

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