System of two salts and water, Summaries of Kinetics of Phase Transformations

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PHASE RULE

System of two salts and water Presnted by Devikarani D K

Presentation Outline Discussion Points Terms to be known *Phase, *Component, *Degree of freedom, *Phase rule and *Phase diagram. System of two salts and water *Formation of one hydrate and two anhydrous salts

Component:

TWO COMPONENT SYSTEM

A system of saturated solution of NaCl consists of, Solid salt Salt solution Water vapour All these phases can be expressed in terms of Nacl and water,hence it is a two component system. THREE COMPONENT SYSTEM Fe(s)+H2O FeO(S) + H2 (g) This 3 phase can be expressed in 3 component system. The smallest number of independent variable constituents, necessary to describe the composition of each phase.

Number of component of a system. Number of chemical constituents of the system minus the number of equation relating to these constituents in an equilibeium state. DEGREE OF FREEDOM OR VARIANCE (F): A system in equilibrium is affected by the factors such as pressure, temperature and composition of the phases. Varience is defines as the number of independent intensive variables such as temperature, pressure and concentration, which must be fixed in order to define the system completely.

PHASE DIAGRAM A diagram of substance, which illustrated the conditions of equilibrium between various phases of a substance is called as Phase diagram/ Equilibrium diagram. When a system goes one phase to another phase without any change of chemical composition is called as phase transition.

For a three component system, the phase rule becomes F= 5-P. For a system having only one phase, the phase diagram must illustrate four variables, which is difficult. Hence T and P are fixed for a given diagram and traingular graph paper is used to describe the system in terms of te remaining variables - two of three concenrations.

System of two salts and water. A system of two salts and water furnishes an example of three component system involving solids and liquids(fig), shows such a system where the two salts show some solubility and also form saturated solutions. Tie lines are drawn to show the saturated solutions along CD and ED are in equilibrium with solid salts A and B respectively. At point D, the solution is in equilibrium with both the salts A and B, respectively. If water is removed from the system represented by the point D, the total composition moves towards the base triangle. This results in the formation of more solid salts remain in equilibrium with the decreasing amount but constant concentration of the saturated solution. Three component system containing two salts and water at a fixed temperature and pressure.

Triangular plot where both the stable hydrate and the anhydrous salt crystallize together. sometimes under certain conditions of temperature, the stable hydrate as well as the anhydrous salt exist in equilibrium with the solution. In such cases, the triangular plot has an appearance as shown in fig. Formation of one hydrate and two unhydrae solids.

Area AFEGHA: A point in the region represents an unsaturated solution. Area DEFD: A point in this region represents solid hydrate D in equilibrium with the solution, composition of the solution lies on the line EF. Area BFGB: A point in this region represents solid B in equilibrium with the solution, composition of the solution lies on the line FG. Area BDFB: Invarient region where solid hydrate D and solid B are in equilibrium with the solution of composition corresponding to the point F. Area HGCH: A point in this region represents solid C in equilibrium with the solution, composition of the solution lies on the line HG. Area BGCB: Another invarient region, where solid B and solid C are in equilibrium with solution of composition corresponding to the point G.

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