8. Phase Rule.pdf

Phase Equilibria and The Phase Rule Phase Equilibria and The Phase Rule 2  Phase Equilibria and The Phase Rule  Phase rule, which is a relationship for determining the least number of independent variables (e.g., temperature, pressure, density, and co...

Phase Equilibria and The Phase Rule Phase Equilibria and The Phase Rule 2  Phase Equilibria and The Phase Rule  Phase rule, which is a relationship for determining the least number of independent variables (e.g., temperature, pressure, density, and concentration) that can be changed without changing the equilibrium state of the system.  i.e. The number of variables that may be changed independently without causing the appearance of a new phase or disappearance of an existing phase.  i.e. The number of degrees of freedom is the least number of intensive variables that must be fixed/known to describe the system completely. 3 Phase Equilibria and The Phase Rule 4 Phase Equilibria and The Phase Rule 5 Phase Equilibria and The Phase Rule 6 Phase Equilibria and The Phase Rule 7  Phase Equilibria and The Phase Rule  One component systems 8 Phase Equilibria and The Phase Rule 9 Phase Equilibria and The Phase Rule 10 Phase Equilibria and The Phase Rule 11 Phase Equilibria and The Phase Rule Figure 2.Phase diagram for water at moderate pressures. 12 Phase Equilibria and The Phase Rule 13 Phase Equilibria and The Phase Rule 14 Phase Equilibria and The Phase Rule 15 Phase Equilibria and The Phase Rule 16 Phase Equilibria and The Phase Rule 17  Phase Equilibria and The Phase Rule  Two component systems 18 Phase Equilibria and The Phase Rule 19 Phase Equilibria and The Phase Rule 20 Phase Equilibria and The Phase Rule 21 Phase Equilibria and The Phase Rule 22 Phase Equilibria and The Phase Rule  Importance of Tie line: 1. Calculation of the composition of each phase. 2. Determination of the weight of each phases. 23 Phase Equilibria and The Phase Rule 24 Phase Equilibria and The Phase Rule 25 Phase Equilibria and The Phase Rule 26 Phase Equilibria and The Phase Rule 27 Phase Equilibria and The Phase Rule 28 Phase Equilibria and The Phase Rule 29 Phase Equilibria and The Phase Rule 30 Phase Equilibria and The Phase Rule 31 Phase Equilibria and The Phase Rule 32 Phase Equilibria and The Phase Rule 33 Phase Equilibria and The Phase Rule 34  Phase Equilibria and The Phase Rule  Suppose we prepare a system containing 60% by weight of thymol in salol and raise the temperature of the mixture to 50°C. (point X).  On cooling the system remains as a single liquid until the temperature falls to 29°C, at which point a minute amount of solid thymol separates out to form a two-phase solid–liquid system.  As system x is progressively cooled, more and more of the thymol separates as solid. 35  Phase Equilibria and The Phase Rule  As system y is cooled the solid phase that separates at 22°C is pure salol.  The lowest temperature at which a liquid phase can exist in the salol–thymol system is 13°C, and this occurs in a mixture containing 34% thymol in salol.  This point on the phase diagram is known as the eutectic point.  At the eutectic point, three phases (liquid, solid salol, and solid thymol) coexist. 36 Phase Equilibria and The Phase Rule 37  Phase Equilibria and The Phase Rule  Pharmaceutical importance:  Numerous drugs form eutectic mixtures (solid dispersion), with the consequence that they may liquefy at ambient temperature owing to the melting point decrease characteristic at the eutectic point.  Lidocaine and prilocaine, two local anesthetic agents, form a 1:1 mixture having a eutectic temperature of 18°C. 38