phase rule

Information about phase rule

Published on October 22, 2010

Author: poonamkulyal



PHASE RULE : PHASE RULE Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. Slide 2: Phase rule is used to study heterogeneous equilibria PHASE It is physically distinct and mechanically separable part of a system which is homogeneous throughout and is separated from other homogeneous part of the system by means of a definite boundary. Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. Slide 3: COMPONENT It is the minimum no. of independent variable constituents by means of which the composition of any phase of the system can be expressed either directly or in the form of a chemical equation. For eg. Water exist in three phases and it forms one component system ice(s)→liquid(l)→vapour(g) Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. Slide 4: DEGREE OF FREEDOM Smallest no. of independent variables such as pressure, Temp and conc. That must be specified in order to describe completely the state of system. It may be uni, bi, tri or non variant. Examples are: for ice- water vapour system, F=0 for saturated Nacl solution, F=1 etc. Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. Slide 5: PHASE RULE This rule is stated in terms of P= no. of phases, C= no. of components and F= degree of freedom for any heterogeneous system. According to this rule- Phase rule: F = C – P + 2 F = no. degrees of freedom C = no. of components P = no. of phases 2 = Temperature and Pressure Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. PHASE DIAGRAM FOR ONE COMPONENT SYSTEM (WATER SYSTEM) : PHASE DIAGRAM FOR ONE COMPONENT SYSTEM (WATER SYSTEM) Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. Slide 7: Description of phase diagram Contains 3 areas AOB,BOC,AOC. phase is one and degree of freedom is 2. Contains 3 curves OA,OB,OC, where phases are 2 but degree of freedom are 1. Contains one triple point O, where all 3 phases coexist and degree of freedom is zero. Curve OA’ is metastable state where water exist as supercooled liquid. Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2. Slide 8: Examples of phase rule : Decomposition of Calcium carbonate Decomposition of ammonium chloride Formation of ammonia Dilute solution of sulphuric acid in water Mixture of NaCl, NaBr,water in equilibrium with vapors Mixture of NaCl, KCl and water Formation of HI Dr.PoonamKulyal_chemistry_AEI_6 & 8.10.09_Lect1,2.

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