Phase Flashcards
A stable phase structure with lowest free-energy (internal energy) of a system
Phase equilibrium
Defined as any homogeneous and physically distinct part of a system that is separated from other parts of the system by definite boundaries.
Phase
Solid + solid= 2 phase
Liquid + miscible liquid= 1 phase
Mixtureof gases–onephase
System of water and vapour – 2 phase system
System of water, vapour and ice at equilibrium – 3 phase system
the smallest number of independently varying chemical constituents which the composition of each and every phase in the system can be expressed.
Component
Eg.
The system of ice, water, and vapour – component is 1, since each phase is expressed as H2O.
Mixture of salt and water – 2 component because two independent chemical entities.
the minimum number of variables such as: temperature, pressure or concentration which must be fixed in order to define the system completely.
Degree of freedom/variance
What is the degree of variance of a gaseous mixture of CO2 and N2.
Three variables: pressure, temperature and composition are required to define this system. This is, hence, a trivariant system.
What is the degree of freedom water ice
univariant system., either temperature or pressure
If the pressure on the system is maintained at 1 atm, then the temperature of the system gets automatically fixed at 0oC, the normal melting point of ice. •
What is the phase rule
F = C-P+2
F, the number of degrees of freedom of the system
C= number of components, P= number of phases
The relationship determining the least number variables, that can be changed without altering the equilibrium state of the system.
Phase rule
Who postulated phase rule
J. Willard Gibbs
