what is Gribb's Phare rule ? Define and explain Various terms invovled in Phase rules with suitable examples
Answers
Answer:
The phase rule describes the possible number of degrees of freedom in an enclosed system at equilibrium, in terms of the number of separate phases and the number of chemical constituents in the system. It was deduced by J.W Gibbs in the 1870s.
Explanation:
Definition of Phase Rule:
Provided he equilibrium between any no.of phases is not influence by gravitational force electrical force, magnetic forces or by surface actions & it is influenced only by temperature, pressure, concentration then the no.of degrees of freedom (F) of the system is related to the no.of components (C) & of phases (P) the phase rule equation-
F=C−P+2
Phase−−−−−: Any homogeneous & physically district & mechanically separable portion of a system by definite boundary surfaces.
Eg;-
At freezing point water contains three phases. Ice(s)→ water(I)→water vapor(g)
Mixture of gases → consists of one phase.
Two completely miscible liquids → consist of one phase
A solution of a substance in solvent → consists of one phase
A heterogeneous mixture-
CacO3→CaO+CO2→ consist of three phases.
2.Component−−−−−−−−−−: The smallest number of independent variable Constituents which are required to express the composition of each phase in the system.
Eg:-
In water system Ice(s)→water(I)→(g)
The composition of all three phases are same i.e. H2O.
Therefore it is one component system.
Decomposition of CaCO3→CaO(s)+CO2→two Compoenent system
Solution of any salt → one component system.
Fe(s)+H2O(g)→FeO(s)+H2(g)→threecomponent system.
Degree of freedom−−−−−−−−−−−−−−−−→Minimum no.of independently variable factors such as temperature pressure & concentration of the phase which must be arbitrarily specified in order to represent perfectly the condition of a system
Eg.
In water system Ice(s)→ Water (I)→Vapor (g)
Here P=3 & C=1
Therefore F=C−P+2=1−3+2=0
Therefore this is variant system, or non variant system or
Invariant system. If condition eg. Temperature or pressure is altered, the three phases will not be in equilibrium & one of the phases would disappear.
Water(I)→Vapor (g)Here C=1 & P=2
Therefore this is univariant system. Hence either temperature or pressure has to be specified to define the system completely.
Water vapors Here P=1, C=1 Therefore this is bivariant system.Hence both temperature and Pressure has to be specified to define the system completely.
A mixture of gases like N2 & H2 Here C=2 & P=1
Therefore this is trivariant system. Hence temperature, pressure as well as volume have to be specified