Phase equilibrium Phase diagrams
Phase Equilibrium Phase Diagrams
Definitions F: the number of degrees of freedom, i.e the number of independent variables needed to describe the state of the system C the number of independent substances in the system P: the number of phases in the system where a phase is a form of matter that is uniform throughout in composition and state
Definitions • F: the number of degrees of freedom, i.e. the number of independent variables needed to describe the state of the system. • C: the number of independent substancesin the system. • P: the number of phases in the system, where a phase is a form of matter that is uniform throughout in composition and state
The phase rule Each phase needs C-1 composition variables plus t and p to describe its state Therefore the total number of state variables is P(C-1)+2 For each substance. there are p-1 equi constraints of the form u(a)=u(B) Therefore F=P(C-1)+2-C(P-1) or F=c-p+2
The Phase Rule • Each phase needs C-1 composition variables plus T and p to describe its state. Therefore, the total number of state variables is P(C-1) + 2 • For each substance, there are P-1 equil. constraints of the form () = () • Therefore F = P(C-1) + 2 - C(P-1) or F = C - P + 2
Phase diagram critical point qui I atm solid g as triple point
Phase Diagram solid liquid gas p T critical point triple point 1 atm Tb
Cooling Curve: Pure Substance liquid cooling arrest solid cooling liquid freezing time
Cooling Curve: Pure Substance time T Tf arrest liquid cooling solid cooling liquid freezing