Phase Theory
- Phase = part of system which is chemically and physically uniform throughout
- Drug must be in a molecular state
- to show biological activity
- Helps explain how to convert a solid phase drug substance –> molecular state
Number of Phases in a System
Gas
Only 1 Phase exists
Gases are completely miscible
Number of Phases in a System
Liquid
Multiple phases may exist
not all liquids are miscibile with each other
Ex. water + oil + mercury
Number of Phases in a System
Solid
Multiple phases MAY exist
most solids are immiscibile w/ other solids
Vapor pressure of a Liquid
Kinetic Energy is NOT distributed evenly at the interface
Some molecules have more energy –> higher velocity
High energy molecules –> break away from surface of liquid
–> pass into gaseous state
Equilibrium Vapor Pressure
- Dynamic equilibrium between
- Vaporization & Condensation
- saturated vapor exists above the liquid
- Dependent on:
- Temperature –> kinetic energy
- Pressure –> distance between molecules
Critical Temperature
Temperature above @ which a
Liquid can no longer exist
irrespective of pressure
- Above Crit temperature = Supercritical fluid
- formed that has both liquid/gas -like properties
Critical Pressure
Pressure required to:
Liquefy a gas @ its critical temperature
= highest vapor pressure a liquid can have
Phase Rule
F = C - P + 2
F = C - P + 2
- F = # of degrees of freedom
- C = # of components
- P = # of phases
Phase
The homogenous portion of the system
that is seperated from orther portions of the system
by bounding surfaces
- Ex. Water + Water Vapor
- 2 phases : liquid + gas
F = # Degrees of Freedom
- LEAST # of intensive variables
- needed to be FIXED to define the system completely
- INCREASING # of components
- –> Increasing F
- INCREASING # of phases
- –> Decreasing F
One Component Systems
Triple Point
Temperature @ which gas/liquid/solid phases
are at EQUILIBRIUM
F = 0
zero degrees of freedom
1 component - 3 phases + 2 = 0
Vapor Pressure Curve
One Component Systems
Liquid + Water in EQ
positive slope
Above critical temperature –> supercritical fluid
=not a liquid nor a gas
Melting Point
One Component Systems
AKA Freezing Point Curve
Solid + Liquid @ EQ
NEGATIVE SLOPE
freezing point decreases as pressure INCREASES
Sublimation Curve
One Component Systems
Solid + Gas @ EQ
no liquid phase present
Crystillization
Reqires TIME
Needs to OVERCOME an energy barrier (nucleation)
to supercool liquid water without forming ice
Condensed System
When only concerned w/
Liquid & Solid Phases
in a system where we
DISREGARD VAPOR PHASE
fixed @ 1atm pressure
Two Component Liquid-Liquid System
Phenol + Water
Within curve = 2 phases in Equilibrium
Outside curve = 1 liquid phases
Critical Solution Temperature
= Consulate Temperature
Two Component Liquid-Liquid System
Maximum temperature
@ which still 2 liquid phases exist
top of the curve
Tie Line
Two Component Liquid-Liquid System
Region Containing 2 phases
Nicotine-Water System
Two Component Liquid-Liquid System
Shows Upper & Lower Consulate Temperatures
Two Component Liquid-SOLID System
Components
1) Completely miscible in Liquid State
2) Completely Miscible in Solid State
Four Regions
Two Component Liquid-SOLID System
- Single Liquid Phase
- Solid Salol + Conj Liquid Phase
- Solid Thymol + Conj liquid
- BOTH SOLID
- @ lowest temperatures
Eutectic Point
Two Component Liquid-SOLID System
Lowest Temp @ which 2 solids are
@ equilibrium with the LIQUID PHASE
