Hemin Hasary MSc. Pharmaceutical sciences Physical Pharmacy Phase equilibria Hemin Hasary MSc. Pharmaceutical sciences

Phases A phase is a homogeneous portion of a system. Uniform chemical and physical properties For example in this glass water and its ice are together. We have two phases with same chemical properties but different physical properties. Same composition (substance, or component), but two phases. In this example if the ice melts, then we will have only one phase.

Phases Here oil and water appear as two phases with different physical and chemical properties. There are again two phase but here two components Here we have two components (alcohol and water) but one phase!

Phases As we mentioned in previous lectures we have three major states of matter. These different states can change to each other. These changes reach a point which is Equilibrium

Equilibrium A system reaches equilibrium if its free energy is at minimum. At equilibrium characteristics of the system do not change with time. i.e it is stable. Changing temperature or pressure will change the system free energy

Equilibrium Is this system at equilibrium? Temp: -1°C pressure: 1 atm

Phase rule Coexistence of phases can only occur over a limited range. phase rule is a relationship for determining the least number of intensive variables that can be changed without changing the equilibrium state of the system. P is the number of phases present C in represents the number of components in the system F is termed the number of degrees of freedom

The number of degrees of freedom: is the least number of intensive variables that must be fixed/known to describe the system completely. Examples of intensive variables are: temperature, pressure, concentration….

Systems Containing One Component

In curve OA the upper limit is critical temp In curve OA the upper limit is critical temp. and lower end is triple point Vapor and liquid coexist in equilibrium Curve OC is sublimation curve, where solid and vapor are in equilibrium OB represent melting curve at which solid and liquid are in equilibrium The negative slope of curve OB shows that the freezing point of water decrease with increasing pressure

If the temp. is held at t1 , the water will in gaseous state above critical temp. regardless to the applied pressure At t2 temp the vapor converts to the liquid state with increasing pressure In the area of t3 temp the vapor changes to ice with increasing pressure and if the applied continuous to be increased the ice will converts to liquid Therefore two conditions must be fixed in order specify the system completely

Systems Containing more than one Component

CONDENSED SYSTEMS a maximum of three degrees of freedom is possible in a two-component system. More components more degrees of freedom In two component one phase system (maximum no of variables) F = 2 – 1 + 2 = 3 E.g. temperature, pressure, and concentration In this case we try to stabilize the pressure so that we deal with only two variables. condensed systems: When we only consider solid and liquid phases Now we can use planar figures instead of three dimensional (this will be easier)

Two-Component Systems Containing Liquid Phases The maximum temperature at which the two-phase region exists is termed the critical solution or (upper consolute temperature). Mixture of cyclohexane and aniline at different conc. exposed to different temp. is example on two- component systems Binodal is obtained from this mixture

Upper and lower consulate temperatures

Two-Component Systems Containing Solid and Liquid Phases: Eutectic Mixtures two components are completely miscible in the liquid state and completely immiscible as solids, There are four regions on the graph, where three of them in two phase and one region has one phase

Eutectic composition “contact melting”: lowest melting temperature over a composition range. eutectic composition is the composition of two or more compounds that exhibits a melting temperature lower than that of any other mixture of the compounds The primary criterion for eutectic formation is the mutual solubility of the components in the liquid or melt phase. Lidocaine and prilocaine, two local anesthetic agents, form a 1:1 mixture having a eutectic temperature of 18◦C

Phase Equilibria in Three-Component Systems In systems containing three components but only one phase. four degrees of freedom are temperature, pressure, and the concentrations of two of the three components. Only two concentration terms are required because the sum of these subtracted from the total will give the concentration of the third component. Temperature and pressure are considered to be constant.

Triangular Diagram

Each corner of triangle represent 100% of one component The three lines joining the corner points represent two components of three possible combinations The area within triangle all possible combinations of A,B and C

Ternary Systems with One Pair of Partially Miscible Liquids e.g. Water and benzene + alchohol Alchohol provide solvation binodal curve

Alterations of the binodal curves with changes in temperature.

Questions !