Eutectic Systems in Chemistry

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Questions and Answers

The reduced phase rule is given by the formula F = C − P + ______

In the phase diagram, the 'x axis' shows composition in terms of [%A and %B] and the 'y axis' represents ______.

temperature (T)

The eutectic point is the specific point at which liquid and ______ are in equilibrium.

both solids

A simple eutectic system has regions of all liquid at higher ______ and all solid at lower temperature.

temperature Signup and view all the answers

In a simple eutectic system, one region contains solid A at higher ______% and the other contains solid B at higher %B.

A Signup and view all the answers

The components A and B in the example of a simple eutectic system are naphthalene (C10H8) and ______ (C6H6).

benzene Signup and view all the answers

The phase diagram described has four regions: all liquid, all solid, and ______ regions of solid suspended in solution.

two Signup and view all the answers

The eutectic point can only be measured ______ and is characteristic of the system.

empirically Signup and view all the answers

Pharmaceuticals can exist in multiple ______ and components.

phases Signup and view all the answers

The phase with the lowest free energy G at temperature T is the most ______ at that T.

stable Signup and view all the answers

For solid phases, enthalpy H is large and ______.

negative Signup and view all the answers

Gas phases have enthalpy H close to ______.

0 Signup and view all the answers

The Phase Rule states that F = C - P + ______.

2 Signup and view all the answers

At low temperatures T, solids tend to be the most ______ phase.

stable Signup and view all the answers

For gas phases, the entropy S is large and ______.

positive Signup and view all the answers

Phase equilibria can be understood through the relationship G = H − ______S.

TS Signup and view all the answers

The temperature of melting or fusion is denoted as ______.

Tfus Signup and view all the answers

At equilibrium, the free energies of both phases are equal, resulting in ______ G = 0.

ΔG Signup and view all the answers

In a one component phase diagram, when F = 0, it indicates the ______ point.

triple Signup and view all the answers

When there are two phases in equilibrium, F equals ______.

1 Signup and view all the answers

The general phase diagram for a pure substance shows the most stable phase at given pressure ______ and temperature T.

P Signup and view all the answers

Above the critical ______, a substance exists as a supercritical fluid.

point Signup and view all the answers

For carbon dioxide, the critical point is at a temperature of ______ °C.

31.1 Signup and view all the answers

At the triple point of water, the temperature is ______ °C.

0.01 Signup and view all the answers

In a two component phase diagram, composition is plotted against constant ______.

pressure Signup and view all the answers

In a phase diagram, a supercritical fluid combines aspects of both liquid and ______ phases.

gas Signup and view all the answers

The A-B interactions are dependent on ______.

temperature Signup and view all the answers

The equation F = C − P + 2 relates to the number of ______ in a system.

components Signup and view all the answers

The stable phases shown in a phase diagram include solid, liquid, and ______.

vapor Signup and view all the answers

At the upper critical temperature, the system can exhibit ______ liquid phases.

two Signup and view all the answers

______ can occur when A-B involves complex formation.

Lower critical temperature Signup and view all the answers

In three-component systems, triangular phase diagrams represent the compositions of ______ components.

three Signup and view all the answers

At point o in a triangular phase diagram, the composition is represented as ______.

1:2:3 Signup and view all the answers

In a two liquid phase system at lower critical temperature, A-A and B-B interactions are ______ than A-B.

stronger Signup and view all the answers

Hexane and aniline are examples of liquids that can exhibit ______ miscibility.

full Signup and view all the answers

The apices of a triangular phase diagram represent ______ components.

pure Signup and view all the answers

The systems involving alcohol, oil, and water typically require a ______ to stabilize the mixture.

surfactant Signup and view all the answers

At lower critical temperatures, the system may exhibit ______ solutions.

saturated Signup and view all the answers

The composition of point A is 50% solubilizate, 30% ______, and 20% surfactant.

water Signup and view all the answers

At point B, the composition is 60% surfactant, 40% solubilizate, and ______% water.

0 Signup and view all the answers

In the ternary phase diagram, pure oil, pure water, and pure ______ are the three corner points.

alcohol Signup and view all the answers

A system can exist in two liquid phases when the compositions are ______ and 60% water.

30% oil Signup and view all the answers

The upper critical point in the phase diagram is labeled as point ______.

p Signup and view all the answers

Study Notes

Temperature

A system with two components (A and B) can have four regions: all liquid, all solid, two regions of solid suspended in solution (one with solid A, the other with solid B), and a single point (the eutectic point) where liquid and both solids are in equilibrium.
The eutectic point is the point where liquid and both solids are in equilibrium, at a fixed temperature and composition.
The reduced phase rule (F = C − P + 1) is used to determine the number of degrees of freedom in a system.

Simple Eutectic System

A simple eutectic system is characterized by a phase diagram with four regions: all liquid, all solid, two regions of solid suspended in solution, and a single eutectic point.
The eutectic point is a characteristic of the system and can only be determined empirically.
An example of a simple eutectic system is a mixture of naphthalene (C10H8) and benzene (C6H6).

Phases in Pharmaceuticals

Phases are homogenous portions of physical material bounded by interfaces.
A dosage formulation (medicine) will typically contain multiple phases and components.
Pharmaceutically, there can be gas, multiple liquid, and multiple solid phases.

Phase Equilibria

The phase with the lowest free energy (G) at a given temperature is the most stable at that temperature.
For solid phases, enthalpy (H) is large and negative due to bonding between molecules, and entropy (S) is small due to low disorder. This means that solids are more stable at lower temperatures.
For gas phases, enthalpy (H) is close to zero due to no bonding between molecules, and entropy (S) is large and positive due to high disorder. This means that gases are more stable at higher temperatures.
Liquid phases are in between solid and gas phases.

G as a Function of T for a Pure Substance

The free energy (G) of a pure substance is a function of temperature (T).
The temperature of melting/fusion (Tfus) and the temperature of vaporization (Tvap) are points where the lines of the free energy of the different phases intersect.
At the intersection points, the free energy of both phases is equal (ΔG = 0).

Mixtures of Phases and Components

If a system has C components and P phases at equilibrium, each component can be present in each phase.
Temperature (T) and pressure (P) can be varied.
The Phase Rule (Gibbs) determines the number of degrees of freedom (F) that exist for changing parameters without producing or losing phases.

The Phase Rule

The Phase Rule is expressed as F = C − P + 2.
The "+ 2" accounts for variation in temperature and pressure.
F represents the number of degrees of freedom, C represents the number of components, and P represents the number of phases.
A system with one component and three phases in equilibrium (triple point) has zero degrees of freedom (F = 0).
A system with one component and two phases in equilibrium has one degree of freedom (F = 1).
Phase diagrams can be used to illustrate which phases are stable under specific conditions.

General Phase Diagram for a Pure Substance

A general phase diagram for a pure substance shows which phase (solid, liquid, or vapor) is the most stable at a given pressure (P) and temperature (T).
Triple points represent the points where three phases are in equilibrium.
Critical points represent the points above which the substance exists as a supercritical fluid.

Two Component Phase Diagram

Two-component phase diagrams are dependent on temperature and are plotted with composition vs. A-B interactions at constant pressure.

Two Liquids; Upper Critical Temperature

The upper critical temperature is the temperature above which two liquids are fully miscible in all proportions (one liquid phase).
Below the upper critical temperature, the two liquids are partially miscible (two liquid phases).
Examples of systems that exhibit an upper critical temperature include hexane/aniline and hexane/nitrobenzene.

Two Liquids; Lower Critical Temperature

The lower critical temperature is the temperature below which two liquids are fully miscible in all proportions (one liquid phase).
Above the lower critical temperature, the two liquids are partially miscible (two liquid phases).
Systems that exhibit a lower critical temperature often involve complex formation.
Examples of systems that exhibit a lower critical temperature include triethylamine/water and paraldehyde/saline.

Three Component Systems

Three-component systems can be illustrated using triangular (ternary) phase diagrams at constant temperature and pressure.
The apices of the triangle represent the pure components.
Points on the sides represent mixtures of two components.
The composition of a point within the triangle can be determined by drawing lines from each apex to the point.
The ratio of the lengths of the lines represents the ratio of the components in the mixture.

Alcohol (or Surfactant), Oil and Water Systems

Alcohol (or surfactants) are fully miscible with water and oil in all proportions.
Oil and water are partially miscible, meaning they only form one liquid phase at certain compositions.
Ternary phase diagrams can be used to illustrate the phase behavior of these systems.
Tie lines connect the compositions of the two liquid phases in equilibrium.
Upper critical points represent the temperature above which the system becomes fully miscible.

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Explore the fascinating world of eutectic systems through this quiz. You will learn about the different phases, the eutectic point, and the reduced phase rule. Test your knowledge on simple eutectic systems and their applications in pharmaceuticals.