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The phase with the highest free energy G at temperature T is the most stable at that T.
False
Entropy S for solid phases is typically large and positive due to high disorder.
False
Gases are most stable at high temperatures due to their low bonding energy and high disorder.
True
The Phase Rule (Gibbs) states that the number of degrees of freedom can be calculated using the formula F=C+P-2.
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At low temperatures, solids tend to be the least stable phase compared to liquids and gases.
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A dosage formulation in pharmaceuticals can contain multiple solid phases and components.
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The intersection of lines representing phases indicates a point where the free energy change ΔG is zero.
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Phase mixtures can vary in temperature and pressure, impacting the number of phases present.
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In a one component system, three phases in equilibrium occur when F is equal to 1.
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A phase diagram can illustrate the stability of phases under varying pressure and temperature conditions.
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At the critical point, a substance cannot exist as either a liquid or a gas.
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In a two component phase diagram, data is typically plotted against varying pressures.
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The triple point of water occurs at a temperature of 0.01 °C and a pressure of 6.1 mbar.
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The formula F = C - P + 2 is used to determine the number of phases in a system.
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Carbon dioxide has a triple point at a pressure of 73.8 bar.
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Phases in equilibrium can only be solid and liquid, but not vapor.
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The critical temperature for carbon dioxide is 31.1 °C.
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The variable F represents the number of phases in equilibrium in a system.
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In a ternary phase diagram, the point representing 60% surfactant, 40% solubilizate, and 0% water refers to point B.
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The point representing pure oil, pure water, and pure alcohol will each be located at the corners of the triangular phase diagram.
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Point D in the phase diagram composition estimates a higher percentage of water than that of oil.
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At the upper critical point p in a two-phase system, the composition is represented by a single phase.
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In the given system at 25 °C, a composition of 60% oil, 30% water, and 10% alcohol results in one liquid phase.
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The eutectic point occurs at a temperature where both solid and liquid phases coexist.
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At the eutectic point of the C6H6 and C10H8 mixture, the composition is 50% C6H6 and 50% C10H8.
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The melting point of paracetamol is higher than that of citric acid.
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Cooling a solution of 50% C6H6 and 50% C10H8 to 10 °C will result in no solid formation.
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Solidus temperature is the point where all components are solid.
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In liquid mixtures, A-A and B-B interactions dominate over A-B interactions.
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The phase diagram for a binary mixture can help estimate the composition at the eutectic point.
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Mixtures of paracetamol and citric acid show consistent solidus temperatures across various mole fractions.
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The lever rule can be used to determine the ratio of masses of solid and liquid phases in a mixture.
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The liquidus temperature for a mole fraction of 0.6 paracetamol is 137 °C.
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Two liquid phases with stronger A-A and B-B interactions than A-B exist above the upper critical temperature.
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At the lower critical temperature, A-B interactions are stronger than A-A and B-B interactions.
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Triangular phase diagrams can represent systems with three components at constant temperature and pressure.
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Hexane and aniline are examples of A and B being fully miscible in a liquid phase.
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A-B interactions are always weak in systems where two separate liquid phases exist.
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Complex formation between A and B can lead to a situation where two liquid phases exist at the lower critical temperature.
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At point o in a ternary phase diagram, the composition is always equal to 1:1:1 for three components.
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In a two-liquid phase system, when the temperature decreases, both phases tend to dissolve into each other.
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Paraldehyde and saline represent a specific example of two components that exhibit complex formation.
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A mixture of alcohol, oil, and water systems will always result in only a single liquid phase.
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Study Notes
Phases in Pharmaceuticals
- A dosage formulation (medicine) typically contains multiple phases and components.
- Understanding the factors that determine the extent and stability of the differing phases is crucial.
- Pharmaceutical formulations can involve gas, multiple liquid, and multiple solid phases.
Phase Equilibria
- The phase with the lowest free energy (G) at a given temperature (T) is the most stable at that temperature.
- Free energy is represented by the equation: G = H - TS, where H is enthalpy, T is temperature, and S is entropy.
- For solid phases, enthalpy (H) is large and negative due to bonding between molecules, while entropy (S) is small due to low disorder.
- Solids tend to be the most stable phase at low temperatures.
- For gas phases, enthalpy (H) is close to 0, as there is no bonding between molecules, while entropy (S) is large and positive due to high disorder.
- Gases are most stable at high temperatures.
- Liquid phases exist in between solid and gas phases.
G as a Function of Temperature for a Pure Substance
- The temperature at which a solid melts is called the melting/fusion temperature (Tfus).
- The temperature at which a liquid vaporizes is called the vaporization temperature (Tvap).
- For a pure substance, the free energy of the solid and liquid phase are equal at the melting/fusion temperature (Tfus).
- Similarly, the free energy of the liquid and gas phase are equal at the vaporization temperature (Tvap).
Mixtures of Phases and Components
- The Phase Rule (Gibbs) determines the number of degrees of freedom (F) possible for a system at equilibrium.
- The Phase Rule equation is: F = C - P + 2, where C is the number of components, P is the number of phases, and the "+2" accounts for variation in temperature and pressure.
- One component, three phases in equilibrium: F = 0 (triple point).
- One component, two phases in equilibrium: F = 1.
- Phase Diagrams illustrate which phases are stable under specific conditions.
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).
- The point where three phases are in equilibrium is known as the triple point.
- The critical point is the point above which a substance exists as a supercritical fluid, combining aspects of liquid and gas phases.
Two Component Phase Diagram
- Shows which phase (solid, liquid, or vapor) is the most stable at a given pressure (P) and temperature (T).
- The eutectic point is the point at which liquid and both solids are in equilibrium.
- The liquidus line represents the point where the system is entirely liquid.
- The solidus line represents the point where the system is entirely solid.
Mixtures of Liquids (A and B)
- In mixtures, A-B interactions can occur in addition to A-A and B-B interactions in pure liquids.
- The strength of A-B interactions relative to A-A/B-B interactions determines the number of phases and is temperature-dependent.
Two Liquids: Upper Critical Temperature
- At temperatures above the upper critical temperature, A and B are fully miscible (one liquid phase).
- At temperatures below the upper critical temperature, A and B are partially miscible (two liquid phases).
- Examples: hexane/aniline, hexane/nitrobenzene
Two Liquids: Lower Critical Temperature
- At temperatures below the lower critical temperature, A and B are fully miscible (one liquid phase).
- At temperatures above the lower critical temperature, A and B are partially miscible (two liquid phases).
- Can occur when A-B interactions involve complex formation.
- Examples: triethylamine/water, paraldehyde/saline
Three Component Systems
- Can be represented 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.
Alcohol (or Surfactant), Oil, and Water Systems
- Alcohol is fully miscible with both water and oil.
- Oil and water are partially miscible, forming two separate liquid phases.
- The boundary between one liquid phase and two liquid phases can be determined empirically.
- The point where the two liquid phases become one is called the upper critical point.
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Description
This quiz covers the concepts of phases in pharmaceuticals, focusing on dosage formulation and the importance of phase stability. It explores the relationship between free energy, enthalpy, and entropy in determining the stability of different phases such as solid, liquid, and gas. Understand the critical factors influencing pharmaceutical formulations.
