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What is the temperature at which a minute amount of solid thymol separates out to form a two-phase solid-liquid system in system X?
What is the temperature at which a minute amount of solid thymol separates out to form a two-phase solid-liquid system in system X?
What is the composition of the mixture at the eutectic point in the salol-thymol system?
What is the composition of the mixture at the eutectic point in the salol-thymol system?
What is the consequence of forming eutectic mixtures in pharmaceuticals?
What is the consequence of forming eutectic mixtures in pharmaceuticals?
What is the eutectic temperature of the 1:1 mixture of lidocaine and prilocaine?
What is the eutectic temperature of the 1:1 mixture of lidocaine and prilocaine?
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What happens as system X is progressively cooled?
What happens as system X is progressively cooled?
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What is the lowest temperature at which a liquid phase can exist in the salol-thymol system?
What is the lowest temperature at which a liquid phase can exist in the salol-thymol system?
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What is the primary purpose of the phase rule in thermodynamics?
What is the primary purpose of the phase rule in thermodynamics?
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What does the number of degrees of freedom represent in the context of phase equilibria?
What does the number of degrees of freedom represent in the context of phase equilibria?
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What is the primary characteristic of a one-component system in terms of phase equilibria?
What is the primary characteristic of a one-component system in terms of phase equilibria?
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What is the purpose of a phase diagram, such as the one shown in Figure 2?
What is the purpose of a phase diagram, such as the one shown in Figure 2?
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What is the significance of the phase rule in understanding the behavior of a system at equilibrium?
What is the significance of the phase rule in understanding the behavior of a system at equilibrium?
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What is the primary purpose of a tie line in a two-component system?
What is the primary purpose of a tie line in a two-component system?
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What is the relationship between the number of degrees of freedom and the number of intensive variables in a system?
What is the relationship between the number of degrees of freedom and the number of intensive variables in a system?
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What is the minimum number of phases present in a two-component system at equilibrium?
What is the minimum number of phases present in a two-component system at equilibrium?
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What happens to the composition of the phases when the temperature of a two-component system is increased?
What happens to the composition of the phases when the temperature of a two-component system is increased?
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What is the purpose of the phase rule in a two-component system?
What is the purpose of the phase rule in a two-component system?
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Suppose we prepare a system containing 60% by weight of thymol in salol and raise the temperature of the mixture to 50°C. What can be said about the system at this point?
Suppose we prepare a system containing 60% by weight of thymol in salol and raise the temperature of the mixture to 50°C. What can be said about the system at this point?
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What is the importance of knowing the composition of each phase in a two-component system?
What is the importance of knowing the composition of each phase in a two-component system?
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What is the role of the tie line in determining the weight of each phase?
What is the role of the tie line in determining the weight of each phase?
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What happens to the weight of each phase when the temperature of a two-component system is increased?
What happens to the weight of each phase when the temperature of a two-component system is increased?
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Study Notes
Phase Equilibria and The Phase Rule
- The phase rule is a relationship that determines the least number of independent variables (e.g., temperature, pressure, density, and concentration) that can be changed without changing the equilibrium state of the system.
- The number of variables that may be changed independently without causing the appearance of a new phase or disappearance of an existing phase is referred to as 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.
One Component Systems
- A phase diagram for water at moderate pressures is shown in Figure 2.
Two Component Systems
- Importance of Tie line:
- Calculation of the composition of each phase.
- Determination of the weight of each phase.
Phase Diagrams and Eutectic Points
- A system containing 60% by weight of thymol in salol:
- Remains a single liquid until the temperature falls to 29°C, at which point a minute amount of solid thymol separates out to form a two-phase solid–liquid system.
- As the system is progressively cooled, more and more of the thymol separates as solid.
- A system containing salol and thymol:
- The solid phase that separates at 22°C is pure salol.
- The lowest temperature at which a liquid phase can exist in the salol–thymol system is 13°C, and this occurs in a mixture containing 34% thymol in salol.
- This point on the phase diagram is known as the eutectic point, where three phases (liquid, solid salol, and solid thymol) coexist.
Pharmaceutical Importance
- Numerous drugs form eutectic mixtures (solid dispersion), with the consequence that they may liquefy at ambient temperature owing to the melting point decrease characteristic at the eutectic point.
- Example: Lidocaine and prilocaine, two local anesthetic agents, form a 1:1 mixture having a eutectic temperature of 18°C.
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Description
Understand the phase rule, which determines the minimum independent variables required to maintain equilibrium in a system, and how it relates to degrees of freedom.
