Features of a Phase Diagram

Some of the critical features of a phase diagram include:

• Fusion Curve: Shows the transition between liquid and solid phases.
• Vaporization Curve: Represents the transition between gaseous and liquid phases.
• Sublimation Curve: Illustrates the transition between gaseous and solid phases.

Solid-liquid Equilibrium

Solid-liquid equilibrium is a critical aspect of phase diagrams, as it represents the boundary between a substance’s solid and liquid phases. The solid-liquid equilibrium phase diagram shows the temperature and pressure conditions under which a substance exists in a solid or liquid state and the conditions where both phases coexist in equilibrium.

The key features of a solid-liquid equilibrium phase diagram include:

• Melting Point: The temperature at which a solid substance melts and becomes a liquid.
• Freezing Point: The temperature at which a liquid substance freezes and becomes a solid.
• Fusion Curve: The line on the phase diagram separates the solid and liquid phases.
• Triple Point: The point where all three phases (solid, liquid, gas) coexist in equilibrium.
• Critical Point: The endpoint of a phase boundary beyond which no distinction exists between two phases due to loss of surface tension.

Liquid-Vapor Diagram

Liquid-Vapor equilibrium (VLE) refers to the distribution of a chemical species between the vapor and liquid phases, particularly at equilibrium. The vapor-liquid equilibrium phase diagram describes the relationship between temperature, pressure, and the compositions of the vapor and liquid phases.

Critical aspects of liquid-vapor equilibrium include:

• Vapor Pressure: The concentration of vapor in contact with its liquid, especially at equilibrium, is often expressed in terms of vapor pressure, which is a partial pressure (part of the total gas pressure).
• Boiling Point: The temperature at which a liquid begins to boil and form a vapor, assuming constant pressure.
• Dalton’s Law: When the sum of the individual component partial pressures equals the overall pressure, Dalton’s law applies.
• Raoult’s Law: Describes the relationship between a solution’s vapor pressure and its pure components’ vapor pressure.
• Lever Rule: Used to calculate the amount of each component in the vapor and liquid phases when two phases are present.

Vapor-liquid equilibrium diagrams help determine the number of equilibrium stages in separation processes like distillation.

Phase diagram is the representation of temperature, pressure, and the distinct phases of a substance (i.e. solid, liquid, and gas) within a closed system. It illustrates the equilibrium between solid, liquid, gas, and sometimes supercritical fluid phases, with lines indicating boundaries where two phases coexist. Key points on a phase diagram include the triple point, critical point, fusion curve (melting), vaporization curve, and sublimation curve, each representing specific phase transitions.

In this article, we will look into what a phase diagram is, its definitions, components, types, applications, etc., in detail.