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Phase Diagrams

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. These diagrams indicate the physical states that exist under specific conditions of pressure and temperature and also provide the pressure dependence of the phase-transition temperatures (melting points, sublimation points, boiling points). Regions or areas labeled solid, liquid, and gas represent single phases, while lines or curves represent...

Phase Diagram

Phase Diagram

The phase of a given substance depends on the pressure and temperature. Thus, plots of pressure versus temperature showing the phase in each region provide considerable insights into the thermal properties of substances. Such plots are known as phase diagrams. For instance, in the phase diagram for water (Figure 1), the solid curve boundaries between the phases indicate phase transitions (i.e., temperatures and pressures at which the phases coexist).

Phase Diagram

Phase Diagram

A phase diagram is a graphical representation of the physical states of a substance under different conditions of temperature and pressure. It shows the boundaries between solid, liquid, and gas phases and the conditions at which these phases coexist in equilibrium. An area in a phase diagram represents a single phase, whereas lines or phase boundaries represent the equilibrium between two phases.In the phase diagram of water, the boundary line between the solid and liquid states illustrates...

pV-Diagrams

pV-Diagrams

The pV diagram, which is a graph of pressure versus volume of the gas under study, is helpful in describing certain aspects of the substance. When the substance behaves like an ideal gas, the ideal gas equation describes the relationship between its pressure and volume. On a pV diagram, it is common to plot an isotherm, which is a curve showing p as a function of V with the number of molecules and the temperature fixed. Then, for an ideal gas, the product of the pressure of the gas and its...

Le Chatelier's Principle: Changing Volume (Pressure)

Le Chatelier's Principle: Changing Volume (Pressure)

For gas-phase equilibria, changes in the concentrations of reactants and products can occur with altered volume and pressure. The partial pressure, P, of an ideal gas is proportional to its molar concentration, M.

Vapor Pressure

Vapor Pressure

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally collide with the surface of the condensed phase, and in some cases, these collisions will result in the molecules re-entering the condensed phase. The change from the gas phase to the liquid is called condensation. When the rate of condensation becomes equal to the rate of vaporization, neither the amount of the liquid nor the amount of the vapor...

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Related Experiment Video

Updated: Jul 8, 2026

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO₂/Organic/Water Systems

Published on: January 24, 2014

High-pressure phase equilibria with compressed gases.

Wei Ren¹, Aaron M Scurto

¹Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045, USA.

The Review of Scientific Instruments

|January 1, 2008

Summary

This summary is machine-generated.

A new apparatus accurately determines various phase equilibria and critical points under high pressure (up to 300 bars) using minimal sample volumes. This mercury-free device offers reliable data without complex calibration, validated with decane-CO(2) and CO(2)-ionic liquid systems.

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Area of Science:

Thermodynamics
Chemical Engineering
Materials Science

Background:

Accurate determination of phase equilibria is crucial for chemical process design and optimization.
Existing methods for high-pressure equilibrium measurements can be complex, require large sample volumes, or involve hazardous materials like mercury.

Purpose of the Study:

To describe a novel apparatus for precise determination of high-pressure phase equilibria.
To present a mercury-free, low-sample-volume method for measuring vapor-liquid, liquid-liquid, solid-liquid-vapor, and vapor-liquid-liquid equilibria, as well as mixture critical points.

Main Methods:

Development and detailed description of a new high-pressure apparatus.
Operation of the apparatus to determine various equilibrium types and critical points up to 150°C and 300 bars.
Validation of the apparatus using decane-CO(2) and CO(2)-ionic liquid systems, comparing results with literature data.

Main Results:

The apparatus successfully determined multiple phase equilibria and critical points with high accuracy.
Experimental data showed excellent agreement with existing literature values obtained through different methodologies.
A rigorous error analysis confirmed the reliability and precision of the new system.

Conclusions:

The described apparatus provides a versatile and accurate method for high-pressure phase equilibrium determination.
The mercury-free design and low sample volume requirements make it a practical and safe alternative to existing techniques.
The validated performance demonstrates its utility for research and industrial applications in chemical thermodynamics and engineering.