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Phase (matter)

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This article is about phases of matter in science. For the general article, see State of matter.

In science, a phase of matter is one of the forms a substance can take, such as solid, liquid or gas. The words "phase" and "state of matter" are often used for the same thing: the three most common phases are solid, liquid and gas, and a fourth, plasma, occurs naturally inside stars.[1] Substances change from one phase to another when conditions such as temperature and pressure change, and these changes can be shown on a phase diagram.[2]

Common phases

Solids, liquids and gases are the phases most commonly found on Earth.[3] A solid is rigid and has a definite shape, while a liquid flows and takes the shape of its container.[4] A gas takes both the shape and the volume of its container.[5] A plasma is like a gas but contains large numbers of electrically charged particles.[6]

Changes of phase

Evaporation, condensation, freezing and melting are all changes of phase, and they are an essential part of the Earth's water cycle.[7]

The temperature at which the solid and liquid phases of a substance can exist together in balance is called the melting point of the solid, or the freezing point of the liquid.[8] At that point, melting and freezing happen at the same rate.[9] A liquid boils when the pressure of its vapour equals the pressure of the gas around it; this temperature is its boiling point.[10]

Some solids can turn straight into a gas without becoming liquid first. This is called sublimation.[11] For example, at room temperature and normal pressure, a piece of dry ice (solid carbon dioxide) slowly seems to disappear without ever forming a liquid.[12]

Phase diagrams

A phase diagram is a chart of pressure against temperature that shows the conditions at which a substance's solid, liquid and gas phases are in balance with each other.[2] It can show special points. Above a certain temperature and pressure, called the critical point, a substance becomes a supercritical fluid, which is a phase of its own.[13] For carbon dioxide, the triple point lies well above normal air pressure, which is why carbon dioxide cannot exist as a liquid under everyday conditions.[14] Some foods are freeze-dried by sublimation at pressures below the triple point of water.[15]

See also

References

  1. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "1.2 Phases and Classification of Matter". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. The three most common states or phases of matter are solid, liquid, and gas. A fourth state of matter, plasma, occurs naturally in the interiors of stars.
  2. ↑ 2.0 2.1 Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.4 Phase Diagrams". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance.
  3. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "1.2 Phases and Classification of Matter". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. Solids, liquids, and gases are the three states of matter commonly found on earth
  4. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "1.2 Phases and Classification of Matter". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. A solid is rigid and possesses a definite shape. A liquid flows and takes the shape of its container
  5. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "1.2 Phases and Classification of Matter". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. A gas takes both the shape and volume of its container.
  6. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "1.2 Phases and Classification of Matter". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. A plasma is a gaseous state of matter that contains appreciable numbers of electrically charged particles
  7. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.3 Phase Transitions". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. consider the evaporation, condensation, freezing, and melting of water. These changes of state are essential aspects of our earth's water cycle
  8. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.3 Phase Transitions". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. The temperature at which the solid and liquid phases of a given substance are in equilibrium is called the melting point of the solid or the freezing point of the liquid.
  9. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.3 Phase Transitions". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. In a mixture of solid and liquid at equilibrium, the reciprocal processes of melting and freezing occur at equal rates
  10. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.3 Phase Transitions". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. The boiling point of a liquid is the temperature at which its equilibrium vapor pressure is equal to the pressure exerted on the liquid by its gaseous surroundings.
  11. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.3 Phase Transitions". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. directly into the gaseous state, bypassing the liquid state, via a process known as sublimation .
  12. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.3 Phase Transitions". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. At room temperature and standard pressure, a piece of dry ice (solid CO 2 ) sublimes, appearing to gradually disappear without ever forming any liquid.
  13. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.4 Phase Diagrams". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. This phase of matter is called a supercritical fluid , and the temperature and pressure above which this phase exists is the critical point
  14. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.4 Phase Diagrams". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. Notice that the triple point is well above 1 atm, indicating that carbon dioxide cannot exist as a liquid under ambient pressure conditions.
  15. ↑ Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019). "10.4 Phase Diagrams". Chemistry 2e. OpenStax, Rice University. Retrieved 18 October 2026. are dehydrated by sublimation at pressures below the triple point for water.
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