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An entity of a material system which is uniform in chemical composition and physical state. This tag should be applied to question regarding chemical and physical properties of phases, systems of phases and also phase transition processes.

From the IUPAC goldbook:

phase
An entity of a material system which is uniform in chemical composition and physical state.

phase transition
A change in the nature of a phase or in the number of phases as a result of some variation in externally imposed conditions, such as temperature, pressure, activity of a component or a magnetic, electric or stress field.

Examples for systems of phases:

  • Aqueous solution of sodium chloride (1 phase, liquid)
  • A block of aluminium (1 phase, solid)
  • Air, approximated as a mixture of four parts nitrogen and one part oxygen gas (1 phase, gaseous)
  • Water and diethyl ether (2 phases, liquid)
  • Dry ice in air (2 phases, solid and gaseous)
  • Water and ice (2 phases, solid and liquid)
  • Water, ice and steam in a closed system (idealised at its triple point, 3 phases, solid, liquid and gaseous)

Examples of phase transition:

  • Boiling water (liquid to gaseous)
  • Melting of iron (solid to liquid)
  • sublimation of dry ice (solid to gaseous)

This tag should be applied to question regarding chemical and physical properties of phases, systems of phases and also phase transition processes.

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