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Chemistry Stack Exchange

Questions tagged [phase]

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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Molten vs Liquid

When I start studying electrochemistry, I learn the words “molten” and “aqueous”. I don't have a problem for “aqueous”, but I'm a little bit confused about “molten”. For me, “molten” means melt, which means to become liquid from solid. But why do we…
Simon-Nail-It
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Which elements tend to form the most phases?

Some combinations of two elements have very complicated binary phase diagrams across the weight% horizontal axis. Others are rather simple. Is this a function of only one or both of the elements involved? I would think both. However, surely there…
Dale
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Open Database of Phase Diagrams?

Is there some kind of database that has information about phase diagrams of different substances? I'm mostly looking for phase diagrams of elements (silicon, iron, hydrogen, etc.) because I'm trying to write a planetary generator, but I cannot find…
feralin
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At what temperature CO2 becomes solid at normal pressure?

I have met contradicting evidence. The phase diagrams show that $\ce{CO2}$ solidifies at $-78.5\ ^{\circ} \mathrm{C}$: Wikipedia confirms this At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures…
Anixx
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Does any compound exist with multiple liquid phases?

I've seen some phase diagrams and I found really interesting, how many exotic solid phases of most elements exist on higher pressure and temperature. But I've seen always only a single liquid phase and also only a single gaseous phase. The second is…
peterh
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Why can't Carbon Dioxide be liquid at 1 atm?

Wikipedia says that Carbon Dioxide cannot be liquid under atmospheric pressure. I thought the phase of an element was related to both pressure and temperature. If that is so, then should you not be able to set the temperature conditions such…
Vaccano
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How are phase transition diagrams calculated?

How are diagrams such as above plotted? Since empirical studies are slightly off from the 'ideal', what is the source for the phase plots?
Layman
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What are some examples of pure substances with no liquid state?

For example, A molecular substance that decomposes before melting, and under pressure can only assume a liquid state that doesn't contain the same molecules, for example a mixture of the elements of which it's composed A polymer that breaks down…
Brian
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Phase diagram analysis

The figure is a portion of the titanium copper phase diagram for which only single-phase regions are labeled. Specify all temperature composition points at which eutectics, eutectoids, peritectics and congruent phase transformations occur. I think…
user3778
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Are there attempts to investigate phase states at negative pressure?

Phase diagrams of various compounds and systems usually include only positive pressure. But I wonder whether it is possible to somehow investigate them under negative pressure? Are there materials that change phase if mechanically stretched? For…
Anixx
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Why Does an Area in Phase Diagram Considered as Having Degree Of Freedom=1?

Why did the area in the center are Considered as Having 1 Degree Of Freedom. Aren't we able to change the concentration and the temperature at the sametime without changing the Phase? Here is the link to the document…
Vieri_Wijaya
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Why don't substances have a condensation point?

All substances have a freezing point at which they transition from a liquid to a solid. They all also have a melting point at which they transition from a solid to a liquid. However, as far as I can tell a substance only has a boiling point at which…
jlftfeisall
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Bonding and Phase Changes?

When water boils into water vapor, its temperature (average kinetic energy) does not change because the inputed energy is used to break its bonds. But how does that work? Also, in a liquid, aren’t intermolecular bonds broken and reformed constantly…
lightweaver
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Is it possible to have non metallic lithium

I have heard that hydrogen under extremely high pressure and cold temperatures can enter a metallic phase (or just ungodly amounts of pressure and high temperature) Can the inverse of this be applied to lithium? Under very low pressures (and low…
Sidharth Ghoshal
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What is the phase of matter that has flexible volume, but constant shape?

In this YouTube video it argued that: Solids have constant volume, and constant shape Liquids have constant volume, but flexible shape Gases have flexible volume, and flexible shape (in fact they don't have volume and shape at all) So, this table…
Saeed Neamati
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