Editing Chemistry (section)

===Phase===
[[File:Phase changes.svg|thumb|upright=1.25|Diagram showing relationships among the phases and the terms used to describe phase changes]]
{{Main|Phase (matter)|l1=Phase}}

In addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A ''phase'' is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as [[pressure]] or [[temperature]].

Physical properties, such as [[density]] and [[refractive index]] tend to fall within values characteristic of the phase. The phase of matter is defined by the ''[[phase transition]]'', which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.

Sometimes the distinction between phases can be continuous instead of having a discrete boundary; in this case the matter is considered to be in a [[supercritical fluid|supercritical]] state. When three states meet based on the conditions, it is known as a [[triple point]] and since this is invariant, it is a convenient way to define a set of conditions.

The most familiar examples of phases are [[solid]]s, [[liquid]]s, and [[gas]]es. Many substances exhibit multiple solid phases. For example, there are three phases of solid [[iron]] (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the [[crystal structure]], or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the ''aqueous'' phase, which is the state of substances dissolved in [[aqueous solution]] (that is, in water).

Less familiar phases include [[plasma physics|plasmas]], [[Bose–Einstein condensate]]s and [[fermionic condensate]]s and the [[paramagnetism|paramagnetic]] and [[ferromagnetism|ferromagnetic]] phases of [[magnet]]ic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in [[biology]].