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In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i.e. density, crystal structure, index of refraction, and so forth.) The most familiar examples of phases are solids, liquids, and gases. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates, strange matter, liquid crystals, superfluids and supersolids and the paramagneticParamagnetism is the tendency of the atomic magnetic dipoles, due to quantum-mechanical spin, in a material that is otherwise non-magnetic to align with an external magnetic field. This alignment of the atomic dipoles with the magnetic field tends to stre and ferromagneticFerromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. It is responsible for most of the magnetic behavior encountered in everyday life, and is the basis for all permanen phases of magnetThis article is about magnetized material. Magnet is also the name of a commune in the Allier departement, in France A magnet is an object that has a magnetic field. A so-called permanent magnet is made of a ferromagnetic material. Such materials consistic materials.Phases are sometimes called states of matter, but this term can lead to confusion with thermodynamicThermodynamics is the physics of energy, heat, work, entropy and the spontaneity of processes. Thermodynamics is closely related to statistical mechanics from which many thermodynamic relationships can be derived. While dealing with processes in which sys states. For example, two gases maintained at different pressures are in different thermodynamic states, but the same "state of matter".
1 Definitions
Although phases are conceptually simple, they are hard to define precisely. A good definition of a phase of a system is a region in the parameter space of the system's thermodynamic variables in which the free energyIn thermodynamics, free energy is a measure of the amount of work that can be extracted from a system. In this sense, it measures not the energy content of the system, but the "useful energy" content. In different situations, free energy is related to int is analyticIn mathematics, an analytic function is one that is locally given by a convergent power series. Complex analysis teaches us that if a function f of one complex variable is differentiable in some open disk D centered at a point c in the complex field, then. Equivalently, two states of a system are in the same phase if they can be transformed into each other without abrupt changes in any of their thermodynamic properties.
All the thermodynamic properties of a system -- the entropyFor other uses of the term entropy see Entropy (disambiguation The thermodynamic entropy ''S often simply called the entropy in the context of chemistry and thermodynamics, is a measure of the amount of energy in a physical system which cannot be used to, heat capacityHeat capacity (abbreviated C or just C also called thermal capacity is the ability of matter to store heat. The heat capacity of a certain amount of matter is the quantity of heat (measured in Joules) required to raise its temperature by one kelvin. The S, magnetization , compressibility, and so forth -- may be expressed in terms of the free energy and its derivatives. For example, the entropy is simply the first derivative of the free energy with temperature. As long as the free energy remains analytic, all the thermodynamic properties will be well-behaved.
When a system goes from one phase to another, there will generally be a stage where the free energy is non-analytic. This is known as a phase transition. Familiar examples of phase transitions are melting (solid to liquid), freezing (liquid to solid), boiling (liquid to gas), and condensation (gas to liquid). Due to this non-analyticity, the free energies on either side of the transition are two different functions, so one or more thermodynamic properties will behave very differently after the transition. The property most commonly examined in this context is the heat capacity. During a transition, the heat capacity may become infinite, jump abruptly to a different value, or exhibit a "kink" or discontinuity in its derivative.
Possible graphs of heat capacity (C) against temperature (T) at a phase transition.
In practice, each type of phase is distinguished by a handful of relevant thermodynamic properties. For example, the distinguishing feature of a solid is its rigidity; unlike a liquid or a gas, a solid does not easily change its shape. Liquids are distinct from gases because they have much lower compressibility: a gas in a large container fills the container, whereas a liquid forms a puddle in the bottom. Not all the properties of solids, liquids, and gases are distinct; for example, it is not useful to compare their magnetic properties. On the other hand, the ferromagnetic phase of a magnetic material is distinguished from the paramagnetic phase by the presence of bulk magnetization without an applied magnetic field.
Metastable states may sometimes be considered as phases, although strictly speaking they aren't because they are unstable.
