Phase transition in the context of Chemical potential

A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combined without reacting, they may form a chemical mixture. If a mixture is separated to isolate one chemical substance to a desired degree, the resulting substance is said to be chemically pure.

Chemical substances can exist in several different physical states or phases (e.g. solids, liquids, gases, or plasma) without changing their chemical composition. Substances transition between these phases of matter in response to changes in temperature or pressure. Some chemical substances can be combined or converted into new substances by means of chemical reactions. Chemicals that do not possess this ability are said to be inert.

Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Virtually all of the ice on Earth is of a hexagonal crystalline structure denoted as ice I_h (spoken as "ice one h"). Depending on temperature and pressure, at least nineteen phases (packing geometries) can exist. The most common phase transition to ice I_h occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. When water is cooled rapidly (quenching), up to three types of amorphous ice can form. Interstellar ice is overwhelmingly low-density amorphous ice (LDA), which likely makes LDA ice the most abundant type in the universe. When cooled slowly, correlated proton tunneling occurs below −253.15 °C (20 K, −423.67 °F) giving rise to macroscopic quantum phenomena.

A complex adaptive system (CAS) is a system that is complex in that it is a dynamic network of interactions, but the behavior of the ensemble may not be predictable according to the behavior of the components. It is adaptive in that the individual and collective behavior mutate and self-organize corresponding to the change-initiating micro-event or collection of events. It is a "complex macroscopic collection" of relatively "similar and partially connected micro-structures" formed in order to adapt to the changing environment and increase their survivability as a macro-structure. The Complex Adaptive Systems approach builds on replicator dynamics.

The study of complex adaptive systems, a subset of nonlinear dynamical systems, is an interdisciplinary matter that attempts to blend insights from the natural and social sciences to develop system-level models and insights that allow for heterogeneous agents, phase transition, and emergent behavior.

Nonmetallic material, or in nontechnical terms a nonmetal, refers to materials which are not metals. Depending upon context it is used in slightly different ways. In everyday life it would be a generic term for those materials such as plastics, wood or ceramics which are not typical metals such as the iron alloys used in bridges. In some areas of chemistry, particularly the periodic table, it is used for just those chemical elements which are not metallic at standard temperature and pressure conditions. It is also sometimes used to describe broad classes of dopant atoms in materials. In general usage in science, it refers to materials which do not have electrons that can readily move around, more technically there are no available states at the Fermi energy, the equilibrium energy of electrons. For historical reasons there is a very different definition of metals in astronomy, with just hydrogen and helium as nonmetals. The term may also be used as a negative of the materials of interest such as in metallurgy or metalworking.

Variations in the environment, particularly temperature and pressure can change a nonmetal into a metal, and vica versa; this is always associated with some major change in the structure, a phase transition. Other external stimuli such as electric fields can also lead to a local nonmetal, for instance in certain semiconductor devices. There are also many physical phenomena which are only found in nonmetals such as piezoelectricity or flexoelectricity.

Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid.

Substances in the molten state generally have reduced viscosity as the temperature increases. An exception to this principle is elemental sulfur, whose viscosity increases in the range of 130 °C to 190 °C due to polymerization.

Fusion welding is a generic term for welding processes that rely on melting to join materials of similar compositions and melting points. Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created in the material (although some techniques, like beam welding, often minimize this effect by introducing comparatively little heat into the workpiece).

In contrast to fusion welding, solid-state welding does not involve the melting of materials.

In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero, i.e. 0 K (−273.15 °C; −459.67 °F). Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which microscopic quantum-mechanical phenomena, particularly wavefunction interference, become apparent macroscopically.More generally, condensation refers to the appearance of macroscopic occupation of one or several states: for example, in BCS theory, a superconductor is a condensate of Cooper pairs. As such, condensation can be associated with phase transition, and the macroscopic occupation of the state is the order parameter.

Bose–Einstein condensates were first predicted, generally, in 1924–1925 by Albert Einstein, crediting a pioneering paper by Satyendra Nath Bose on the new field now known as quantum statistics. In 1995, the Bose–Einstein condensate was created by Eric Cornell and Carl Wieman of the University of Colorado Boulder using rubidium atoms. Later that year, Wolfgang Ketterle of MIT produced a BEC using sodium atoms. In 2001 Cornell, Wieman, and Ketterle shared the Nobel Prize in Physics "for the achievement of Bose–Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates".

In thermodynamics, an irreversible process is a process that cannot be undone. All complex natural processes are irreversible, although a phase transition at the coexistence temperature (e.g. melting of ice cubes in water) is well approximated as reversible.

A change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state by infinitesimal changes in some property of the system without expenditure of energy. A system that undergoes an irreversible process may still be capable of returning to its initial state. Because entropy is a state function, the change in entropy of the system is the same whether the process is reversible or irreversible. However, the impossibility occurs in restoring the environment to its own initial conditions. An irreversible process increases the total entropy of the system and its surroundings. The second law of thermodynamics can be used to determine whether a hypothetical process is reversible or not.

Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which are phase transitions of a substance into a gas), as well as desorption, seepage from cracks or internal volumes, and gaseous products of slow chemical reactions. Boiling is generally thought of as a separate phenomenon from outgassing because it consists of a phase transition of a liquid into a vapor of the same substance.

Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions).In simple words, the change in size of a body due to heating is called thermal expansion. Substances usually contract with decreasing temperature (thermal contraction), with rare exceptions within limited temperature ranges (negative thermal expansion). The SI unit of thermal expansion is inverse Kelvin (1/K).

Temperature is a monotonic function of the average molecular kinetic energy of a substance. In simple words, temperature is the measure of kinetic energy of a body or the measure of hotness or coldness of a body. As energy in particles increases, they start moving faster and faster, weakening the intermolecular forces between them and therefore expanding the substance.When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves.

Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point.

For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid-liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point. It melts at 85 °C (185 °F) and solidifies from 32 to 40 °C (90 to 104 °F).

Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic results. A number of global and regional forecast models are run in different countries worldwide, using current weather observations relayed from radiosondes, weather satellites and other observing systems as inputs.

Mathematical models based on the same physical principles can be used to generate either short-term weather forecasts or longer-term climate predictions; the latter are widely applied for understanding and projecting climate change. The improvements made to regional models have allowed significant improvements in tropical cyclone track and air quality forecasts; however, atmospheric models perform poorly at handling processes that occur in a relatively constricted area, such as wildfires.

Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the weathering and erosion of pieces of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier". As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. The freezing and thawing action of the ice enlarges, widens, or causes further cracks in the bedrock as it changes volume across the ice/water phase transition (a form of hydraulic wedging), gradually loosening the rock between the joints. This produces large chunks of rock called joint blocks. Eventually these joint blocks come loose and become trapped in the glacier.

In this way, plucking has been linked to regelation. Rocks of all sizes can become trapped in the bottom of the glacier. Joint blocks up to three meters have been "plucked" and transported. These entrained rock fragments can also cause abrasion along the subsequent bedrock and walls. Plucking also leads to chatter marks, wedge shaped indentations left on the bedrock or other rock surfaces. Glacial plucking both exploits pre-existing fractures in the bedrock and requires continued fracturing to maintain the cycle of erosion. Glacial plucking is most significant where the rock surface is well jointed or fractured or where it contains exposed bed planes, as this allows meltwater and clasts to penetrate more easily.

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. The verb form of sublimation is sublime, or less preferably, sublimate. Sublimate also refers to the product obtained by sublimation. The point at which sublimation occurs rapidly (for further details, see below) is called critical sublimation point, or simply sublimation point. Notable examples include sublimation of dry ice at room temperature and atmospheric pressure, and that of solid iodine with heating.

The reverse process of sublimation is deposition (also called desublimation), in which a substance passes directly from a gas to a solid phase, without passing through the liquid state.

In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that determines how long an observer has to wait before the new phase or self-organized structure appears. For example, if a volume of water is cooled (at atmospheric pressure) significantly below 0 °C, it will tend to freeze into ice, but volumes of water cooled only a few degrees below 0 °C often stay completely free of ice for long periods (supercooling). At these conditions, nucleation of ice is either slow or does not occur at all. However, at lower temperatures nucleation is fast, and ice crystals appear after little or no delay.

Nucleation is a common mechanism which generates first-order phase transitions, and it is the start of the process of forming a new thermodynamic phase. In contrast, new phases at continuous phase transitions start to form immediately.

In chemistry and thermodynamics, calorimetry (from Latin calor 'heat' and Greek μέτρον (metron) 'measure') is the science or act of measuring changes in state variables of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical reactions, physical changes, or phase transitions under specified constraints. Calorimetry is performed with a calorimeter. Scottish physician and scientist Joseph Black, who was the first to recognize the distinction between heat and temperature, is said to be the founder of the science of calorimetry.

Indirect calorimetry calculates heat that living organisms produce by measuring either their production of carbon dioxide and nitrogen waste (frequently ammonia in aquatic organisms, or urea in terrestrial ones), or from their consumption of oxygen. Lavoisier noted in 1780 that heat production can be predicted from oxygen consumption this way, using multiple regression. The dynamic energy budget theory explains why this procedure is correct. Heat generated by living organisms may also be measured by direct calorimetry, in which the entire organism is placed inside the calorimeter for the measurement.

Frost is a layer of ice on a solid surface, which forms from water vapor that deposits onto a freezing surface. Frost forms when the air contains more water vapor than it can normally hold at a specific temperature. The process is similar to the formation of dew, except it occurs below the freezing point of water typically without crossing through a liquid state.

Air always contains a certain amount of water vapor, depending on temperature. Warmer air can hold more than colder air. When the atmosphere contains more water than it can hold at a specific temperature, its relative humidity rises above 100% becoming supersaturated, and the excess water vapor is forced to deposit onto any nearby surface, forming seed crystals. The temperature at which it will form is called the dew point, and depends on the humidity of air. When the temperature of the air drops below its dew point, excess water vapor is forced out of solution, resulting in a phase change directly from water vapor (a gas) to ice (a solid). As more water molecules are added to the seeds, crystal growth occurs, forming ice crystals. Crystals may vary in size and shape, from an even layer of numerous microscopic-seeds to fewer but much larger crystals, ranging from long dendritic crystals (tree-like) growing across a surface, acicular crystals (needle-like) growing outward from the surface, snowflake-shaped crystals, or even large, knifelike blades of ice covering an object, which depends on many factors such as temperature, air pressure, air motion and turbulence, surface roughness and wettability, and the level of supersaturation. For example, water vapor adsorbs to glass very well, so automobile windows will often frost before the paint, and large hoar-frost crystals can grow very rapidly when the air is very cold, calm, and heavily saturated, such as during an ice fog.