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. Physical science is an encompassing term for the branches of Natural science and Science that study non-living systems in contrast to the biological sciences e. density, crystal structure, index of refraction, and so forth). The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium

Phases vs. states of matter

Phases are sometimes confused with states of matter, but there are significant differences. A state of matter (or physical state, or form of matter) has physical properties which are qualitatively different from other states of matter States of matter refers to the differences between gases, liquids, solids, plasma, etc. This page is about the physical properties of gas as a state of matter Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound If there are two regions in a chemical system that are in different states of matter, then they must be different phases. A state of matter (or physical state, or form of matter) has physical properties which are qualitatively different from other states of matter However, the reverse is not true -- a system can have multiple phases which are in equilibrium with each other and also in the same state of matter. This difference is especially important when considering the Gibbs' phase rule, which governs the number of allowed phases. Gibbs' phase rule, stated by Josiah Willard Gibbs in the 1870s is the fundamental rule on which Phase diagrams are based

Mixtures can have multiple phases, which often happen when two immiscible substances dissolve into one another in small amounts. Miscibility is a term commonly used in Chemistry that refers to the property of Liquids to mix in all proportions forming a Homogeneous Solution For example, a mixture might be composed of an oil phase (95% oil, 5% water) and a water phase (95% water, 5% oil).

Polymorphism is the ability of a sold to exist in more than one crystal form. Polymorphism in Materials science is the ability of a solid material to exist in more than one form or Crystal structure For example, water ice is ordinarily found in the hexagonal form Ice Ih, but can also exist as the cubic ice Ic, the rhombohedral ice II, and many other forms. Ice is a Solid phase, usually crystalline, of a Non-metalic substance that is liquid or gas at Room temperature, such as Ammonia Ice Ih is the hexagonal crystal form of ordinary Ice, or frozen water. Ice Ic is a metastable cubic Crystalline variant of Ice. The Oxygen atoms are arranged in a diamond structure In Crystallography, the rhombohedral (or trigonal) Crystal system is one of the seven lattice point groups named after the two-dimensional Ice II is a Rhombohedral crystalline form of Ice with highly ordered structure

Amorphous phases are also possible with the same molecule, such as amorphous ice. An amorphous solid is a Solid in which there is no Long-range order of the positions of the Atoms (Solids in which there is long-range atomic order are Amorphous ice is an Amorphous solid form of water meaning it consists of Water molecules that are randomly arranged like the atoms of common Glass. In this case, the phenomenon is known as polyamorphism. In Materials science polyamorphism is the ability of a substance to exist in several different Amorphous modifications

For pure chemical elements, polymorphism is known as allotropy. Allotropy (Gr allos, other and tropos, manner is a behavior exhibited by certain Chemical elements these elements can exist in two or more different For example, diamond, graphite, and fullerenes are different allotropes of carbon. In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. "C60" and "C-60" redirect here For other uses see C60 (disambiguation. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6

General definition of phases

In general, two different states of a system are in different phases if there is an abrupt change in their physical properties while transforming from one state to the other. Conversely, two states are in the same phase if they can be transformed into one another without any abrupt changes. There are, however, exceptions to this statement -- for example the liquid-gas critical point discussed below in the Phase Diagrams section.

An important point is that different types of phases are associated with different physical qualities. When discussing the solid, liquid, and gaseous phases, we talked about rigidity and compressibility, and the effects of varying the pressure and volume, because those are the relevant properties that distinguish a solid, a liquid, and a gas. On the other hand, when discussing paramagnetism and ferromagnetism, we look at the magnetization, because that is what distinguishes the ferromagnetic phase from the paramagnetic phase. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it Several more examples of phases will be given in the following section.

In more technical language, a phase is a region in the parameter space of thermodynamic variables in which the free energy is analytic; between such regions there are abrupt changes in the properties of the system, which correspond to discontinuities in the derivatives of the free energy function. In Generative art people talk about parameter space as the set of possibleparameters for a generative system In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering This article is about both real and complex analytic functions As long as the free energy is analytic, all thermodynamic properties (such as entropy, heat capacity, magnetization, and compressibility) will be well-behaved, because they can be expressed in terms of the free energy and its derivatives. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity Magnetization is defined as the quantity of Magnetic moment per unit volume In Thermodynamics and Fluid mechanics, compressibility is a measure of the relative volume change of a Fluid or Solid as a response Mathematicians (and those in related sciences very frequently speak of whether a mathematical object &mdash a Number, a function, a set, a space In Calculus, a branch of mathematics the derivative is a measurement of how a function changes when the values of its inputs change For example, the entropy is the negative of the first derivative of the free energy with temperature (at constant pressure). In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature

When a system goes from one phase to another, there will generally be a stage where the free energy is non-analytic. This is a phase transition. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another 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. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity During a transition, the heat capacity may become infinite, jump abruptly to a different value, or exhibit a "kink" or discontinuity in its derivative. In Calculus, a branch of mathematics the derivative is a measurement of how a function changes when the values of its inputs change See also differential scanning calorimetry. Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of Heat required to increase the Temperature

Possible graphs of heat capacity (C) against temperature (T) at a phase transition

Phase diagrams

Main article: Phase diagram

The different phases of a system may be represented using a phase diagram. In Physical chemistry, Mineralogy, and Materials science, a phase diagram is a type of graph used to show the equilibrium conditions The axes of the diagrams are the relevant thermodynamic variables. For simple mechanical systems, we generally use the pressure and temperature. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature

A phase diagram for a typical material exhibiting solid, liquid and gaseous phases

The markings on the phase diagram show the points where the free energy is non-analytic. The open spaces, where the free energy is analytic, correspond to the phases. The phases are separated by lines of non-analyticity, where phase transitions occur, which are called phase boundaries.

In the diagram, the phase boundary between liquid and gas does not continue indefinitely. Instead, it terminates at a point on the phase diagram called the critical point. In Physical chemistry, Thermodynamics, Chemistry and Condensed matter physics, a critical point, also called a critical state At temperatures and pressure above the critical point, the physical property differences that differentiate the liquid phase from the gas phase become less defined. This reflects the fact that, at extremely high temperatures and pressures, the liquid and gaseous phases become indistinguishable. In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 22. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic 064 MPa.

The existence of the liquid-gas critical point reveals a slight ambiguity in our above definitions. When going from the liquid to the gaseous phase, one usually crosses the phase boundary, but it is possible to choose a path that never crosses the boundary by going to the right of the critical point. Thus, phases can sometimes blend continuously into each other. This new phase which has some properties that are similar to a liquid and some properties that are similar to a gas is called a supercritical fluid. A supercritical fluid is any substance at a Temperature and Pressure above its Thermodynamic critical point. We should note, however, that this does not always happen. For example, it is impossible for the solid-liquid phase boundary to end in a critical point in the same way as the liquid-gas boundary, because the solid and liquid phases have different symmetry. Symmetry in physics refers to features of a Physical system that exhibit the property of Symmetry —that is under certain transformations, aspects of these

An interesting thing to note is that the solid-liquid phase boundary in the phase diagram of most substances, such as the one shown above, has a positive slope. This is due to the solid phase having a higher density than the liquid, so that increasing the pressure increases the melting temperature. However, in the phase diagram for water the solid-liquid phase boundary has a negative slope. Water is a common Chemical substance that is essential for the survival of all known forms of Life. This reflects the fact that ice has a lower density than water, which is an unusual property for a material.

Phase separation

Phase separation is transformation of a homogenous system into two (or more) phases and commonly encountered in many branches of science and technology. One example is the crystallization of a solid from a solution. Crystallization is the (natural or artificial process of formation of solid Crystals precipitating from a homogeneous --> identical Solution A universal mathematical model of phase separation is provided by the Cahn–Hilliard equation. The Cahn–Hilliard equation is an Equation of Mathematical physics which describes the process of phase separation by which the two components of a binary

Phase equilibrium

The distribution of kinetic energy among molecules is not uniform, and it changes randomly. This means that at, say, the surface of a liquid, there may be an individual molecule with enough kinetic energy to jump into the gas phase. Likewise, individual gas molecules may have low enough kinetic energy to join other molecules in the liquid phase. This phenomenon means that at any given temperature and pressure, multiple phases may co-exist.

For example, under standard conditions for temperature and pressure, a bowl of liquid water in dry air will evaporate until the partial pressure of gaseous water equals the vapor pressure of water. In Physical sciences standard conditions for temperature and pressure are Standard sets of conditions for experimental measurements to allow comparisons to be made In a mixture of Ideal gases each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium At this point, the rate of molecules leaving and entering the liquid phase becomes the same (due to the increased number of gaseous water molecules available to re-condense). The fact that liquid molecules with above-average kinetic energy have been removed from the bowl results in evaporative cooling. Evaporative coolers (also called swamp, desert, or air coolers) are devices that cool air through the simple Evaporation of water Similar processes may occur on other types of phase boundaries.

Gibbs' phase rule relates the number of possible phases, variables such as temperature and pressure, and whether or not an equilibrium will be reached. Josiah Willard Gibbs ( February 11, 1839 &ndash April 28, 1903) was an American theoretical Physicist, Chemist Gibbs' phase rule, stated by Josiah Willard Gibbs in the 1870s is the fundamental rule on which Phase diagrams are based

Phase transition

A phase transition or, phase change, describes when a substance changes its state of matter - ex. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another ice melting to water is a phase change because a solid changed to a liquid. For a phase change to occur, energy must be added or removed from the substance. The heat energy, or enthalpy, associated with a solid to liquid transition is the enthalpy of fusion, that for liquid to gas is the enthalpy of vaporization, and for solid to gas is the heat of sublimation. The standard Enthalpy of fusion (symbol \Delta{}H_{fus} also known as the heat of fusion or specific melting heat, is the amount of The enthalpy of vaporization, (symbol \Delta{}_{v}H also known as the heat of vaporization or heat of evaporation, is the Energy required The heat of sublimation, or Enthalpy of sublimation, is defined as the Heat required to sublime one mole of the substance at a given Normally adding or removing energy will change the temperature of the substance as the kinetic energy of the particles will increase or decrease. During a phase change however, the potential energy of the substance changes as the particles are moved further apart or closer together. There is no change in kinetic energy of the particles and therefore no resulting change in temperature.

External links

• French physicists find a solution that reversibly solidifies with a rise in temperature - α-cyclodextrin, water, and 4-methylpyridine

See also

• Condensed matter physics
• Cooling curve
• Supercooling
• Superheating
• Multiphasic liquid