Information about Phase Diagram
physical chemistry, mineralogy, and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. In mathematics and physics, a phase diagram also has an alternative meaning, as a synonym for a phase space.
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. This reflects the fact that, at extremely high temperatures and pressures, the liquid and gaseous phases become indistinguishable, in what is known as a supercritical fluid. In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 22.064 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, the liquid and gaseous phases can blend continuously into each other. However, 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.
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, that is the temperature at which metal melts. However, in the phase diagram for water the solid-liquid phase boundary has a negative slope. This reflects the fact that ice has a lower density than water, which is an unusual property for a material.
One type of phase diagram plots temperature against the relative concentrations of two substances in a binary mixture called a binary phase diagram. Such a mixture can be either a solid solution, eutectic or peritectic, among others. These two types of mixtures result in very different graphs. A textbook example of a eutectic phase diagram is that of the olivine (forsterite and fayalite) system.
Another type of binary phase diagram is a boiling point diagram for a mixture of two components, i. e. chemical compounds. For two particular volatile components at a certain pressure such as atmospheric pressure, a boiling point diagram shows what vapor (gas) compositions are in equilibrium with given liquid compositions depending on temperature. In a typical binary boiling point diagram, temperature is plotted on a vertical axis and mixture composition on a horizontal axis. A simple example diagram with hypothetical components 1 and 2 in a non-azeotropic mixture is shown at right. The fact that there are two separate curved lines joining the boiling points of the pure components means that the vapor composition is usually not the same as the liquid composition the vapor is in equilibrium with. See Vapor-Liquid Equilibrium for a fuller discussion.
In addition to the above mentioned types of phase diagrams, there are thousands of other possible combinations. Some of the major features of phase diagrams include congruent points, where a solid phase transforms directly into a liquid. There is also the peritectoid, a point where two solid phases combine into one solid phase during heating. The inverse of this, when one solid phase transforms into two solid phases during heating, is called the eutectoid.
A complex phase diagram of great technological importance is that of the iron-carbon system for less than 7% carbon (see steel).
The x-axis of such a diagram represents the concentration variable of the mixture. As the mixtures are typically far from dilute and their density as a function of temperature usually unknown the preferred concentration measure is mole fraction. A volume based measure like molarity would be unadvisable.
A triple point is, in a pressure-temperature phase diagram, the unique intersection of the lines of equilibrium between three states of matter, usually solid, liquid, and gas.
For a phase diagram with temperature on the vertical axis, a solidus is a line below which the substance is stable in the solid state. A liquidus is a line above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus; within the gap, the substance is replaced by a mixture of solid crystals and liquid.
Pressure-temperature diagrams
The simplest phase diagrams are pressure-temperature diagrams of a single simple substance, such as water. The axes correspond to the pressure and temperature. The phase diagram shows, in pressure-temperature space, the lines of equilibrium or phase boundaries between the three phases of solid, liquid, and gas.)
A typical phase diagram. The dotted line gives the anomalous behaviour of water. The green lines mark the freezing point and the blue line the boiling point, showing how they vary with pressure.
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. This reflects the fact that, at extremely high temperatures and pressures, the liquid and gaseous phases become indistinguishable, in what is known as a supercritical fluid. In water, the critical point occurs at around 647 K (374 °C or 705 °F) and 22.064 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, the liquid and gaseous phases can blend continuously into each other. However, 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.
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, that is the temperature at which metal melts. However, in the phase diagram for water the solid-liquid phase boundary has a negative slope. This reflects the fact that ice has a lower density than water, which is an unusual property for a material.
Binary phase diagrams
Other much more complex types of phase diagrams can be constructed, particularly when more than one pure component is present. In that case concentration becomes an important variable. Phase diagrams with more than two dimensions can be constructed that show the effect of more than two variables on the phase of a substance. Phase diagrams can use other variables in addition to or in place of temperature and pressure and composition, for example the strength of an applied electrical or magnetic field and they can also involve substances that take on more than just three states of matter.)
A phase diagram for a binary system displaying a eutectic point.
One type of phase diagram plots temperature against the relative concentrations of two substances in a binary mixture called a binary phase diagram. Such a mixture can be either a solid solution, eutectic or peritectic, among others. These two types of mixtures result in very different graphs. A textbook example of a eutectic phase diagram is that of the olivine (forsterite and fayalite) system.
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Boiling Point Diagram
In addition to the above mentioned types of phase diagrams, there are thousands of other possible combinations. Some of the major features of phase diagrams include congruent points, where a solid phase transforms directly into a liquid. There is also the peritectoid, a point where two solid phases combine into one solid phase during heating. The inverse of this, when one solid phase transforms into two solid phases during heating, is called the eutectoid.
A complex phase diagram of great technological importance is that of the iron-carbon system for less than 7% carbon (see steel).
The x-axis of such a diagram represents the concentration variable of the mixture. As the mixtures are typically far from dilute and their density as a function of temperature usually unknown the preferred concentration measure is mole fraction. A volume based measure like molarity would be unadvisable.
Common components of a phase diagram
Lines of equilibrium or phase boundaries refer to the lines that demarcate where phase transitions occur.A triple point is, in a pressure-temperature phase diagram, the unique intersection of the lines of equilibrium between three states of matter, usually solid, liquid, and gas.
For a phase diagram with temperature on the vertical axis, a solidus is a line below which the substance is stable in the solid state. A liquidus is a line above which the substance is stable in a liquid state. There may be a gap between the solidus and liquidus; within the gap, the substance is replaced by a mixture of solid crystals and liquid.
Liquid crystal phase diagrams
In liquid crystal physics, phase diagrams are used in the case of mixing of nematogenic compounds to distinguish between the isotropic liquid phase, the nematic liquid phase.See also
External links
- A collection of about 150 alloy phase diagrams and some PT diagrams
- Iron-Iron Carbide Phase Diagram Example
- How to build a phase diagram
- Phase Changes: Phase Diagrams: Part 1
- Equilibrium Fe-C phase diagram
chemical equilibrium is the state in which the chemical activities or concentrations of the reactants and products have no net change over time. Usually, this state results when the forward chemical process proceeds at the same rate as their reverse reaction.
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An acid dissociation constant, denoted by Ka, is an equilibrium constant for the dissociation of a weak acid. According to the Brønsted-Lowry theory of acids and bases an acid is only recognised by its reaction with a base.
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The binding constant is a special case of the equilibrium constant K. The equilibrium state of molecular binding, i.e. the balance between the binding and dissociation processes after infinite reaction time, may be formalized as the unbound compounds (reactants) transforming into
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chemical equilibrium is the state in which the chemical activities or concentrations of the reactants and products have no net change over time. Usually, this state results when the forward chemical process proceeds at the same rate as their reverse reaction.
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dissociation constant is a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions.
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In the fields of organic and medicinal chemistry, a partition or distribution coefficient (KD) is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium.
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equilibrium constant. See also Determination of equilibrium constants for experimental and computational methods.
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Types of equilibrium constants
Association and dissociation constants
In organic chemistry and biochemistry it is customary to use pKa..... Click the link for more information.
In biochemistry, equilibrium unfolding is the process of unfolding a protein or RNA molecule by gradually changing its solution conditions, i.e., its environment. Since equilibrium is maintained at all steps, the process is reversible (equilibrium folding).
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Separation processes
Processes
Acid-base extraction • Chromatography • Crystallization • Dissolved air flotation • Distillation • Drying • Electrochromatography • Filtration • Flocculation • Froth flotation
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Processes
Acid-base extraction • Chromatography • Crystallization • Dissolved air flotation • Distillation • Drying • Electrochromatography • Filtration • Flocculation • Froth flotation
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The phase rule of Willard Josiah Gibbs in the 1870 is the fundamental rule which phase diagrams are based on.
P + F = C + 2
P is the number of phases present in equilibrium (Types of solid, liquid, gas phases etc).
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P + F = C + 2
P is the number of phases present in equilibrium (Types of solid, liquid, gas phases etc).
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In chemistry, reaction quotient is a quantitative measure of the extent of reaction, the relative proportion of products and reactants present in the reaction mixture at some instant of time.
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Solubility equilibrium is any chemical equilibrium between solid and dissolved states of a compound at saturation.
Solubility equilibria involve application of chemical principles and constants to predict solubility of substances under specific conditions (because
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Solubility equilibria involve application of chemical principles and constants to predict solubility of substances under specific conditions (because
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equilibrium constant. See also Determination of equilibrium constants for experimental and computational methods.
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Types of equilibrium constants
Association and dissociation constants
In organic chemistry and biochemistry it is customary to use pKa..... Click the link for more information.
thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. The local state of a system at thermodynamic equilibrium is determined by the values of its intensive parameters, as pressure, temperature, etc.
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Vapor-liquid equilibrium, abbreviated as VLE by some, is a condition where a liquid and its vapor (gas phase) are in equilibrium with each other, a condition or state where the rate of evaporation (liquid changing to vapor) equals the rate of condensation (vapor changing to
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Physical chemistry is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems<ref name="quanta_physical_chem_1" /> within the field of chemistry traditionally using the principles, practices and
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Mineralogy is an Earth Science focused around the chemistry, crystal structure, and physical (including optical) properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical
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Materials science or materials engineering is an interdisciplinary field involving the properties of matter and its applications to various areas of science and engineering. This science investigates the relationship between the structure of materials and their properties.
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graph of a function f is the collection of all ordered pairs (x,f(x)). In particular, graph means the graphical representation of this collection, in the form of a curve or surface, together with axes, etc.
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thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. The local state of a system at thermodynamic equilibrium is determined by the values of its intensive parameters, as pressure, temperature, etc.
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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).
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Mathematics (colloquially, maths or math) is the body of knowledge centered on such concepts as quantity, structure, space, and change, and also the academic discipline that studies them. Benjamin Peirce called it "the science that draws necessary conclusions".
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Physics is the science of matter[1] and its motion[2][3], as well as space and time[4][5] —the science that deals with concepts such as force, energy, mass, and charge.
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phase space, introduced by Willard Gibbs in 1901, is a space in which all possible states of a system are represented, with each possible state of the system corresponding to one unique point in the phase space.
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Axes is a heteronym; the plural of both axis and axe.
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Axe
- Colloquially, axe is a general name for an electric guitar or a wind instrument in popular music.
- Axe has other meanings not used in the plural.
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Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface.
Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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trillion fold).]]
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. Temperature is one of the principal parameters of thermodynamics.
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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. Temperature is one of the principal parameters of thermodynamics.
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A solid object is in the states of matter characterized by resistance to deformation and changes of volume. At the microscopic scale, a solid has these properties :
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- The atoms or molecules that comprise the solid are packed closely together.
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Liquid is one of the four principal states of matter. A liquid is a fluid that can freely form a distinct surface at the boundaries of its bulk material.
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Characteristics
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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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