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Encyclopedia > Melting point

The melting point of a solid is the temperature range at which it changes state from solid to liquid. Although the phrase would suggest a specific temperature and is commonly and incorrectly used as such in most textbooks and literature, most crystalline compounds actually melt over a range of a few degrees or less. At the melting point the solid and liquid phase exist in equilibrium. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point. Because of the ability of some substances to supercool, the freezing point is not considered to be a characteristic property of a substance. 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. ... For other uses, see Liquid (disambiguation). ... Amy Poehler portraying a recovering supercool user who is also an alcoholic moments before she disrobes in a public park. ...

## Fundamentals GA_googleFillSlot("encyclopedia_square");

Melting points (in blue) and boiling points (in pink) of the first eight carboxylic acids (°C)

For most substances, melting and freezing points are essentially equal. For example, the melting point and freezing point of the element mercury is 234.32 kelvin (−38.83 °C or −37.89 °F). However, certain substances possess differing solid-liquid transition temperatures. For example, agar melts at 85 °C (185 °F) and solidifies from 31 °C to 40 °C (89.6 °F to 104 °F); this process is known as hysteresis. Image File history File links Size of this preview: 800 Ã— 499 pixelsFull resolution (921 Ã— 574 pixel, file size: 46 KB, MIME type: image/jpeg) Melting points (in blue) and boiling points (in pink) of the first eight Carboxylic acids (temperatures in Â°C,) File historyClick on a date/time to view... Image File history File links Size of this preview: 800 Ã— 499 pixelsFull resolution (921 Ã— 574 pixel, file size: 46 KB, MIME type: image/jpeg) Melting points (in blue) and boiling points (in pink) of the first eight Carboxylic acids (temperatures in Â°C,) File historyClick on a date/time to view... In chemistry, carboxylic acids (also called alkanoic acids) are organic acids characterized by the presence of a carboxyl group. ... In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ... In physics and chemistry, freezing is the process whereby a liquid turns to a solid when cold enough. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... This article is about the element. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... This does not adequately cite its references or sources. ... A system with hysteresis can be summarised as a system that may be in any number of states, independent of the inputs to the system. ...

Certain materials, such as glass, may harden without crystallizing; these are called amorphous solids. Amorphous materials as well as some polymers do not have a true melting point as there is no abrupt phase change at any specific temperature. Instead, there is a gradual change in their viscoelastic properties over a range of temperatures. Such materials are characterized by a glass transition temperature which may be roughly defined as the "knee" point of the material's density vs. temperature graph. This article is about the material. ... Wax and paraffin are amorphous. ... Viscoelasticity, also known as anelasticity, describes materials that exhibit both viscous and elastic characteristics when undergoing plastic deformation. ... The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). ...

The melting point of water at 1 atmosphere of pressure is very close [1] to 0 °C (32 °F, 273.15 K), this is also known as the ice point. In the presence of nucleating substances the freezing point of water is the same as the melting point, but in the absence of nucleators water can supercool to −42 °C (−43.6 °F, 231 K) before freezing. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Supercool redirects here. ...

Unlike the boiling point, the melting point is relatively insensitive to pressure because the solid/liquid transition represents only a small change in volume.[2][3] Melting points are often used to characterize organic compounds and to ascertain the purity. The melting point of a pure substance is always higher and has a smaller range than the melting point of an impure substance. The more impurity is present, the lower the melting point and the broader the range. Eventually, a minimum melting point will be reached. The mixing ratio that results in the lowest possible melting point is known as the eutectic point. Italic text This article is about the boiling point of liquids. ... This article is about pressure in the physical sciences. ... ... A eutectic or eutectic mixture is a mixture of two or more phases at a composition that has the lowest melting point, and where the phases simultaneously crystallise from molten solution at this temperature. ...

The chemical element with the highest melting point is tungsten, at 3695 K (3422 °C, 6192 °F) making it excellent for use as filaments in light bulbs. The often-cited carbon does not melt at ambient pressure but sublimates at about 4000 K; a liquid phase only exists above pressures of 10 MPa and estimated 4300–4700 K. Tantalum hafnium carbide (Ta4HfC5) is a refractory compound with a very high melting point of 4488 K (4215 °C, 7619 °F).[4] At the other end of the scale, helium does not freeze at all at normal pressure, even at temperatures infinitesimally close to absolute zero; pressures over 20 times normal atmospheric pressure are necessary. The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... For other uses, see Tungsten (disambiguation). ... For other uses, see Carbon (disambiguation). ... Sublimation of an element or substance is a conversion between the solid and the gas phases with no intermediate liquid stage. ... For other uses, see Pascal. ... Tantalum hafnium carbide (Ta4HfC5) is a refractory compound with an extremely high melting point of 4488 K (4215 Â°C, 7619 Â°F). ... The term refractory can refer to multiple things: A refractory clergyman is one who refused to swear an oath to the French Revolution-era French state under the Civil Constitution of the Clergy. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... For other uses, see Absolute Zero (disambiguation). ...

## Melting point measurements

Many Laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient (range room temperature to 300°C). Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point. Differential scanning calorimetry gives information on melting point together with its Enthalpy of fusion. Wikipedia does not yet have an article with this exact name. ... Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature. ... Standard enthalpy change of fusion of period three. ...

A basic melting point apparatus for the analysis of crystalline solids consists of a oil bath with a transparent window (most basic design: a Thiele tube) and a simple magnifier. The several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated (and stirred) and with the aid of the magnifier (and external light source) melting of the individual crystals at a certain temperature can be observed. In contemporary devices this optical detection is automated. An oil bath is a laboratory heating device which uses boiling oil as the temperature regulator. ... The Thiele tube, named after the German chemist Johannes Thiele, is a laboratory glassware designed to contain and heat an oil bath. ...

## Thermodynamics

Pressure dependence of water melting point (MPa/K)

Not only is heat required to raise the temperature of the solid to the melting point, but the melting itself requires heat called the heat of fusion. Image File history File links Melting_curve_of_water. ... Image File history File links Melting_curve_of_water. ... Heat of fusion is the amount of heat energy which must be absorbed or lost for 1 gram of a substance to change states from a solid to a liquid or vice versa. ...

From a thermodynamics point of view, at the melting point the change in Gibbs free energy (ΔG) of the material is zero, because the enthalpy (H) and the entropy (S) of the material are increasing (ΔHS > 0). Melting phenomenon happens when the Gibbs free energy of the liquid becomes lower than the solid for that material. At various pressures this happens at a specific temperature. It can also be shown that: In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or Î”H, or rarely as Ï‡) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ... For other uses, see: information entropy (in information theory) and entropy (disambiguation). ...

$Delta S = frac {Delta H} {T}$

The "T","ΔS", and "ΔH" in the above are respectively the temperature at the melting point, change of entropy of melting, and the change of enthalpy of melting. For other uses, see Temperature (disambiguation). ... For other uses, see: information entropy (in information theory) and entropy (disambiguation). ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or Î”H, or rarely as Ï‡) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...

## Carnelley’s Rule

In organic chemistry Carnelley’s Rule established in 1882 by Thomas Carnelley, states that high molecular symmetry is associated with high melting point [5]. Carnelley based his rule on examination of 15,000 chemical compounds. For example for three structural isomers with molecular formula C5H12 the melting point increases in the series isopentane −160 °C (113 K) n-pentane −129.8 °C (143 K) and neopentane −18 °C (255 K). Likewise in xylenes and also dichlorobenzenes the melting point increases in the order meta, ortho and then para. Pyridine has a lower symmetry than benzene hence its lower melting point but the melting point again increases with diazine and triazines. Many cage-like compounds like adamantane and cubane with high symmetry have very high melting points. Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, the halogens as... Molecular symmetry in chemistry describes symmetry in molecules and the classification of molecules in groups based on symmetry. ... In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of bonds between atoms, but in which the atoms are arranged differently. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Pentane also known as amyl hydride or skellysolve is an alkane hydrocarbon with the chemical formula CH3(CH2)3CH3. ... Pentane also known as amyl hydride or skellysolve is an alkane hydrocarbon with the chemical formula CH3(CH2)3CH3. ... Pentane also known as amyl hydride or skellysolve is an alkane hydrocarbon with the chemical formula CH3(CH2)3CH3. ... The term xylenes refers to a group of 3 benzene derivatives which encompasses ortho-, meta-, and para- isomers of dimethyl benzene. ... 시발 놈 ... Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon. ... Pyridine is a chemical compound with the formula C5H5N. It is a liquid with a distinctively putrid odour. ... For benzine, see petroleum ether. ... Diazine refers to a group of organic compounds having the molecular formula C4H4N2. ... A triazine is one of three organic chemicals, isomeric with each other, whose empirical formula is C3H3N3. ... Adamantane (tricyclo[3. ...

A high melting point results from a high heat of fusion or a low entropy of fusion or a combination. In highly symmetrical molecules the crystal phase is densely packed with many efficient intermolecular interactions resulting in a higher enthalpy change on melting. Heat of fusion is the amount of heat energy which must be absorbed or lost for 1 gram of a substance to change states from a solid to a liquid or vice versa. ... The Entropy of fusion of a substance represents the increase in the degree of disorder involved in the transition from an organized crystalline solid to the disorganized structure of a liquid. ...

## See also

Italic text This article is about the boiling point of liquids. ... Freezing-point depression is the difference between the freezing points of a pure solvent and a solution mixed with a solute. ... This is a list of the chemical elements, sorted by melting point measured at normal pressure. ... In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ... // Melting point Notes All values at standard pressure (101. ... 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. ... In physics, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium. ... This article needs to be wikified. ...

## References

1. ^ The melting point of purified water has been measured to be 0.002519 +/- 0.000002 degrees Celsius - see R. Feistel and W. Wagner (2006). "A New Equation of State for H2O Ice Ih". J. Phys. Chem. Ref. Data 35: 1021-1047.
2. ^ The exact relationship is expressed in the Clausius-Clapeyron relation.
3. ^ J10 Heat: Change of aggregate state of substances through change of heat content: Change of aggregate state of substances and the equation of Clapeyron-Clausius. Retrieved on 2008-02-19.
4. ^ hafnium entry at Britannica.com
5. ^ Melting Point and Molecular Symmetry R. J. C. Brown, R. F. C. Brown Journal of Chemical Education 724 Vol. 77 No. 6 June 2000

The Clausius-Clapeyron relation, in thermodynamics, is a way of characterizing the phase transition between two states of matter, such as solid and liquid. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... [[Media:Italic text]]{| style=float:right; |- | |- | |} is the 50th day of the year in the Gregorian calendar. ... Journal of Chemical Education (JCE) is a monthly, subscription-only journal available in print and online. ...

Results from FactBites:

 Periodic Table : Periodic properties : Melting point: Definition (279 words) The melting point is the temperature at which the vapour pressure of the solid and the liquid are the same and the presssure totals one atmosphere. Thus, the melting point of water is = 0°C = 273.15 K and the boiling point of water is = 100°C = 373.15 K On the Fahrenheit scale (°F), the melting point of water = 32°F while the boiling point = 212°F. Therefore the degree size is different on the Fahrenheit scale with 180 Fahrenheit degrees = 100 centigrade degrees.
 The MSDS HyperGlossary: Freezing Point (335 words) The normal freezing point is the temperature at a substance melts (or freezes) at one atmosphere (760 torr = 760 mm Hg = 14.7 psi = 101.3 kPa) of pressure. Melting points can be determined by visual inspection or by monitoring the temperature of the liquid with time. Melting points may be lowered (depressed) by the addition of a soluble material to the solution.
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