melting point


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melting point,

temperaturetemperature,
measure of the relative warmth or coolness of an object. Temperature is measured by means of a thermometer or other instrument having a scale calibrated in units called degrees. The size of a degree depends on the particular temperature scale being used.
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 at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific temperature; thus melting point is a characteristic of a substance and can be used to identify it. When heat is applied continuously and in sufficient quantity to such solids, the temperature rises steadily until it reaches the point at which liquefaction occurs. Here the rise ceases and no further change in temperature is observed until all of the substance has been converted to liquid. The heat being applied to the substance at that temperature is consumed in bringing about the change of state, and none is available to raise the temperature of that part of the substance already liquefied until all of it has changed to the liquid. If heat is still applied when liquefaction is complete, the temperature will begin to rise again. The quantity of heat necessary to change one gram of any substance from solid to liquid at its melting point is known as its latent heatlatent heat,
heat change associated with a change of state or phase (see states of matter). Latent heat, also called heat of transformation, is the heat given up or absorbed by a unit mass of a substance as it changes from a solid to a liquid, from a liquid to a gas, or the
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 of fusion and differs for different substances. Ice, for example, requires approximately 80 calories of heat to change each gram to water at its melting point. Because its heat of fusion is relatively high, ice is used in refrigeration. In freezing (the reverse process, i.e., the change from liquid to solid), heat is given off by the substance undergoing the change, and the amount given off is the same as that absorbed in melting.

Melting Point

 

(mp), the temperature of the equilibrium phase transition of a crystalline (solid) body to liquid at a constant external pressure. The melting point is a particular case of the temperature of the first-order phase transition. The melting points of several substances at standard pressure (760 mm Hg, or 101,325 newtons per m2) are shown in Table 1.

Table 1
Substancemp (°C)
Hydrogen ...............–259.14
Oxygen ...............–218.4
Nitrogen ...............– 209.86
Argon ...............–189.2
Ethyl alcohol ...............–112.0
Methyl alcohol ...............–97.8
Acetone ...............–94.6
Mercury ...............–38.9
Ethylone glycol ...............–15.6
Nitrobenzene ...............5.7
Acetic acid ...............16.7
Glycerine ...............17.9
Cesium ...............28.5
Naphthalene ...............80.2
Sodium ...............97.8
Iodine ...............112.9
D-Camphor ...............178.5
Aluminum ...............660.37
Copper ...............1083.4
Iron ...............1539.0
Tungsten ...............3410.0

melting point

[′melt·iŋ ‚pȯint]
(thermodynamics)
The temperature at which a solid of a pure substance changes to a liquid. Abbreviated mp.
For a solution of two or more components, the temperature at which the first trace of liquid appears as the solution is heated.

melting point

the temperature at which a solid turns into a liquid. It is equal to the freezing point
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