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fusion A process that changes the state of matter from a solid to a liquid. The internal energy of the solid phase increases (usually due to the application of heat) to a certain temperature (called the melting point) at which it turns into the liquid phase, and a completely melted body is called moltenMelting occurs at the temperature at which the solid and liquid phases of a pure substance are in equilibrium. Upon reaching the melting point, more heat will lead to the gradual transformation of the solid body into a liquid without a change in temperature, but during this state it gets what is called the heat of fusion. Melting point Andfusion heat Two properties of matter. The heat of fusion of a substance is when all of the solid has melted, the additional heat will raise the temperature of the liquid.

Example: Snow melts at a temperature of 0 degrees Celsius, and its heat of fusion is 333,500 J/kg. That heat is needed to turn 1 kilogram of ice into water. During the transformation process, the temperature remains constant at zero degrees Celsius until all the ice has been converted to water.

The melting point of a crystalline solid is a characteristic of a substance, used to identify compounds and pure elements. Most mixtures and non-crystalline bodies (morphic = the distribution of atoms is random without organization) melt within a range of temperatures.

The melting point of a solid is generally the same freezing point liquid substance. The liquid may freeze according to several different crystal systems, and because impurities lower the freezing temperature, the reality requires that the freezing temperature is not equal to the melting temperature. Thus, to determine the identity of the substance, the melting temperature is used. For example, water crystals need nuclei around which crystals begin to form. Water in a clean glass will cool to several degrees below its freezing point without freezing.

From a thermodynamic point of view, the change in the Gibbs free energy of a substance at the melting point is equal to zero, due to the increase in heating (H) and entrapment (S) a (ΔH,ΔS > 0). Melting occurs when the Gibbs free energy of the liquid state becomes less than that of the solid state. And at various pressures, this happens at a specific temperature. It can also be:

$\displaystyle \Delta S=\frac \Delta HT$

Where “

$\displaystyle T$

“،”

$\displaystyle \Delta S$

“, And”

$\displaystyle \Delta H$

are respectively the temperature at the melting point, the change in the entropy of fusion, and the change in the heating element of fusion.

melting of a solid[عدل]

When we heat a pure solid, its temperature begins to rise until it reaches its melting point and converts the heat absorbed by the solid into a liquid. During that period the temperature of the system remains constant until all solid matter changes to a liquid state (phase transition). After each piece of solid material turns into a liquid, the temperature of the liquid begins to increase with the continuation of heating. The temperature of the liquid continues to rise until its temperature reaches the boiling point, at which point the liquid begins to turn into vapor. This is also another phase shift.

During the evaporation process, the system temperature remains constant. For example, with regard to water, the temperature of the boiling water remains constant at 100 degrees Celsius until all the water turns into steam. During this time, steam stores the heat it gained during its transition from a liquid state to a gaseous state in the form of latent heat.

The amount of heat required for the fusion of a substance is called the heat of fusion, enthalpy of fusion, or latent heat of fusion, and it is measured in joules/mol, or measured in joules/kg.

The graph shows the change of temperature (vertical axis) of the solid with the heating time (horizontal axis). We see the constancy of the temperature when the solid is transformed into a liquid, as well as the constancy of the temperature at the boiling point during the transformation of the liquid into vapor.

The heat of fusion of some substances[عدل]

Subject	Heat of fusion (kJ/kg)	heat of fusion (kJ/mol)
aluminium	398	10,7[1]
Lead	23,4	4,85[2]
chrome	325	16,93[3]
Iron	268	15,0
gold	63	12,4
graphite	16750	201
cadmium	55	6,2[4]
potassium	63	2,5
cobalt	291,8	17,2[5]
Carbon Dioxide	180	7,9
copper	210	13,3[6]
magnesium	373	9,1
manganese	264	14,5
Sodium	113	2,6[7]
Nickel	301	17,7
Paraffin	200 … 240
phosphorous	21	0,7
Platinum	100	19,5
Mercury	11,81	2,37[8]
oxygen	13	0,2
l sulfur (monoklin)	38	1,2
Silver	105	11,3
silicon	1803,7	50,66[9]
Candle	176
Water	333,5	6,01
hydrogen	59	0,06
tungsten	191,3	35,2[10]
zinc	113	7,4[11]
tin	59	7,03[12]

Incompatible fusion[عدل]

incompatible fusion Incongruent melting) is the dilution of a solid material associated with the dissolution or interaction of the solid material with the molten material to give another solid material and a liquid phase that differ in their composition from the original solid material. For example, enstatite (Enstatite), which is a magnesium silicate MgSiO₃fused incompatible at low pressure to form forsterite (Forsterite) which is another type of magnesium silicate Mg₂SiO₄a silica-rich SiO liquid₂. At pressures between 2.5 and 5.5 kbar, the fusion of enstatite becomes compatible.

Read also[عدل]

• boiling temperature
• heat of evaporation

the reviewer[عدل]

• Encyclopedia Britannica This site was accessed on October 7, 2008

Matter transformations (

• A
• N
• T

)

		to me
		solid	liquid	Gas	plasma
From	solid		fusion	sublimation
	liquid	Freeze		Evaporation
	Gas	deposition	intensified		ionize
	plasma			Plasma reconstitution

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