The fusion is the change of state from solid to liquid for a substance over a temperature range. If the substance has a high degree of purity, the range corresponds to a specific temperature: the melting point. And when there is a certain degree of impurities, the melting point is represented by a range (for example, 120-122ºC).
It is one of the most common physical processes in nature. Solids absorb heat and raise their temperature until the first drops of liquid begin to form. Then other drops follow the first ones, and as long as all the solid has not melted its temperature remains constant..
Why? Because all the heat is consumed to produce more liquid, instead of heating the latter. Therefore, the solid and the liquid have the same temperature and coexist in equilibrium. If the heat supply is constant, the equilibrium ends up shifting to the complete formation of liquid.
For this reason, when an ice stalactite begins to melt in spring, once the change of state has begun, it will not end until it has been transformed into liquid water. In the image above it can be seen that even some ice crystals float inside a hanging drop.
Determining the melting point of an unknown substance is an excellent test to identify it (as long as it does not contain many impurities).
It also reveals how strong the interactions are between the molecules that make up the solid; as it melts at higher temperatures, the stronger its intermolecular forces will be.
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Fusion consists of a change of state from solid to liquid. The molecules or atoms in the liquid have a higher average energy as they move, vibrate and rotate at higher speeds. This creates as a consequence an increase in intermolecular space and, therefore, an increase in volume (although this is not the case with water).
As in the solid the molecules are in a more compact arrangement, they lack freedoms in their movement, and they have a lower average energy. For the solid-liquid transition to occur, the molecules or atoms of the solid must vibrate at higher speeds by absorbing heat..
As it vibrates, a set of molecules separates that come together to form the first drop. And so, fusion is nothing more than a melting of the solid caused by the effect of heat. The higher the temperature, the faster the solid will melt.
In particular, fusion can lead to the formation of tunnels and pores within the solid. This can be demonstrated through a dedicated experiment for children..
Melting refers to the heat melting of a substance or mixture. However, the term has also been used to refer to the melting of other substances that are not strictly classified as solids: emulsions.
The ideal example is ice cream. They are emulsions of frozen water (and in some, crystallized), with air and fats (milk, cream, cocoa, butter, etc.).
The ice cream melts or melts because the ice exceeds its melting point, the air begins to escape, and the liquid ends up dragging the rest of its components.
The chemistry of ice cream is extremely complex, and represents a point of interest and curiosity when considering the definition of fusion.
With respect to other solid mixtures, one cannot properly speak of a melting point for analytical purposes; that is, it is not a decisive criterion for identifying one or more substances. In a mixture, as one component melts, the others can dissolve in the liquid phase, which is diagonally opposite to a fusion..
For example, a solid ice-sugar-salt mixture will melt completely as soon as the ice begins to melt. Since sugar and salt are very soluble in water, it will dissolve them, but it does not mean that the sugar and salt have melted..
Some common examples of fusion can be found within the kitchen. Butters, chocolates, gum and other sweets melt if they receive direct sun heat, or if they are enclosed in hot spaces. Some sweets, such as marshmallows, are intentionally melted for the best enjoyment of their flavors.
Many recipes state that one or more ingredients must first be melted before being added. Cheeses, fats and honey (very viscous) are also among these ingredients.
To decorate certain spaces and objects, metals, glass and ceramics with different designs are used. These ornamentations can be seen on the terrace of a building, in the crystals and mosaics of some walls, or in the items for sale inside the jewelers.
They are all made up of materials that melt at very high temperatures, so they must first be melted or softened in order to be able to work on them and give them the desired shapes.
It is here then that incandescent iron is worked, as blacksmiths do in the manufacture of weapons, tools and other objects. Likewise, fusion allows obtaining alloys by welding two or more metals in different mass proportions..
From molten glass you can create decorative figures such as horses, swans, men and women, travel souvenirs, etc..
The main examples of melting in nature can be seen in the melting of icebergs; in lava, a mixture of rocks melted by the intense heat inside volcanoes; and in the crust of the planet, where the presence of liquid metals predominates, especially iron.
Listed below are a number of common substances with their respective melting points:
-Ice, 0ºC
-Paraffin, 65.6ºC
-Chocolates, 15.6-36.1ºC (note that it is a temperature range, because there are chocolates that melt at lower or higher temperatures)
-Palmitic acid, 63ºC
-Agar, 85ºC
-Phosphorus, 44ºC
-Aluminum, 658ºC
-Calcium, 851ºC
-Gold, 1083ºC
-Copper, 1083ºC
-Iron, 1530ºC
-Mercury, -39ºC (it is liquid at room temperature)
-Methane gas, -182ºC
-Ethanol, -117ºC
-Graphite carbon, 4073ºC
-Diamond coal, 4096ºC
As can be seen, generally metals, due to their metallic bonds, have the highest melting points. However, carbon exceeds them despite having covalent bonds, but with very stable molecular arrangements.
Small, apolar molecules, such as methane gas and ethanol, do not interact strongly enough to remain solid at room temperature.
From the rest, the strength of intermolecular interactions within the solid can be inferred by measuring its melting point. A solid that withstands scorching temperatures must have a very stable structure.
In general, nonpolar covalent solids have lower melting points than polar, ionic and metallic covalent solids.
This is perhaps one of the most artistic and simple experiments to explain fusion to children. You need:
-Some plates, in such a way that when the water freezes in them they form domes
-A large tray to ensure a surface where ice can melt without causing havoc
-Salt (may be the cheapest on the market)
-Vegetable dyes, and a dropper or spoon to add them
Once the ice domes have been obtained, and placed on the tray, a relatively small amount of salt is added to their surface. The mere contact of the salt with the ice will cause rivers of water that will wet the tray.
This is because ice has a high affinity for salt, and a solution occurs whose melting point is lower than that of ice..
A few drops of food coloring are then added to the domes. The color will penetrate the tunnels of the dome and all its pores, as the first consequences of its melting. The result is a carnival of colors trapped inside the ice.
Finally, the colorants will be mixed in the water in the tray, giving another visual spectacle to the little spectators..
Within a temperature controlled cabinet, a number of substances can be placed in heat resistant containers. The purpose of this experiment is to show teenagers that each substance has its own melting point..
What substances can be chosen? Logically, neither metals nor salts can enter the cabinet, as they melt at temperatures above 500ºC (the cabinet would melt).
Therefore, from the list of substances, those that do not exceed 100ºC could be chosen, for example: mercury (assuming that the cabinet can be cooled below -40ºC), ice, chocolate, paraffin and palmitic acid.
Teenagers (and children too) would watch mercury turn into a metallic black liquid; and then the melting of the white ice, the chocolate bars, the palmitic acid and finally the paraffin candle.
To explain why paraffin melts at higher temperatures than chocolate, it will be necessary to analyze its structures.
If both paraffin and palmitic acid are organic compounds, the former must consist of a heavier molecule, or a more polar molecule (or both at the same time). Giving an explanation of such observations could be left as homework for the students..
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