Matter is everything that surrounds us that has mass and weight, that occupies a place in the space, that is perceptible by one of our senses and that is opposed to changing position, which is, that has inertia. 

The environment that surrounds us is composed of matter. Thanks to our senses we are able to recognize or perceive various types of matter. Some of them are easily recognizable, such as a coin, which we can see, touch and therefore recognize quite easily, but there are others which we cannot perceive them with the same ease way, such as the air. 

   Matter consists of hundreds of elementary particles that are coupled together to form atoms that join together to form molecules, that are subject to two antagonistic forces, which are cohesion and repulsion. Due to these forces and the predominance of one over the other, the matter is present in three forms: liquid, solid and gaseous, known as “states of matter”. 

States of matter
Solid	Liquid	Gaseous
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It has a defined shape and volume, because the force of attraction is bigger than the repulsion one.	It has a defined volume but a variable form due to it depends on the vessel that contains it. There is a balance between its forces of attraction and repulsion.	It has neither form nor definite volume because its force of repulsion is much bigger than the attraction one.

In nature, we can observe changes of matter in a frequent way, like the well-known case of water, which can be found in solid, liquid and gaseous forms. Bodies can change from one state to another due to the effect that temperature and pressure produce on them, either increasing or decreasing said factors.

   In a general and more visual way, we can understand the different changes of state through the subject can pass: 

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1. Progressive changes of state: They occur when we increase the temperature of their bodies through the application of heat, such as: melting, evaporation and direct sublimation.  
   • Melting: It is the change from the solid state to the liquid state through the application of heat. The temperature at which this process occurs depends on each substance, being called at said temperature “Fusion Point”. In the case of gold, for example, it is 1064º C while in the case of ice it is 0º C.
     

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   • Evaporation: It is the change form the liquid state to the gaseous state. This process can occur at room temperature, only passing the particles from the surface to the gaseous state. If heat is applied both the particles of the surface and those of the interior can go into the gaseous state. The temperature necessary to reach this point is called the “Boiling Point” and is characteristic of each substance. For the case of silver it is 2162 ºC, while in the case of water it is only 100 ºC.
     

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     In a properly adapted laboratory there are different ways to perform this process. One of them is through the REFLUX, where with a heating plate, we increase the temperature of the substance in liquid state, until reaching its boiling point. At this temperature steam starts to rise up the column and we can then condense it again to pick it up if we are interested on it.  

     

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   • Direct Sublimation: It is the change from the solid state to the gaseous state by aun increase in the temperature. In nature there are some substances that can undergo such transformation as for example metal iodine, sulfur, dry ice or benzoic acid among others.   If we study the case of dry ice (CO2) in the laboratory, we can see that the transformation is immediate when we add a few drops of ethanol.
     

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     Industrially, this process can be carried out quickly and effectively, thanks to the “lyophilizer”.

     

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     With the LIOFILIZATION we can eliminate the water present in solutions due to the conditions of low pressure and low temperature that the equipment facilitates us. The present water is removed by freezing and subsequent sublimation of the ice. When the machine supplies heat, the ice passes from its solid phase to the gaseous one without reaching the boiling point of the water and therefore without passing through the liquid phase.

2. Regressive state changes: They are those which occur when the temperature of the bodies decreases, that is, they are colder, such as: solidification, condensation and regressive sublimation.  
   • Solidification: It is the passage of a substance from the liquid state to the solid state. For this process to occur, the substance must reach a certain temperature known as the “Freezing Point” and, because of this process is the reverse of the melting point, it coincides with the temperature of the Melting Point.    In our daily lives we see sometimes this process with the water, which forms ice when we lower its temperature. But in the laboratory we can perform many solidications, the best known is CRYSTALLIZATION.  
     

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     Crystallization is a technique widely used in the laboratory to purify substances that normally contain impurities. A substance that crystallizes easily is KH2PO4 (monopotassium phosphate) after making a saturated solution of said compound with hot water.  

      

     Crystallization of KH2PO4
     A saturated solution of approximately 3.5g of mono potassium phosphate in 20mL of hot water is made.	Bioprofe | Changes of states of matter | 11
     After the complete dissolution of the mixture and without waiting for it is cold, it is poured over the container.	Bioprofe | Changes of states of matter | 12
     The saturated solution begins to ascend through absorption by the paper and as it cools, crystallization takes place acquiring the green hue due to the color previously used in the paper.	Bioprofe | Changes of states of matter | 13
     The crystallization ends when all the monopotassium phosphate solution has been consumed.	Bioprofe | Changes of states of matter | 14

   • Condensation: It is the change of gaseous state to liquid state due to a decrease in the temperature. The temperature at which this transformation occurs is known as the “Condensation Point” and corresponds to the Boiling Point because of this process is inverse to that of evaporation.   In the laboratory, this change is normally obtained thanks to the realization of an assembly with a fractionating column, which are glass tubes filled with a package and placed between the matrix and the distillation head.  
     

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     The steam condenses in the filling of the column, evaporating again and condensing once more in the upper plate. Next, a coolant is fitted in which, thanks to the constant passage of cold water around it, we can condense the gas so that it can be collected at its outlet.  

   • Regresive Sublimation: t is the change from the gaseous state to solid state but without passing through the liquid state.    CAs we have already mentioned, there are several products that can be sublimated when they are heated   It is the example of benzoic acid, which if previously covered, we heat it with caution, vapors are produced inside with the color of the acid.  
     

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     If we put in contact the steam obtained in the sublimation with a cold surface, like a lid, the benzoic acid undergoes an inverse sublimation forming crystals of high purity. 

     

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     There are two more states in which matter can be found, but they are not well known. The characteristics they need to be present are very concrete and it is not possible, for now, the transformation of matter between these states and others. Therefore, they can not be included with the previous states.

3. Plasmatic state: It is a state that is characterized by being very energetic and able to be generated only in situations of very high temperature. In this state all atoms are ionized and with some free electrons present.    It is the most common state in the universe, it allows electricity to be conducted but it has no fixed shape or volume. In this state are for example the rays, the stars or even the Sun.   In our lives it is also very present because this state has favored the formation of fluorescent bulbs of low electrical consumption or flat screen televisions composed of the noble gases xenon and neon.  
4. Condensed state of Bose-Einstein: It owes its name to Satyendra Nath Bose and Albert Einstein, who predicted its existence. This state only occurs in some gaseous superfluids that are cooled to temperatures very close to absolute zero (-273ºC).   The main characteristic of this state is that a macroscopic quantity of the particles of the material that compose it pass to the minimum energy level, called the fundamental state.  

You can download the App BioProfe READER to practice this theory with self-corrected exercises.