We express that what are the examples of freezing? with definition, freezing point, stages of freezing, and its uses. Lets Read….examples of freezing point
Definition of Freezing
Freezing is the physical change in which matter goes from a liquid to a solid state, due to a drop in temperature. Generally, the term freezing is used for substances that are liquid at standard conditions of temperature and pressure (1 atm, 25 ° C), also called environmental conditions.
Molecules in a liquid clump together more with each degree that the temperature decreases. In water (H 2 O), ordered structures called crystals are reached, which can be seen with the naked eye. The common name for water crystals is “ice”, and this can melt or become liquid again, if subjected to heating.
Freezing Point examples of freezing point
The freezing point is the temperature at which a liquid begins to transform into a solid and vice versa . It is the same as the melting point , because in it the solid becomes liquid. That of water has served as a reference to form the Celsius (or centigrade) scale of temperatures.
It was placed at 0 ° C and from there the other temperatures are marked. From this scale, the absolute centigrade or Kelvin has been established, in which the freezing point of water is at 273.15 K. Absolute zero, which is the lowest possible temperature, is at 0 K.
Each liquid has its own freezing point, and it will depend on the following properties:
- Your intermolecular forces
- The pressure to which you are subjected
When the intermolecular forces of a liquid are great , its particles are attracting each other and staying together . It will be easy for them to become a solid structure. Its freezing point will be a regular temperature .
On the other hand, if the intermolecular forces of a liquid are small , its particles will be freer and more dispersed . It will be difficult for them to become a solid structure. Its freezing point will have to be a very low temperature , close to 0 ° C or lower.
If a liquid is under great pressure , its particles will be more packed together, so it will only take a short cooling to freeze it. If the liquid is under little pressure or even a vacuum , its particles will be free, almost fluttering. It will take a lot of chilling to freeze it.
At atmospheric pressure, water freezes into crystals with a hexagonal structure. The size and structure of ice crystals depend on the rate of cooling.
Stages of Freezing
The formation of ice during the crystallization of water can be detailed in three stages:
- Maturation or Recrystallization
The nucleation , or initial step of forming seed crystals, is the process in which ice nuclei appear as a result of a first cooling. There are three types of nucleations:
- Homogeneous nucleation: water or a solution free of impurities is cooled. Pure nuclei are formed.
- Heterogeneous nucleation: water molecules gather around a nucleating agent, such as an insoluble material, for example.
- Secondary nucleation: if a crystal erodes, new nuclei are formed from it.
The propagation or crystalline growth is when the molecules diffuse until the surface of the crystalline nuclei that are growing. The presence of few amounts of impurities decreases the rate of spread.
The recrystallization is the change in the number, size, shape, orientation, or perfection of crystals after completion of the initial solidification. During recrystallization, as time passes, the average size of the ice crystals increases and their number decreases due to the redistribution of water from small ice crystals to large ones.
Uses of Freezing examples of freezing point
Freezing is a very useful physical change especially in the area of the food industry . All foods have in their composition a percentage of humidity (water H 2 O), which at room temperature can be a favorable environment for the decomposition or proliferation of microorganisms to develop .
To avoid food spoilage, freezing is used. This will keep it out of the room temperature range and also the water crystals will not allow the reproduction of life forms.
Examples of Freezing
Listed below are a series of temperatures at which various substances freeze:
- Helium (He): –272 ° C
- Hydrogen (H): –259 ° C
- Oxygen (O 2 ): –218 ° C
- Nitrogen (N 2 ): –210 ° C
- Carbon dioxide (CO 2 ): –78 ° C
- Ethyl alcohol (C 2 H 5 OH): –117 ° C
- Water (H 2 O): 0 ° C
- Tin (Sn): 232 ° C
- Lead (Pb): 327 ° C
- Aluminum (Al): 660 ° C
- Acetic acid (CH 3 COOH): 16.6 ° C
- Nitrobenzene (C 6 H 5 NO 2 ): 5.7 ° C
- Phenol (C 6 H 5 OH): 43 ° C
- Benzene (C 6 H 6 ): 5.48 ° C
- Ammonia (NH 3 ): –75 ° C
- Acetone (CH 3 OCH 3 ): –94.3 ° C
- Ethane (C 2 H 6 ): –183 ° C
- Propane (C 3 H 8 ): –188 ° C
- Para-dichlorobenzene (C 6 H 4 Cl 2 ): 53 ° C
- Maleic anhydride (C 4 H 2 O 3 ): 54 ° C