The freezing point is the temperature at which the crystalline material solidifies, and is the temperature at which the vapor pressure of the liquid is equal to the vapor pressure of the solid. Different crystals have different condensation points. At a certain pressure, the freezing point of any crystal is the same as its melting point. In the same crystal, the freezing point is related to the pressure. When the volume expands during solidification, the freezing point decreases with the increase of pressure; when the volume shrinks during solidification, the freezing point increases with the increase of pressure. During solidification, the liquid turns into a solid while releasing heat. Therefore, when the temperature of the substance is higher than the melting point, it will be in a liquid state; below the melting point, it will be in a solid state. The amorphous material has no freezing point. Crystal solidification characteristics: Solidification begins when a certain temperature is reached; The temperature remains unchanged during solidification; Solid and liquid coexist when solidified; The solidification must be exothermic. Non-crystalline solidification characteristics: The temperature continues to decrease during solidification; Exothermic when solidified. Solidified image The solidified image clearly illustrates the solidification state of the crystal and the amorphous, as well as the solidification properties of each period. Freezing point of matter Note: Under normal atmospheric pressure, the unit (°C) Diamond: 3550 Tungsten: 3410 Pure iron: 1535 Various steels: 1300~1400 Various cast iron: around 1200 Copper: 1083 Gold: 1064 Silver: 962 Aluminum: 660 Lead: 327 Tin: 232 Sodium thiosulfate (Haibo): 48 Magnesium: 648.8 Mercury (mercury): -39 Alcohol: -117 Nitrogen: -210 Oxygen: -218 Hydrogen: -259 From the above table, it can be concluded that the freezing point refers to a temperature at which the liquid gradually becomes solid. The freezing point of various liquids is different. Example: What is the high freezing point mean high temperature or low temperature? Analysis: The high freezing point is a relative concept. The freezing point of one object is higher than the freezing point of another object, which means that when the object solidifies, the temperature requirement is lower when it solidifies than the other object, that is, in one It can be solidified at a higher temperature. Therefore, the high freezing point is relatively high in temperature. There are three special points in the change of state: freezing point, boiling point, melting point. Factor of change in freezing point (melting point) pressure The melting point of the substance (the freezing point, the same below) is usually referred to as the case of one atmosphere; if the pressure changes, the melting point also changes. There are two different conditions for the melting point to vary with pressure. For most substances, the melting process is a process in which the volume becomes larger. When the pressure increases, the melting point of these substances increases. For substances like water, unlike most substances, the process of melting ice into water is reduced. (The same is true for metal bismuth, antimony, etc.). When the pressure is increased, the melting point of ice is lowered. Dissolved with impurities If a small amount of other substances, or impurities, are dissolved in the liquid, even if the amount is small, the melting point of the substance (the freezing point, the same below) may vary greatly. For example, if the salt is dissolved in water, the melting point (the temperature at which the two phases of the solid and liquid coexist and balance) will be significantly reduced. The seawater is the salt-dissolved water, and the freezing temperature of the seawater in winter is lower than that of the river water. This is the reason. The melting point of the saturated brine can be lowered to about -22 °C. Example: In order to separate the mixture of alcohol and water, Zhang Xiao, based on the knowledge he has learned, proposes a solution: the water and alcohol can be separated according to the freezing point of water and alcohol. For this reason, he uses the freezer of the refrigerator in the home. I did the following experiment: He put a mixture of water and alcohol in different proportions into the freezer, and monitored the temperature of the mixture with a thermometer. Nail Files,Sponge Nail File,Multi-Function Nail File,Manicure Nail File Yangjiang Etina Houseware Co., Ltd. , https://www.jmstjsrobot.com