Freezing Point

What is Freezing Point?

Freezing point is a temperature at which a liquid turns into a solid. As with the melting point, an increase in the pressure tends to raise the freezing point too. In the case of mixtures and specific organic compounds like fats, the freezing point is lower than the melting point. When the mixture begins freezing, the solid that forms initially has a different composition than that of the liquid. The formation of solid changes the composition of remaining liquid, typically in a manner that slowly lowers the freezing point. The same principle gets used in successive melting, purifying mixtures, and freezing. You probably already know what is freezing point, but this article packs on lots of information about freezing, factors affecting it, supercooled liquid, and so on. 

Basics of Freezing Point

Freezing is nothing but the change of a substance from the state of liquid to solid. It means that a substance gets transformed from one state of matter to another state of matter. At freezing point, the solid and liquid state exists at the same time in equilibrium. The freezing point of a substance relies on atmospheric pressure. 

Freezing Point Defection – The freezing point is the temperature at which a liquid changes into solid, at normal atmospheric pressure. A more precise definition of a freezing point is the temperature at which liquid and solid phases coexist in the equilibrium. 

How Does Freezing Occur?

  • When a liquid freezes, it passes from a liquid state to the solid-state. When a substance is in a liquid state, its molecules are loosely bound. Also, the intermolecular forces of attraction between molecules are less than that of solids. 

  • In a liquid, water molecules are always in motion. They are continually bumping and jostling into each other, and they never stay in a single place for long. When the liquid cools, it loses thermal energy. As a result, water molecules slow down, and they come close together. 

  • When water begins to freeze, the molecules settle in a place; attractive forces hold them together and crystals of a solid start forming. Soon enough, you start noticing the regular formations like crystals. 

  • During the freezing process, the temperature of a substance stays the same. And at the same time, the particles in a liquid turn into crystalline solid. Since particles in a liquid have more energy than the particles in a solid, the energy gets released during freezing.    

Fun Fact - The freezing point of a liquid state of any substance is the same as the melting point of its solid-state. For instance, the freezing point of water is 0o Celsius, and the melting point of solid water is 0o Celsius too.    

Factors That Affect the Freezing Point 

  • Types of molecules: The types of molecules that constitute a liquid affect its freezing point. When the intermolecular forces between these molecules are strong, then the freezing point becomes high. 

  • On the other hand, if the intermolecular forces of attraction between molecules of the liquid are weak, then the freezing point becomes low. You can say that intermolecular forces of a liquid are directly proportional to its freezing point.

  • Also, there are two types of changes, physical and chemical, which can affect the freezing point. You can decrease the freezing point of a liquid by mixing another soluble substance in it. In a physical approach, you can obtain a lower freezing point by altering the pressure. 

  • Most importantly, changes in the pressure can increase or decrease the freezing point of a substance. Typically, pressure lower than 1atm reduces the temperature at which the substance freezes. But in the case of water, the higher the pressure, lower is the freezing point. 

Supercooled Liquid 

  • Supercooling is the process of chilling the liquid beyond its freezing point, without turning it into solid. In theory, the freezing point and melting point of a substance has to be the same. It applies to the majority of substances.

  • However, few substances have a light difference between their freezing and melting point. Such substances can get cooled beyond their freezing point while retaining their liquid state. These substances are nothing but supercooled liquids.  

  • In simple words, supercooling is a state where liquid doesn’t solidify upon exposing to a temperature below its freezing point. A perfect example of supercooling is something you see every day. The clouds at high altitudes are nothing but an accumulation of supercooled water droplets, below their freezing point.  

FAQ (Frequently Asked Questions)

1. Explain the Interconversion of States of Matter

There are primarily three states of matter – solid, liquid, and gas. These states of matter are interconvertible by application of temperature and pressure. When a solid substance gets heated, the intermolecular force of attraction among particles reduces and they get converted into liquids. Upon further heating the liquids, they turn into gas. These gases are invisible; they don’t have shape or volume as the intermolecular force of attraction between them is zero. And when a solid substance turns directly into gas, then it gets called as sublimation.    

2. What Happens During Freezing?

Freezing point refers to a temperature at which the substance freezes. It’s a physical property of any matter. The freezing process is where water or other liquid changes to a solid-state. Freezing takes place when the liquid gets cooled to a point, and particles don’t have enough energy to overcome the force of attraction among them. So, the particles stay in a fixed position while crowding together closely. The freezing point for water is 0° Celsius, and below that temperature, water exists in the form of ice.