What is freezing?

Short Answer

Freezing is the process in which a liquid changes into a solid when its temperature decreases. When a liquid loses heat, its particles slow down and come closer until they are fixed in place, forming a solid.

Freezing happens at a specific temperature called the freezing point. For water, the freezing point is 0°C. Freezing is a physical change and can be reversed by heating the solid to melt it again.

Detailed Explanation :

Freezing

Freezing is an important physical process that explains how a liquid becomes a solid when heat is removed from it. Every liquid is made of tiny particles—molecules—that move freely and have enough energy to flow. When heat is taken away from the liquid, the movement of these molecules slows down. As the temperature continues to drop, the particles lose more energy and come very close to each other. Eventually, they become fixed in a definite arrangement, forming a solid. This change of state from liquid to solid is known as freezing.

Freezing is the opposite of melting. While melting happens when a solid absorbs heat, freezing happens when a liquid loses heat. Freezing is a reversible physical change, which means that the solid formed can be turned back into a liquid by heating.

Meaning of freezing

Freezing can be defined as:

“The process by which a liquid turns into a solid when its temperature is lowered to the freezing point.”

Freezing occurs at a specific temperature called the freezing point. This temperature is the same as the melting point of the substance.

Examples:

  • Water freezes at 0°C
  • Coconut oil freezes around 20–25°C
  • Mercury freezes at –39°C

What happens during freezing

Many microscopic changes occur during freezing:

  1. Loss of heat
    The liquid gives out heat energy to the surroundings.
  2. Particles slow down
    Due to the loss of energy, particles move more slowly.
  3. Attraction increases
    With slower movement, the attractive forces between particles become stronger.
  4. Particles take fixed positions
    The particles arrange themselves in a regular pattern, forming a solid.
  5. Temperature stays constant
    During freezing, the temperature remains the same until the entire liquid becomes solid.

This entire process creates a solid with a definite shape and volume.

Freezing point

The freezing point is the temperature at which a liquid starts becoming a solid. It depends on the nature of the substance.

Examples of freezing points:

  • Water: 0°C
  • Ghee: around 25°C
  • Iron: 1538°C
  • Oxygen: –218°C

A pure substance freezes at a fixed temperature, but impure substances freeze over a range.

Latent heat of fusion

Even after reaching the freezing point, a liquid must lose extra heat to change into a solid. This heat is called latent heat of fusion. It is the heat released during the freezing process. This is why ice does not form instantly at 0°C; water must release more heat before it becomes solid.

Examples of freezing in daily life

Freezing is a common process that we observe in everyday situations:

  1. Water turning into ice in the freezer
  2. Making ice cream
  3. Melting and refreezing of snow in winter
  4. Coconut oil solidifying in cold weather
  5. Hot liquids turning cold and becoming solid (like ghee or wax)

These examples show how freezing is a natural and useful process.

Factors affecting freezing

Several factors influence the freezing process:

  1. Temperature

Lower temperature speeds up freezing. Higher temperature slows it down.

  1. Impurities

Impurities lower the freezing point.
Example: Adding salt to ice causes it to melt at temperatures below 0°C.

  1. Pressure

Changes in pressure may increase or decrease the freezing temperature of some substances.

  1. Cooling rate

Quick cooling forms small crystals, while slow cooling forms large crystals.

Importance of freezing

Freezing is used in many fields:

  1. Food preservation

Freezing slows down bacterial growth, keeping food fresh.

  1. Weather and climate

Freezing of water affects snowfall, ice formation, and ocean currents.

  1. Construction

Freezing affects roads, soil, and building materials in cold regions.

  1. Science and industry

Freezing is used in making ice packs, preserving biological samples, and manufacturing chemicals.

Freezing as a physical change

Freezing does not change the chemical identity of the substance. Water becomes ice, but both are still H₂O. Similarly, melted wax or ghee turns solid again without any chemical change. This makes freezing a reversible and purely physical process.

Conclusion

Freezing is the process in which a liquid changes into a solid when its temperature decreases. The liquid loses heat, its particles slow down, and they settle into fixed positions to form a solid. This process happens at a fixed freezing point and involves the release of latent heat. Freezing is essential in nature, daily life, and various industries. It is a reversible physical change that helps us understand how matter behaves when cooled.