What is latent heat of fusion?

Short Answer

Latent heat of fusion is the amount of heat energy required to change a solid into a liquid at its melting point without changing its temperature. During this process, the solid absorbs heat, but its temperature stays constant until the entire solid becomes liquid. This heat is used to break the strong forces holding the particles in fixed positions.

A common example is ice melting into water. Ice absorbs latent heat of fusion at 0°C, but its temperature does not rise until all of it turns into water.

Detailed Explanation :

Latent Heat of Fusion

Latent heat of fusion is a special kind of heat energy needed to convert a solid into a liquid at its melting point without any rise in temperature. The word “fusion” means “melting.” When a solid is heated, its particles vibrate faster, but at the melting point, the heat energy supplied does not increase the temperature. Instead, it is used to overcome the intermolecular forces holding the particles together in the solid state. This extra heat that allows the change of state is called the latent heat of fusion.

This concept is very important for understanding how solids melt and how temperature behaves during melting. It also helps explain why ice remains at 0°C until completely melted and why melting involves energy even though temperature does not increase.

How Latent Heat of Fusion Works

  1. Heating the Solid

When a solid is heated, its particles gain energy and vibrate faster. The temperature of the solid increases until it reaches its melting point.

  1. Reaching the Melting Point

At the melting point, the solid begins to melt. At this stage:

  • The temperature becomes constant.
  • Both solid and liquid exist together.
  • Heat continues to be absorbed.

Even though heat is being supplied, the thermometer reading does not change.

  1. Breaking Intermolecular Forces

The heat energy supplied at the melting point is used to:

  • Break the strong forces holding particles in fixed positions
  • Allow particles to move freely as they become liquid

This energy is not used to raise temperature, which is why melting occurs at constant temperature.

  1. Complete Melting

Once all the solid has melted:

  • The particles are free to move
  • The substance becomes a liquid
  • Temperature begins to rise again if heating continues

Until the entire solid melts, no temperature change occurs.

Why Latent Heat of Fusion Is Important

Latent heat of fusion plays a crucial role in the following areas:

  1. Natural Processes
  • Ice melting in nature
  • Glacier movement
  • Snow turning into water during warmer seasons

These processes help maintain the Earth’s temperature balance.

  1. Weather and Climate

Melting of ice absorbs a lot of heat, helping in moderate climate conditions.

  1. Daily Life Activities
  • Melting ice to cool drinks
  • Defrosting refrigerators
  • Melting butter or chocolate while cooking

These processes rely on the energy required for fusion.

  1. Science and Industry
  • Manufacturing of metals
  • Casting and molding
  • Cooling systems
  • Food freezing and thawing

Latent heat of fusion is used to control temperatures in many industrial processes.

Examples of Substances and Their Latent Heat of Fusion

Different substances require different amounts of heat to melt.

  • Ice has a latent heat of fusion of about 334 J/g.
  • Wax has a lower latent heat of fusion because its particles are held with weaker forces.
  • Metals like iron or lead need very high latent heat due to strong particle bonds.

These differences depend on the strength of intermolecular forces in the solid.

Relation Between Melting Point and Latent Heat of Fusion

  • A higher melting point does not always mean higher latent heat.
  • Latent heat depends on bond strength, not only temperature.
  • Pure substances have a fixed melting point and fixed latent heat.

Impure substances melt over a range of temperatures and may require more or less heat.

Latent Heat of Fusion in Water

Water has a very high latent heat of fusion compared to most substances. This is why:

  • Ice does not melt instantly even in warm conditions.
  • A large amount of heat is required to melt ice.
  • Water bodies regulate climate by absorbing heat during melting.

This property makes water important for life and environmental stability.

Energy Absorbed During Ice Melting

When ice melts:

  • It absorbs heat from the surroundings
  • Temperature stays at 0°C
  • Heat is used for breaking bonds
  • The surrounding air becomes cooler

This is why we feel cool when holding ice.

Conclusion

Latent heat of fusion is the heat energy needed to convert a solid into a liquid at its melting point without changing its temperature. It is used to break the strong intermolecular forces that hold particles in fixed positions. This important physical property helps explain the melting process, natural temperature regulation, and various industrial and daily-life applications. Understanding latent heat of fusion helps us better understand how matter behaves during state changes.