# What is the Difference Between Latent Heat of Fusion and Solidification

The key difference between latent heat of fusion and solidification is that latent heat of fusion is the amount of heat required to convert a solid phase into a liquid phase of the same substance, whereas latent heat of solidification is the amount of heat required to convert the phase of a substance from liquid phase to solid phase.

Latent heat of fusion and solidification are two enthalpy values that come under the subtopic “latent heat” in thermodynamics. The latent heat is also known as latent energy or heat of transformation. This term refers to the amount of heat either released or absorbed by a thermodynamic system during a process that occurs at a constant temperature. Usually, these reaction processes are first-order phase transitions.

Latent heat gives the energy hidden in a substance that can be extracted from that substance when it changes its phase of matter at a constant temperature. Some examples that fall under the field of latent heat include the latent heat of fusion, latent heat of vaporization, latent heat of solidification, and latent heat of crystallization.

### CONTENTS

1. Overview and Key Difference
2. What is Latent Heat of Fusion
3. What is Latent Heat of Solidification
4. Latent Heat of Fusion vs Solidification in Tabular Form
5. Summary – Latent Heat of Fusion vs Solidification

## What is Latent Heat of Fusion?

Latent heat of fusion is the amount of heat a solid needs to change its phase from solid phase to liquid phase at a constant temperature, denoted by Hf. In other words, a unit mass of a substance requires heat energy that is equal to the latent heat of fusion (of that particular substance) at its melting point in order to convert into its liquid phase. Fusion is melting or liquefying a solid by providing heat. Different substances have different melting points; thus, different values for Hf.

Equation of Latent Heat of Fusion

The equation for Hf is as follows:

Hf  =ΔQf/ m

Here, ΔQf is the change in the energy of the substance, and m is the mass of the substance.

## What is Latent Heat of Solidification?

Latent heat of solidification is the amount of heat a solid substance needs to change its phase from liquid phase to solid phase at a constant temperature. We can denote this latent heat by Hs. Typically, the molecules in a liquid phase of a particular substance have high internal energy compared to the solid phase of the same substance. Therefore, upon the solidification process, energy is released from the reaction mixture.

Figure 01: Latent Heat Values for Water

## What is the Difference Between Latent Heat of Fusion and Solidification?

The key difference between latent heat of fusion and solidification is that latent heat of fusion is the amount of heat required to convert a solid phase into a liquid phase of the same substance, whereas latent heat of solidification is the amount of heat required to convert the phase of a substance from liquid phase to solid phase. Therefore, latent heat of fusion involves the conversion of the solid phase to its liquid phase, whereas latent heat of solidification involves the conversion of the liquid phase to its solid phase.

Below is a summary of the difference between latent heat of fusion and solidification in tabular form for side by side comparison.

## Summary – Latent Heat of Fusion vs Solidification

Latent heat of fusion and latent heat of solidification are opposite of each other in terms of phase change. The key difference between latent heat of fusion and solidification is that latent heat of fusion is the amount of heat required to convert a solid phase into a liquid phase of the same substance, whereas latent heat of solidification is the amount of heat required to convert the phase of a substance from liquid phase to solid phase.