Latent heat of fusion

The latent heat of fusion, denoted by

${𝐿}_{𝑓}$, is the amount of heat energy required to change a unit mass of a substance from a solid phase to a liquid phase (or vice versa) at constant temperature and pressure. It represents the energy needed to overcome the intermolecular forces holding the solid together and to convert it into a liquid without changing its temperature.

The latent heat of fusion is typically expressed in units such as joules per gram (J/g) or kilojoules per kilogram (kJ/kg). It varies for different substances and depends on factors such as the substance's molecular structure, intermolecular forces, and pressure.

Mathematically, the latent heat of fusion can be calculated using the formula:

${𝐿}_{𝑓}=\frac{𝑄}{𝑚}$

where:

• ${𝐿}_{𝑓}$ is the latent heat of fusion,
• $𝑄$ is the amount of heat energy absorbed or released during the phase change,
• $𝑚$ is the mass of the substance undergoing the phase change.

For example, the latent heat of fusion of water at its normal freezing point (0°C or 273.15 K) is approximately 334 J/g or 334 kJ/kg. This means that it takes 334 joules of energy to melt one gram of ice at 0°C into water, or 334 kJ to melt one kilogram of ice at 0°C into water, without changing the temperature.

Understanding the latent heat of fusion is essential in various applications, including heating and cooling systems, refrigeration, phase change materials, and thermal energy storage.