Fusion

Fusion, also known as melting, is a physical process that causes a substance to go from its solid state to its liquid state, also known as phase transition. Typically, this occurs when the internal energy of a solid increases, which is accomplished through the application of heat or pressure, which raises the temperature of the substance to the melting point. It is only at this temperature that the ordered state of ions or molecules in a solid decomposes into a less ordered state, and the solid “melts” and turns into a liquid.

Fusion is defined as the transformation of a solid into a liquid.

It is the transition of a substance from a solid state to a liquid state that is known as fusion. This is a phase change phenomenon, which means that a substance is transformed from one state of matter to another during the course of this process.

What is the process by which fusion occurs?

The majority of solids are tightly packed in a crystal lattice, with strong intermolecular forces of attraction between the molecules. Heat causes the internal binding energy of the crystal lattice to be overcome by the heat energy, resulting in weakening of the intermolecular forces of attraction as the heat passes through it. When the force between molecules weakens, it causes instability in the crystal lattice, causing molecules to separate from one another and begin moving in random directions. The melting of a substance is caused by the instability of the crystal lattice structure. According to the widely accepted theory of melting, when the temperature of a substance is raised by increasing the supply of heat or increasing the pressure applied to it, the molecules of the substance begin to vibrate at their respective locations in response. When the amplitude (or distance covered) of a vibration is greater than the interatomic distance of a substance, it causes vibrational instability, which ultimately results in the melting of the substance in question.

Melting Point

The temperature at which a solid changes its state from solid to liquid under atmospheric pressure is known as the melting point of the solid. This equilibrium between solid and liquid phases is maintained at the melting point, which means that at this point, both the solid and liquid states are present at the same time. The melting point of a substance is determined by the pressure of the surrounding atmosphere. 

Latent heat of fusion

After a substance has been heated to the point of melting, any additional heat applied after this point does not raise the temperature of the substance; rather, it is used entirely to change the phase of the substance from solid to liquid. The latent heat of fusion is the heat that is supplied to a solid at its melting point when it is at its melting point. It is defined as the amount of heat energy required to completely transform 1 kg of a solid into a liquid under normal atmospheric pressure. The term latent, which means hidden in Latin, is used to describe this heat because it is figuratively hidden because it does not appear on the temperature scale.

Solids can be heated to the point where the molecules that hold their bonds together break apart and form a liquid, if the temperature is raised sufficiently. The most common example is the transformation of solid ice into liquid water. This process, which is also known as melting or heat of fusion, results in the molecules within the substance becoming less organised as a result of the heat generated. When a substance transitions from a solid to a liquid state, the change in enthalpy (heat) is observed . A substance’s change in enthalpy (H) is negative when it transforms from one state to another, such as when it transforms from one liquid state to another. The freezing process, as it is commonly known, results in the molecules within the substance becoming more ordered as a result of the process.

First order phase transition

In terms of thermodynamics, the change in Gibbs free energy G of the substances is zero at the melting point, but there are non-zero changes in the enthalpy (H) and the entropy (S), which are known as the enthalpy of fusion (or latent heat of fusion) and the entropy of fusion, respectively. As a result, melting is classified as a first-order phase transition in the phase diagram. Melting occurs when the Gibbs free energy of the liquid is lower than the Gibbs free energy of the solid for a given material. The temperature at which this occurs is determined by the pressure in the surrounding environment.

Conclusion

In Physics, Fusion is defined as the transition of a substance from its solid state to its liquid state. This is a phase transition phenomenon, as the name implies. Essentially, it means that a substance is transformed from one state of matter (solid) to another (liquid) during this procedure (liquid). Fusion, whether by melting or any other means, is a physical condition characterised by the transformation of a substance from a solid to a liquid state. An object reaches the melting point when the internal energy of the solid increases, which is most commonly accomplished through the application of heat or pressure, raising the temperature of the object to the melting point.