Why is energy absorbed during melting but released during freezing?

Energy is absorbed during melting to overcome intermolecular forces, while it's released during freezing as these forces are established.

Melting and freezing are phase transitions that involve changes in the state of matter. During melting, a solid turns into a liquid, and this process requires energy. The energy is used to overcome the intermolecular forces that hold the particles together in the solid state. These forces are quite strong, and breaking them requires a significant amount of energy. This energy is absorbed from the surroundings, which is why melting is an endothermic process.

On the other hand, freezing is the process where a liquid turns into a solid. During freezing, the particles of the substance come closer together and the intermolecular forces become stronger. As these forces are established, energy is released. This is because the formation of intermolecular bonds is an exothermic process, meaning it releases energy.

The amount of energy absorbed during melting or released during freezing is known as the latent heat of fusion. This is the amount of energy required to change one kilogram of a substance from solid to liquid (or vice versa) without changing its temperature. It's important to note that while these processes involve changes in energy, they do not involve changes in the temperature of the substance. This is because the energy is used or released in changing the state of the substance, not in increasing or decreasing its kinetic energy (which would change its temperature).

In summary, the absorption or release of energy during melting or freezing is due to the changes in intermolecular forces that occur during these phase transitions.